Prof. Dr. Ferdi Schüth

Heterogeneous Catalysis
Max-Planck-Institut für Kohlenforschung

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  • Catalytic reactions in ball mills
    Amrute, A.P. and Schüth, F.
    Catalysis 33 (2021)
    Over the past two decades mechanochemistry has emerged as an important tool in catalysis research. It has not only shown promise for catalyst synthesis, resulting in properties that are often unattainable by conventional methods, but is also a very effective tool for performing catalytic reactions with exceptional selectivities. Besides, in several instances, it allows reactions under much milder conditions compared to thermochemical methods. In this chapter, we attempt to give an overview of these efforts with a focus on catalytic reactions in ball mills. Through the selection of prominent examples from the literature, from early mentions in 300 B.C. to recent times, we try to analyze how mechanical forces lead to chemical reactions and what effect they cause to materials or chemical reactions. We also discuss the state-of-the-art milling devices, and then cover broadly chemical reactions in ball mills. The latter part briefly tackles materials synthesis, but mainly focuses on chemical reactions of solid-solid and gas-solid nature from both organic synthesis and heterogeneous catalysis. The chapter also touches on the aspects of in situ analysis and scale-up with relevant literature. The latter areas are currently in the focus of attention to develop deeper understanding and to eventually find ways to make mechanocatalysis industrially applicable. © The Royal Society of Chemistry 2021.
    view abstract10.1039/9781839163128-00307
  • Chemical Vapor Deposition of Hollow Graphitic Spheres for Improved Electrochemical Durability
    Knossalla, J. and Mielby, J. and Göhl, D. and Wang, F.R. and Jalalpoor, D. and Hopf, A. and Mayrhofer, K.J.J. and Ledendecker, M. and Schüth, F.
    ACS Applied Energy Materials 4 (2021)
    The wet-chemical synthesis of hollow graphitic spheres, a highly defined model catalyst support for electrocatalytic processes, is laborious and not scalable, which hampers potential applications. Here, we present insights into the chemical vapor deposition (CVD) of ferrocene as a simple, scalable method to synthesize hollow graphitic spheres (HGScvd). During the CVD process, iron and carbon are embedded in the pores of a mesoporous silica template. In a subsequent annealing step, iron facilitates the synthesis of highly ordered graphite structures. We found that the applied temperature treatment allows for controlling of the degree of graphitization and the textural properties of HGScvd. Further, we demonstrate that platinum loaded on HGScvd is significantly more stable during electrochemical degradation protocols than catalysts based on commercial high surface area carbons. The established CVD process allows the scalable synthesis of highly defined HGS and therefore removes one obstacle for a broader application. © 2021 The Authors. Published by American Chemical Society.
    view abstract10.1021/acsaem.1c00643
  • Flexibilization of Biorefineries: Tuning Lignin Hydrogenation by Hydrogen Partial Pressure
    Cao, Z. and Xu, Y. and Lyu, P. and Dierks, M. and Morales-García, Á. and Schrader, W. and Nachtigall, P. and Schüth, F.
    ChemSusChem 14 (2021)
    The present study describes an interesting and practical catalytic system that allows flexible conversion of lignin into aromatic or aliphatic hydrocarbons, depending on the hydrogen partial pressure. A combination of experiment and theory shows that the product distribution between aromatics and aliphatics can be simply tuned by controlling the availability of hydrogen on the catalyst surface. Noticeably, these pathways lead to almost complete oxygen removal from lignin biomass, yielding high-quality hydrocarbons. Thus, hydrogen–lignin co-refining by using this catalytic system provides high flexibility in hydrogen storage/consumption towards meeting different regional and temporal demands. © 2020 The Authors. ChemSusChem published by Wiley-VCH GmbH
    view abstract10.1002/cssc.202002248
  • Highly Ordered Mesoporous Co3O4 Electrocatalyst for Efficient, Selective, and Stable Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid
    Wang, C. and Bongard, H.-J. and Yu, M. and Schüth, F.
    ChemSusChem (2021)
    Electrochemical oxidation of biomass substrates to valuable bio-chemicals is highly attractive. However, the design of efficient, selective, stable, and inexpensive electrocatalysts remains challenging. Here it is reported how a 3D highly ordered mesoporous Co3O4/nickel foam (om-Co3O4/NF) electrode fulfils those criteria in the electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to value-added 2,5-furandicarboxylic acid (FDCA). Full conversion of HMF and an FDCA yield of >99.8 % are achieved with a faradaic efficiency close to 100 % at a potential of 1.457 V vs. reversible hydrogen electrode. Such activity and selectivity to FDCA are attributed to the fast electron transfer, high electrochemical surface area, and reduced charge transfer resistance. More impressively, remarkable catalyst stability under long-term testing is obtained with 17 catalytic cycles. This work highlights the rational design of metal oxides with ordered meso-structures for electrochemical biomass conversion. © 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH
    view abstract10.1002/cssc.202002762
  • Mechanochemical Synthesis of Catalytic Materials
    Amrute, A.P. and De Bellis, J. and Felderhoff, M. and Schüth, F.
    Chemistry - A European Journal (2021)
    The mechanochemical synthesis of nanomaterials for catalytic applications is a growing research field due to its simplicity, scalability, and eco-friendliness. Besides, it provides materials with distinct features, such as nanocrystallinity, high defect concentration, and close interaction of the components in a system, which are, in most cases, unattainable by conventional routes. Consequently, this research field has recently become highly popular, particularly for the preparation of catalytic materials for various applications, ranging from chemical production over energy conversion catalysis to environmental protection. In this Review, recent studies on mechanochemistry for the synthesis of catalytic materials are discussed. Emphasis is placed on the straightforwardness of the mechanochemical route—in contrast to more conventional synthesis—in fabricating the materials, which otherwise often require harsh conditions. Distinct material properties achieved by mechanochemistry are related to their improved catalytic performance. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstract10.1002/chem.202004583
  • Mechanochemical Synthesis of Supported Bimetallic Catalysts
    De Bellis, J. and Felderhoff, M. and Schüth, F.
    Chemistry of Materials 33 (2021)
    In a previous publication, ball milling was introduced as an effective method for the preparation of supported metal catalysts, simply from the coarse powders of the metal and metal oxide support. In this follow-up study, we demonstrate that mixing multiple metal sources can result in supported alloyed nanoparticles, extending the field of application of the method to the synthesis of supported bimetallic catalysts. Ball milling Au and Pd or Au and Cu in a high-energy regime (shaker mill) indeed led to the formation of Au-Pd and Au-Cu nanoparticles, supported on MgO or yttria-stabilized zirconia (YSZ), which were explored as model systems. Powder X-ray diffraction and electron microscopy were the primary means to investigate as-synthesized materials. The catalytic performance in CO oxidation was also investigated to understand better how the synthetic method could affect the features of the final materials as catalysts. © 2021 The Authors. Published by American Chemical Society.
    view abstract10.1021/acs.chemmater.0c04134
  • S-PEEK as a Catalyst for Gas Phase OME Synthesis
    Kley, K.S. and Grünert, A. and Schmidt, W. and Schüth, F.
    ChemCatChem 13 (2021)
    Oxymethylene ethers are a diesel additive/alternative, which reduce pollutant emissions. Based on methanol, it is possible to produce them from renewable energy and CO2. Sulfonated ion exchange resins are known to catalyze the synthesis of OME in liquid phase. Here, we report that the sulfonated polymer polyether-ether-ketone (S-PEEK) exhibits outstanding catalytic properties in the gas phase synthesis of OMEn. PEEK was reacted with gaseous SO3 to a degree of 22 % sulfonated monomer units. Using this material as a catalyst in the direct conversion of formaldehyde and methanol, an extraordinary selectivity to OME1 and OME2 of 93 % at equilibrium conversion of 55 % was obtained. Further, it was shown that the catalyst is stable for more than 60 h, and that with increasing reaction time selectivity to OME2 increases. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH
    view abstract10.1002/cctc.202100191
  • Synthetic ferripyrophyllite: Preparation, characterization and catalytic application
    Qiao, Y. and Theyssen, N. and Spliethoff, B. and Folke, J. and Weidenthaler, C. and Schmidt, W. and Prieto, G. and Ochoa-Hernández, C. and Bill, E. and Ye, S. and Ruland, H. and Schüth, F. and Leitner, W.
    Dalton Transactions 50 (2021)
    Sheet silicates, also known as phyllosilicates, contain parallel sheets of tetrahedral silicate built up by [Si2O5]2- entities connected through intermediate metal-oxygen octahedral layers. The well-known minerals talc and pyrophyllite are belonging to this group based on magnesium and aluminium, respectively. Surprisingly, the ferric analogue rarely occurs in nature and is found in mixtures and conglomerates with other materials only. While partial incorporation of iron into pyrophyllites has been achieved, no synthetic protocol for purely iron-based pyrophyllite has been published yet. Here we report about the first artificial synthesis of ferripyrophyllite under exceptional mild conditions. A similar ultrathin two-dimensional (2D) nanosheet morphology is obtained as in talc or pyrophyllite but with iron(iii) as a central metal. The high surface material exhibits a remarkably high thermostability. It shows some catalytic activity in ammonia synthesis and can serve as catalyst support material for noble metal nanoparticles. © The Royal Society of Chemistry.
    view abstract10.1039/d0dt03125a
  • The Impact of Antimony on the Performance of Antimony Doped Tin Oxide Supported Platinum for the Oxygen Reduction Reaction
    Jalalpoor, D. and Göhl, D. and Paciok, P. and Heggen, M. and Knossalla, J. and Radev, I. and Peinecke, V. and Weidenthaler, C. and Mayrhofer, K.J.J. and Ledendecker, M. and Schüth, F.
    Journal of the Electrochemical Society 168 (2021)
    Antimony doped tin oxide (ATO) supported platinum nanoparticles are considered a more stable replacement for conventional carbon supported platinum materials for the oxygen reduction reaction. However, the interplay of antimony, tin and platinum and its impact on the catalytic activity and durability has only received minor attention. This is partly due to difficulties in the preparation of morphology- and surface-area-controlled antimony-doped tin oxide materials. The presented study sheds light onto catalyst-support interaction on a fundamental level, specifically between platinum as a catalyst and ATO as a support material. By using a previously described hard-templating method, a series of morphology controlled ATO support materials for platinum nanoparticles with different antimony doping concentrations were prepared. Compositional and morphological changes before and during accelerated stress tests are monitored, and underlying principles of deactivation, dissolution and catalytic performance are elaborated. We demonstrate that mobilized antimony species and strong metal support interactions lead to Pt/Sb alloy formation as well as partially blocking of active sites. This has adverse consequences on the accessible platinum surface area, and affects negatively the catalytic performance of platinum. Operando time-resolved dissolution experiments uncover the potential boundary conditions at which antimony dissolution can be effectively suppressed and how platinum influences the dissolution behavior of the support. © 2021 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.
    view abstract10.1149/1945-7111/abd830
  • Carbon Supported Phosphoric Acid Catalysts for Gas-Phase Synthesis of Diesel Additives
    Grünert, A. and Schmidt, W. and Schüth, F.
    Catalysis Letters (2020)
    Abstract: Carbon supported phosphoric acid (H3PO4/C) was found to be a more productive catalyst for the gas-phase synthesis of the diesel fuel additive/substitute oxymethylene ethers (OME) as compared to benchmark zeolite catalysts. In this contribution, the performance of catalysts H3PO4/C and related H2PO4 −/C and HPO4 2−/C materials in OME synthesis from methanol and formaldehyde is described. Graphic Abstract: [Figure not available: see fulltext.]. © 2020, The Author(s).
    view abstract10.1007/s10562-020-03200-4
  • Direct Atomic-Level Imaging of Zeolites: Oxygen, Sodium in Na-LTA and Iron in Fe-MFI
    Mayoral, A. and Zhang, Q. and Zhou, Y. and Chen, P. and Ma, Y. and Monji, T. and Losch, P. and Schmidt, W. and Schüth, F. and Hirao, H. and Yu, J. and Terasaki, O.
    Angewandte Chemie - International Edition 59 (2020)
    Zeolites are becoming more versatile in their chemical functions through rational design of their frameworks. Therefore, direct imaging of all atoms at the atomic scale, basic units (Si, Al, and O), heteroatoms in the framework, and extra-framework cations, is needed. TEM provides local information at the atomic level, but the serious problem of electron-beam damage needs to be overcome. Herein, all framework atoms, including oxygen and most of the extra-framework Na cations, are successfully observed in one of the most electron-beam-sensitive and lowest framework density zeolites, Na-LTA. Zeolite performance, for instance in catalysis, is highly dependent on the location of incorporated heteroatoms. Fe single atomic sites in the MFI framework have been imaged for the first time. The approach presented here, combining image analysis, electron diffraction, and DFT calculations, can provide essential structural keys for tuning catalytically active sites at the atomic level. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
    view abstract10.1002/anie.202006122
  • Hydrothermal Stability of High-Surface-Area α-Al2O3and Its Use as a Support for Hydrothermally Stable Fischer-Tropsch Synthesis Catalysts
    Amrute, A.P. and Jeske, K. and Łodziana, Z. and Prieto, G. and Schüth, F.
    Chemistry of Materials 32 (2020)
    Nanocrystalline corundum synthesized by ball milling of boehmite is found to be exceptionally robust toward chemical weathering, a common problem of transition aluminas in different applications, most notably in the case of supported catalysts, which are exposed to hydrothermal reaction environments. Detailed characterization and surface cation coordination analysis indicate that the absence of tetrahedral Al species on corundum makes it stable toward chemical weathering. A cobalt catalyst developed using nano-α-Al2O3 as the support showed Fischer-Tropsch synthesis activity and selectivity comparable to the benchmark Co/γ-Al2O3 and remained stable over 250 h on-stream. Copyright © 2020 American Chemical Society.
    view abstract10.1021/acs.chemmater.0c01587
  • Insights into the mechanochemical synthesis of Sn-β: Solid-state metal incorporation in beta zeolite
    Joshi, H. and Ochoa-Hernández, C. and Nürenberg, E. and Kang, L. and Wang, F.R. and Weidenthaler, C. and Schmidt, W. and Schüth, F.
    Microporous and Mesoporous Materials 309 (2020)
    Sn-β zeolite is an active material for the isomerization of glucose to fructose, which is one of the critical reactions for the valorization of biomass. The material is synthesized either by a top-down or bottom-up approach. In this work, we use a top-down approach for the synthesis of Sn-β to incorporate the tin atoms into the *BEA framework. As compared to the literature, we replace the process of manual grinding with the use of ball milling to make the process reproducible, flexible, and scalable. The primary focus of this work is to investigate the processes occurring during the synthesis by a variety of characterization tools. These techniques include thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), physisorption, X-ray diffraction (XRD), and chemisorption monitored by Fourier-transform infrared spectroscopy (FTIR). The synthesis is followed by characterizing the material at various stages of synthesis. Finally, the materials are tested for the isomerization of glucose to fructose to assess the chemical nature of Sn-β zeolites. The results of this investigation provide several insights into the mechanochemical process for the incorporation of atoms in a zeolite framework. For instance, the importance of the size of precursors, distribution of Sn atoms during synthesis, and chemical changes occurring during milling are highlighted. These insights could produce a blueprint for the synthesis of a variety of solid catalysts. © 2020
    view abstract10.1016/j.micromeso.2020.110566
  • Iodine-Catalyzed Selective Functionalization of Ethane in Oleum: Toward a Direct Process for the Production of Ethylene Glycol from Shale Gas
    Bilke, M. and Zimmermann, T. and Schüth, F.
    Journal of the American Chemical Society 142 (2020)
    Direct valorization of ethane, a substantial component of shale gas deposits, at mild conditions remains a significant challenge, both from an industrial and an academic point of view. Herein, we report iodine as an efficient and selective catalyst for the functionalization of ethane in oleum at low temperatures and pressures. A thorough study of relevant reaction parameters revealed iodine to be remarkably more active than the previously reported "Periana/Catalytica"catalyst under optimized conditions. As a result of a fundamentally different catalytic cycle, iodine yields the bis-bisulfate ester of ethylene glycol (HO3SO-CH2-CH2-OSO3H, EBS), whereas for state-of-the-art platinum-based catalysts ethionic acid (HO3S-CH2-CH2-OSO3H, ETA) is obtained as the main product. Our findings open up an attractive route for the direct conversion of ethane toward ethylene glycol. © 2020 American Chemical Society.
    view abstract10.1021/jacs.0c08975
  • Mechanochemical Grafting: A Solvent-less Highly Efficient Method for the Synthesis of Hybrid Inorganic-Organic Materials
    Amrute, A.P. and Zibrowius, B. and Schüth, F.
    Chemistry of Materials 32 (2020)
    Solvent-free synthetic approaches are very attractive to curtail the chemical waste generation and simplify processes. Mechanochemistry has recently shown great potential in this direction. Here, we demonstrate the mechanochemical grafting for the synthesis of hybrid inorganic-organic materials in 5 min at room temperature without the use of any solvent. The mechanochemical functionalization of different solids (SBA-15, Î-Al2O3, SiO2 gel, and TiO2) with various organosilicon compounds (alkyltrialkoxysilanes or trialkylmonohalosilane) is confirmed by characterizing the resulting composite in detail by thermogravimetric analysis coupled to mass spectrometry, 29Si magic angle spinning nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy, which suggest the formation of chemical bonds between the solid surfaces and silanes. X-ray diffraction analysis shows that the original ordered mesoporous character of SBA-15 and crystalline structures of Î-Al2O3 or TiO2 are retained after grafting. N2 sorption evidences a decrease in specific surface areas, pore diameters, and pore volumes due to the silane functionalization. Our results show that the mechanochemical silylation is efficient and likely involves the direct condensation between alkoxy or halo groups of silane and surface hydroxyls of the solids. These results, providing a general, simple, highly efficient, and solvent-free alternative to solvothermal routes for the fabrication of hybrid materials, might lead to a new pathway for the preparation of different composites for various technological applications. Copyright © 2020 American Chemical Society.
    view abstract10.1021/acs.chemmater.0c01266
  • Response to Comment on "high-surface-area corundum by mechanochemically induced phase transformation of boehmite"
    Amrute, A.P. and Lodziana, Z. and Schreyer, H. and Weidenthaler, C. and Schüth, F.
    Science 368 (2020)
    Li et al. commented that our report claims that methods reported thus far cannot enable the production of high-purity corundum with surface areas greater than 100 m2g-1, and that our obtained material could be porous aggregates rather than nanoparticles. We disagree with both of these suggestions. © 2020 American Association for the Advancement of Science. All rights reserved.
    view abstract10.1126/science.abb0948
  • Walter Thiel (1949-2019)
    Fürstner, A. and List, B. and Ritter, T. and Schüth, F. and Neese, F.
    Angewandte Chemie (International ed. in English) 59 (2020)
    On August 23, 2019 Walter Thiel passed away suddenly and unexpectedly. Thiel was a giant in the field of Theoretical Chemistry and has left deep marks as an outstanding scientist and as a wonderful human being. With Walter Thiel, the scientific community has lost a visionary scientific leader and an important voice of reason. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201915463
  • Blending Real World Gasoline with Biofuel in a Direct Conversion Process
    Nürenberg, E. and Schulze, P. and Kohler, F. and Zubel, M. and Pischinger, S. and Schüth, F.
    ACS Sustainable Chemistry and Engineering 7 (2019)
    A method to produce the biofuel 2,5-dimethylfuran (DMF) from cellulose-derived 5-hydroxymethylfurfural (HMF) by hydrodeoxygenation (HDO) using commercial gasoline as solvent to obtain mixtures of gasoline with DMF, appropriate for direct use in present internal combustion engines, is presented. Best results were obtained with gasoline:ethanol mixtures in the ratio 9:1 (E10), as ethanol acts as a solvent mediator for the dissolution of HMF. Selected potential biofuels are also found to give high DMF yields, for example, several alcohols (81-92%) and 2-butanone (94%), while γ-valerolacton and saturated hydrocarbons show limitations (75% and 37%, respectively). The reaction in gasoline is conducted sequentially up to three times with an initial loading of 10 wt % HMF per step, resulting in a concentration increase of up to 7 wt % DMF for each step, by which a concentration range between 7 and 20 wt % DMF in the final blend is covered. The obtained blends were evaluated by the determination of the derived cetane number (DCN) and a simulated distillation with comparison to premixed blends and proved to be comparable in a wide concentration range of DMF (5-15 wt %). Thus, a potentially directly usable fuel blend is produced in a direct conversion process without the need of costly separation. Copyright © 2018 American Chemical Society.
    view abstract10.1021/acssuschemeng.8b03044
  • Direct, Selective Production of Aromatic Alcohols from Ethanol Using a Tailored Bifunctional Cobalt-Hydroxyapatite Catalyst
    Wang, Q.-N. and Weng, X.-F. and Zhou, B.-C. and Lv, S.-P. and Miao, S. and Zhang, D. and Han, Y. and Scott, S.L. and Schüth, F. and Lu, A.-H.
    ACS Catalysis 9 (2019)
    Aromatic alcohols are essential components of many solvents, coatings, plasticizers, fine chemicals, and pharmaceuticals. Traditional manufacturing processes involving the oxidation of petroleum-derived aromatic hydrocarbons suffer from low selectivity due to facile overoxidation reactions which produce aromatic aldehydes, acids, and esters. Here we report a Co-containing hydroxyapatite (HAP) catalyst that converts ethanol directly to methylbenzyl alcohols (MB-OH, predominantly 2-MB-OH) at 325 °C. The dehydrogenation of ethanol to acetaldehyde, which is catalyzed by Co2+, has the highest reaction barrier. Acetaldehyde undergoes rapid, HAP-catalyzed condensation and forms the key intermediate, 2-butenal, which yields aromatic aldehydes through self-condensation and then MB-OH via hydrogenation. In the presence of Co2+, 2-butenal is selectively hydrogenated to 2-butenol. This reaction does not hinder aromatization because cross-coupling between 2-butenal and 2-butenol leads directly to MB-OH without passing through MBâ•O. Using these insights a dual-bed catalyst configuration was designed for use in a single reactor to improve the aromatic alcohol selectivity. Its successful use supports the proposed reaction mechanism. Copyright © 2019 American Chemical Society.
    view abstract10.1021/acscatal.9b02566
  • Encapsulation of sub-micrometer sized zeolites by porous silica – towards a rational design strategy for functional yolk-shells
    Joshi, H. and Schmidt, W. and Schüth, F.
    Microporous and Mesoporous Materials (2019)
    Catalysis often requires spatial separation of active centres. In material science this translates to a challenge in the synthesis of such materials, namely core-shells. Yolk-shell materials, a type of core-shell materials, possess a void between the core and shell that can be advantageous in catalysis. Yolk-shell materials with zeolitic core have not been reported extensively, despite their potential applicability in catalysis. This stems from the non-spherical morphology and surface properties of the zeolites, which makes controlled coating without defects difficult. Herein, we report a strategy for the encapsulation of beta zeolite (HBEA) with disordered mesoporous silica shell (HBEA@void@mSiO 2 ). HBEA is chosen as the centre (yolk) due to its cuboidal shape. The process involves creation of two shells, (a) sacrificial shell composed of resorcinol and formaldehyde, and (b) mesoporous silica shell. The result is an organic@inorganic hybrid that is thermally treated to obtain the corresponding hybrid. Polyvinylpyrrolidone (PVP) is an important component of the synthesis which assists in obtaining a uniform coating around the core. Thorough morphological, structural, fractal and textural characterization of this material was performed by electron microscopy, XRD, SAXS and sorption techniques. The hybrid possesses a hierarchical structure with an increasing porosity and spatial isolation of the core by the presence of a void. The siliceous nature of HBEA@void@mSiO 2 also enables a post-synthesis treatment for functional modification with mercaptosilane groups. The synthesis process shown here is highly controllable and has laid a solid foundation for a generalized synthesis strategy to build functional yolk-shell materials based on zeolites. © 2019
    view abstract10.1016/j.micromeso.2019.03.013
  • High-surface-area corundum by mechanochemically induced phase transformation of boehmite
    Amrute, A.P. and Łodziana, Z. and Schreyer, H. and Weidenthaler, C. and Schüth, F.
    Science 366 (2019)
    In its nanoparticulate form, corundum (a-Al2O3) could lead to several applications. However, its production into nanoparticles (NPs) is greatly hampered by the high activation energy barrier for its formation from cubic close-packed oxides and the sporadic nature of its nucleation. We report a simple synthesis of nanometer-sized a-Al2O3 (particle diameter ~13 nm, surface areas ~140 m2 g-1) by the mechanochemical dehydration of boehmite (g-AlOOH) at room temperature. This transformation is accompanied by severe microstructural rearrangements and might involve the formation of rare mineral phases, diaspore and tohdite, as intermediates. Thermodynamic calculations indicate that this transformation is driven by the shift in stability from boehmite to a-Al2O3 caused by milling impacts on the surface energy. Structural water in boehmite plays a crucial role in generating and stabilizing a-Al2O3 NPs. © 2019 American Association for the Advancement of Science. All rights reserved.
    view abstract10.1126/science.aaw9377
  • Hydroxyapatite nanowires rich in [Ca-O-P] sites for ethanol direct coupling showing high C6-12 alcohol yield
    Wang, Q.-N. and Zhou, B.-C. and Weng, X.-F. and Lv, S.-P. and Schüth, F. and Lu, A.-H.
    Chemical Communications 55 (2019)
    Herein, we have shown that the [Ca-O-P] sites exposed on hydroxyapatite are clearly responsible for C-C formation in ethanol direct-coupling, and their high density accelerates the C-C coupling rate and boosts C6-12 alcohol production. Notably, nanowire-like hydroxyapatite exhibited 30.4% selectivity to n-butanol and 63.9% selectivity to C6-12OH at a conversion of 45.7% at 325 °C, and thereby close to 30% yield of C6-12OH, which is greatly higher than that using the state-of-the-art catalysts (6%). © 2019 The Royal Society of Chemistry.
    view abstract10.1039/c9cc05454e
  • Making more from methane
    Schüth, F.
    Science 363 (2019)
    view abstract10.1126/science.aaw7738
  • Methane to Chloromethane by Mechanochemical Activation: A Selective Radical Pathway
    Bilke, M. and Losch, P. and Vozniuk, O. and Bodach, A. and Schüth, F.
    Journal of the American Chemical Society 141 (2019)
    State-of-the-art processes to directly convert methane into CH3Cl are run under corrosive conditions and typically yield a mixture of chloromethanes requiring subsequent separation. We report a mechanochemical strategy to selectively convert methane to chloromethane under overall benign conditions, employing trichloroisocyanuric acid (TCCA) as a cheap and noncorrosive solid chlorinating agent. TCCA is shown to release active chlorine species upon milling with Lewis acids such as alumina and ceria to functionalize methane at moderate temperatures (<150 °C). A thorough parameter optimization led to a maximum methane chlorination rate of 0.8 μmol(CH4,conv) (g(catalyst) s)-1. Findings were compared to the thermal reaction of methane with TCCA and evidenced that mechanochemical activation permitted significantly lower reaction temperatures (90 vs 200 °C) at a drastically improved CH3Cl selectivity (95% vs 66% at 30% conversion). Considering the characterization of the interaction between TCCA and Lewis acids as well as the in-depth analysis of byproducts, we suggest a plausible reaction mechanism and a possible regeneration of the chlorinating agent.
    view abstract10.1021/jacs.9b04413
  • Milling Down to Nanometers: A General Process for the Direct Dry Synthesis of Supported Metal Catalysts
    Schreyer, H. and Eckert, R. and Immohr, S. and de Bellis, J. and Felderhoff, M. and Schüth, F.
    Angewandte Chemie - International Edition 58 (2019)
    Supported catalysts are among the most important classes of catalysts. They are typically prepared by wet-chemical methods, such as impregnation or co-precipitation. Here we disclose that dry ball milling of macroscopic metal powder in the presence of a support oxide leads in many cases to supported catalysts with particles in the nanometer size range. Various supports, including TiO2, Al2O3, Fe2O3, and Co3O4, and different metals, such as Au, Pt, Ag, Cu, and Ni, were studied, and for each of the supports and the metals, highly dispersed nanoparticles on supports could be prepared. The supported catalysts were tested in CO oxidation, where they showed activities in the same range as conventionally prepared catalysts. The method thus provides a simple and cost-effective alternative to the conventionally used impregnation methods. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201903545
  • Nanoporous carbon: Liquid-free synthesis and geometry-dependent catalytic performance
    Xu, R. and Kang, L. and Knossalla, J. and Mielby, J. and Wang, Q. and Wang, B. and Feng, J. and He, G. and Qin, Y. and Xie, J. and Swertz, A.-C. and He, Q. and Kegnæs, Sø. and Brett, D.J.L. and Schüth, F. and Wang, F.R.
    ACS Nano 13 (2019)
    Nanostructured carbons with different pore geometries are prepared with a liquid-free nanocasting method. The method uses gases instead of liquid to disperse carbon precursors, leach templates, and remove impurities, minimizing synthetic procedures and the use of chemicals. The method is universal and demonstrated by the synthesis of 12 different porous carbons with various template sources. The effects of pore geometries in catalysis can be isolated and investigated. Two of the resulted materials with different pore geometries are studied as supports for Ru clusters in the hydrogenolysis of 5-hydroxymethylfurfural (HMF) and electrochemical hydrogen evolution (HER). The porous carbon-supported Ru catalysts outperform commercial ones in both reactions. It was found that Ru on bottleneck pore carbon shows a highest yield in hydrogenolysis of HMF to 2,5-dimethylfuran (DMF) due to a better confinement effect. A wide temperature operation window from 110 to 140 °C, with over 75% yield and 98% selectivity of DMF, has been achieved. Tubular pores enable fast charge transfer in electrochemical HER, requiring only 16 mV overpotential to reach current density of 10 mA·cm-2. © 2019 American Chemical Society.
    view abstract10.1021/acsnano.8b09399
  • Tailoring the Surface Structure of Silicon Carbide Support for Copper Catalyzed Ethanol Dehydrogenation
    Li, M.-Y. and Lu, W.-D. and He, L. and Schüth, F. and Lu, A.-H.
    ChemCatChem 11 (2019)
    The production of acetaldehyde through biomass-derived ethanol dehydrogenation is a sustainable alternative compared to the fossil-feedstock based process, for which Cu-based catalysts are considered to be the most efficient. Herein, we modified the surface of silicon carbide (SiC) to alter the properties of the interface from SiO2-rich to C-rich, and we prepared a series of Cu-supported catalysts (Cu/SiC, Cu/SiO2/SiC, and Cu/C/SiC) with the aim of insight into the effect of the interface structure and composition on catalytic dehydrogenation of ethanol. At 280 °C, the Cu/SiO2/SiC catalyst exhibits high ethanol conversion due to the excellent dispersion of Cu nanoparticles promoted by SiO2-rich interface. In contrast, Cu nanoparticles dispersed on C/SiC shows somewhat lower activity but excellent acetaldehyde selectivity with trace amounts of by-products under identical reaction conditions. This difference is attributed to the fast removal of acetaldehyde because of its low affinity for the relatively inert C-rich interface (C/SiC). This work provides an in-depth understanding of Cu−Si−C multi-interfacial structure and the ethanol dehydrogenation behavior, which may shed light on the design of novel catalysts with tailored interfacial structures. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/cctc.201801742
  • Towards maximized utilization of iridium for the acidic oxygen evolution reaction
    Ledendecker, M. and Geiger, S. and Hengge, K. and Lim, J. and Cherevko, S. and Mingers, A.M. and Göhl, D. and Fortunato, G.V. and Jalalpoor, D. and Schüth, F. and Scheu, C. and Mayrhofer, K.J.J.
    Nano Research 12 (2019)
    The reduction in noble metal content for efficient oxygen evolution catalysis is a crucial aspect towards the large scale commercialisation of polymer electrolyte membrane electrolyzers. Since catalytic stability and activity are inversely related, long service lifetime still demands large amounts of low-abundant and expensive iridium. In this manuscript we elaborate on the concept of maximizing the utilisation of iridium for the oxygen evolution reaction. By combining different tin oxide based support materials with liquid atomic layer deposition of iridium oxide, new possibilities are opened up to grow thin layers of iridium oxide with tuneable noble metal amounts. In-situ, time- and potential-resolved dissolution experiments reveal how the stability of the substrate and the catalyst layer thickness directly affect the activity and stability of deposited iridium oxide. Based on our results, we elaborate on strategies how to obtain stable and active catalysts with maximized iridium utilisation for the oxygen evolution reaction and demonstrate how the activity and durability can be tailored correspondingly. Our results highlight the potential of utilizing thin noble metal films with earth abundant support materials for future catalytic applications in the energy sector. [Figure not available: see fulltext.]. © 2019, The author(s).
    view abstract10.1007/s12274-019-2383-y
  • Wilhelm Keim (1934-2018)
    Schüth, F. and Wasserscheid, P.
    Angewandte Chemie (International ed. in English) 58 (2019)
    Wilhelm "Willi" Keim, professor emeritus at the RWTH Aachen University, passed away on September 30, 2018. Keim was best known for his role in developing the Shell higher olefins process (SHOP), and also made pioneering contributions to the areas of liquid-liquid biphasic catalysis, and green and sustainable chemistry. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201812688
  • Common Pitfalls of Catalysis Manuscripts Submitted to Chemistry of Materials
    Schüth, F. and Ward, M.D. and Buriak, J.M.
    Chemistry of Materials 30 (2018)
    There are certainly many more pitfalls in analyzing and reporting catalysis work, but based on our experience, the points above represent a large majority of the technical flaws in manuscripts submitted to Chemistry of Materials in the field of catalysis. Proper reporting according to the advice above will reduce the frustration of editors, reviewers and authors, leading to a more streamlined publishing experience. © 2018 American Chemical Society.
    view abstract10.1021/acs.chemmater.8b01831
  • Copper Supported on Hybrid C@SiO2 Hollow Submicron Spheres as Active Ethanol Dehydrogenation Catalyst
    Lu, W.-D. and Wang, Q.-N. and He, L. and Li, W.-C. and Schüth, F. and Lu, A.-H.
    ChemNanoMat 4 (2018)
    The dehydrogenation of ethanol to acetaldehyde (DHEA) is an environmentally benign alternative for synthetic chemistry and for the fine chemical industry. The key is to design Cu-based catalysts with certain structures to obtain high acetaldehyde selectivity. Herein, hybrid C@SiO2 hollow submicron spheres were designed and synthesized using a confined pyrolysis method. This hybrid structure processes a layer of carbon-silica hybrid shell. After loading the Cu, the Cu/C@SiO2 catalyst exhibited 36.1% conversion of ethanol and ∼99% acetaldehyde selectivity at 260 °C. The hybrid support combined the two favorable properties of carbon and silica and thus improving both selectivity and stability. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/cnma.201800021
  • Cu supported on thin carbon layer-coated porous SiO2 for efficient ethanol dehydrogenation
    Wang, Q.-N. and Shi, L. and Li, W. and Li, W.-C. and Si, R. and Schüth, F. and Lu, A.-H.
    Catalysis Science and Technology 8 (2018)
    We report a designed Cu/C/SiO2 composite catalyst, which shows a high acetaldehyde selectivity (up to ∼98%) and good stability for a 60 h test at 260 °C in ethanol dehydrogenation. Various characterization techniques demonstrate that the carbon covers the Si-OH groups on silica and promotes the reduction of Cu+ to Cu0. This reduces the concentration of active sites for secondary reactions of CH3CHO, which leads to a high initial selectivity (∼93%) as compared to that of Cu/SiO2 (∼76%). Moreover, the chemical interaction between Cu and SiO2 of the C/SiO2 support, verified by X-ray photoelectron spectroscopy, enhances the interaction between the metal and the support and thus contributes to prevention of the agglomeration of Cu particles, which is the reason for the good catalytic stability of Cu/C/SiO2. Thus, this study is an example of how careful design of the catalyst can strongly improve the catalytic performance. © 2018 The Royal Society of Chemistry.
    view abstract10.1039/c7cy02057k
  • Electrochemical stability of hexagonal tungsten carbide in the potential window of fuel cells and water electrolyzers investigated in a half-cell configuration
    Göhl, D. and Mingers, A.M. and Geiger, S. and Schalenbach, M. and Cherevko, S. and Knossalla, J. and Jalalpoor, D. and Schüth, F. and Mayrhofer, K.J.J. and Ledendecker, M.
    Electrochimica Acta 270 (2018)
    Tungsten carbide has attracted much interest as possible support for oxygen reduction and hydrogen oxidation in fuel cells and as catalyst itself for the hydrogen evolution reaction in water electrolyzers in the last years. Herein, we investigate the dissolution behavior of hexagonal tungsten carbide in acidic media with cyclovoltammetric and galvanostatic procedures under steady-state and dynamic conditions. The tungsten dissolution rate in the electrolyte was monitored in-situ and time resolved via coupling of the scanning flow cell with an inductively coupled plasma mass spectrometer (SFC-ICP-MS), allowing a direct correlation of potential and amount of dissolved species. The stability and passivation behavior of tungsten carbide was compared to pristine tungsten metal and its highest oxide WO3 in fuel cell/electrolyzer relevant potential ranges. It was found that partial passivation in the oxygen reduction region takes place, accompanied by steady dissolution of tungsten slightly above these potentials. In the HER/HOR region, no significant dissolution was observed. The dissolution rate of WC at high potentials was found to be in many cases almost one order of magnitude lower than for the pristine metal, yet two orders of magnitude higher than for its corresponding highest oxide. © 2018 Elsevier Ltd
    view abstract10.1016/j.electacta.2018.02.129
  • High surface area black TiO2 templated from ordered mesoporous carbon for solar driven hydrogen evolution
    Xiong, Y. and Gu, D. and Deng, X. and Tüysüz, H. and van Gastel, M. and Schüth, F. and Marlow, F.
    Microporous and Mesoporous Materials 268 (2018)
    Hydrogen reduction of TiO2 to generate surface Ti3+ can significantly increase the photochemical activity under solar-light illumination. However, the low surface areas of commercial TiO2 limit their photocatalytic activities. Herein, we report a high surface area ordered mesoporous black TiO2, which exhibits an improved photocatalytic performance. The TiO2 material was prepared by using a highly ordered mesoporous carbon CMK-3 as a hard template, which possesses very high surface area, large pore volume and uniform mesopores. By using the advantage of pore confinement in the mesoporous carbon template, TiO2-carbon composites were annealed at different temperatures to investigate the influence of the crystallinity of TiO2 on the photocatalytic hydrogen production. TiO2 calcined at 500 °C, having a high surface area (up to 158 m2 g−1), large pore volume (up to 0.62 cm3 g−1), uniform pore size (5–6 nm), and anatase crystal structure, indicated the highest hydrogen generation rate. Since the TiO2 has been treated at a higher temperature in the confinement of the mesoporous carbon, the TiO2 can easily be reduced at 500 °C under hydrogen atmosphere to generate surface Ti3+ species without destruction of the mesostructure and exhibits a high solar-driven hydrogen evolution rate (188 μmol h−1), which is more than two times higher than that of commercial TiO2 (82 μmol h−1). © 2018 Elsevier Inc.
    view abstract10.1016/j.micromeso.2018.04.018
  • Impact of Hydrophobic Organohybrid Silicas on the Stability of Ni2P Catalyst Phase in the Hydrodeoxygenation of Biophenols
    Dierks, M. and Cao, Z. and Manayil, J.C. and Akilavasan, J. and Wilson, K. and Schüth, F. and Rinaldi, R.
    ChemCatChem 10 (2018)
    Hydrodeoxygenation (HDO) of lignocellulose-derived pyrolysis oils offers an option to produce fuel substitutes. However, catalyst deactivation and stability constitute a significant issue. Herein, the dependence of stability and activity of Ni2P/SiO2 HDO catalysts on the support surface polarity is addressed in detail. The support surface polarity was adjusted by copolymerizing tetraethyl orthosilicate (TEOS) with different types and amounts of organosilanes by a sol–gel process in the presence of nickel nitrate and citric acid. After thermal treatment under an inert atmosphere, Ni/SiO2 precursors were formed. They were converted into Ni2P/SiO2 catalysts by using NaH2PO2 as a PH3 source. The catalyst surface polarity was characterized by inverse gas chromatography measurements of the free energy of methanol adsorption, and specific and dispersive surface energies derived from polar and nonpolar probe molecule adsorption. The correlation between catalyst performance and support surface polarity indicates that, to prevent deactivation of the catalyst by water under reaction conditions, the affinity of the support towards polar substances must be decreased below a threshold value. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/cctc.201702001
  • Influence of preparation method and doping of zirconium oxide onto the material characteristics and catalytic activity for the HDO reaction in nickel on zirconium oxide catalysts
    Pichler, C.M. and Gu, D. and Joshi, H. and Schüth, F.
    Journal of Catalysis 365 (2018)
    Different Ni/ZrO2 catalysts were prepared and tested for the hydrodeoxygenation (HDO) reaction of guaiacol. It was shown that the preparation mode of the ZrO2 support has a significant influence on the catalytic results, as remaining elements like Si and Na from the preparation can change the material properties. The influence of Si and Na onto these material properties, which were especially surface acidity and oxygen vacancy concentration, could be clarified. It could be also rationalized, how the change of these properties affects the results of the HDO reaction. Furthermore, it was demonstrated that the oxygen vacancy concentration is an important factor for the catalytic performance, although this property has hardly been considered in the design of HDO catalysts so far. La doping was found to be an efficient strategy to tune the oxygen vacancy concentration, and by using this approach the catalytic performance of the catalyst could be improved remarkably. © 2018
    view abstract10.1016/j.jcat.2018.07.021
  • Monitoring the formation of PtNi nanoalloys supported on hollow graphitic spheres using: In situ pair distribution function analysis
    Ortatatli, Ş. and Knossalla, J. and Schüth, F. and Weidenthaler, C.
    Physical Chemistry Chemical Physics 20 (2018)
    This article aims to address the formation and the structural disordering/ordering phenomena of PtNi nanoalloys supported on hollow graphitic spheres (HGSs) using pair distribution function (PDF) analysis under ex situ/in situ data collection conditions. Starting from small nanoparticles (10-15 Å in diameter) embedded in HGSs, structural changes were monitored during stepwise heating and cooling of the sample using in situ PDF analysis. In order to evaluate the conventional synthesis route for the production of PtNi nanoalloys supported on HGSs, ex situ PDF experiments were performed before and after heat treatment in a furnace. The studies demonstrate that the local structure of the in situ synthesised PtNi nanoalloy differs from its ex situ synthesised counterpart. A partially ordered PtNi nanoalloy was obtained during the stepwise in situ cooling of the precursor, whereas the conventional ex situ synthesis route did not lead to the formation of an ordered crystal structure. In this study we could show that rapid heating and cooling results in a disordered PtNi alloy whereas slow heating and cooling leads to disorder-order transitions in PtNi. © 2018 the Owner Societies.
    view abstract10.1039/c7cp07840d
  • Scalable One-Pot Synthesis of Yolk-Shell Carbon Nanospheres with Yolk-Supported Pd Nanoparticles for Size-Selective Catalysis
    Wang, G.-H. and Chen, K. and Engelhardt, J. and Tüysüz, H. and Bongard, H.-J. and Schmidt, W. and Schüth, F.
    Chemistry of Materials 30 (2018)
    view abstract10.1021/acs.chemmater.8b00456
  • Avoiding Self-Poisoning: A Key Feature for the High Activity of Au/Mg(OH)2 Catalysts in Continuous Low-Temperature CO Oxidation
    Wang, Y. and Widmann, D. and Lehnert, F. and Gu, D. and Schüth, F. and Behm, R.J.
    Angewandte Chemie - International Edition 56 (2017)
    Au/Mg(OH)2 catalysts have been reported to be far more active in the catalytic low-temperature CO oxidation (below 0 °C) than the thoroughly investigated Au/TiO2 catalysts. Based on kinetic and in situ infrared spectroscopy (DRIFTS) measurements, we demonstrate that the comparatively weak interaction of Au/Mg(OH)2 with CO2 formed during the low-temperature reaction is the main reason for the superior catalyst performance. This feature enables rapid product desorption and hence continuous CO oxidation at temperatures well below 0 °C. At these temperatures, Au/TiO2 also catalyzes CO2 formation, but does not allow for CO2 desorption, which results in self-poisoning. At higher temperatures (above 0 °C), however, CO2 formation is rate-limiting, which results in a much higher activity for Au/TiO2 under these reaction conditions. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201702178
  • Bio-oil upgrading via vapor-phase ketonization over nanostructured FeOx and MnOx: catalytic performance and mechanistic insight
    Heracleous, E. and Gu, D. and Schüth, F. and Bennett, J.A. and Isaacs, M.A. and Lee, A.F. and Wilson, K. and Lappas, A.A.
    Biomass Conversion and Biorefinery 7 (2017)
    In this study, nanostructured FeOx and MnOx were prepared by two synthetic routes, nanocasting and hydrothermal, and evaluated for bio-oil upgrading via vapor-phase ketonization. Catalytic performance measurements in the ketonization of representative model compounds, acetic and propionic acid, at 335 °C showed high activity for the hydrothermal MnOx and nanocast FeOx (conversion &gt;90%) with high selectivity to the respective ketones. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies followed by temperature-programmed thermogravimetric analysis (TGA) and MS showed that the reactive intermediates are bidentate acetate species that desorb as acetone over FeOx and unreacted acetic acid over MnOx (in contradiction to its associated catalysis). Powder X-ray diffraction and X-ray photoelectron spectroscopy analysis of used samples revealed that MnO2 was reduced to MnO during reaction. The relative surface concentrations of adsorbed acetate for the used MnOx catalysts (from DRIFTS) correlated with their corresponding acetic acid conversion (from ketonization studies), indicating that MnO is the active phase for acetic acid ketonization, with MnO2 a precursor which is reduced in situ at temperatures &gt;300 °C. Vapor-phase ketonization of the aqueous phase of a real thermal bio-oil, produced from the fast pyrolysis of lignocellulosic biomass, was demonstrated successfully over MnOx prepared by the hydrothermal route, highlighting this as an attractive approach for the upgrading of pyrolysis bio-oils. © 2017, Springer-Verlag Berlin Heidelberg.
    view abstract10.1007/s13399-017-0268-4
  • Catalysis Meets Nonthermal Separation for the Production of (Alkyl)phenols and Hydrocarbons from Pyrolysis Oil
    Cao, Z. and Engelhardt, J. and Dierks, M. and Clough, M.T. and Wang, G.-H. and Heracleous, E. and Lappas, A. and Rinaldi, R. and Schüth, F.
    Angewandte Chemie - International Edition 56 (2017)
    A simple and efficient hydrodeoxygenation strategy is described to selectively generate and separate high-value alkylphenols from pyrolysis bio-oil, produced directly from lignocellulosic biomass. The overall process is efficient and only requires low pressures of hydrogen gas (5 bar). Initially, an investigation using model compounds indicates that MoCx/C is a promising catalyst for targeted hydrodeoxygenation, enabling selective retention of the desired Ar−OH substituents. By applying this procedure to pyrolysis bio-oil, the primary products (phenol/4-alkylphenols and hydrocarbons) are easily separable from each other by short-path column chromatography, serving as potential valuable feedstocks for industry. The strategy requires no prior fractionation of the lignocellulosic biomass, no further synthetic steps, and no input of additional (e.g., petrochemical) platform molecules. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201610405
  • Hands-on Guide to the Synthesis of Mesoporous Hollow Graphitic Spheres and Core-Shell Materials
    Knossalla, J. and Jalalpoor, D. and Schüth, F.
    Chemistry of Materials 29 (2017)
    In this work we present a detailed preparation method for mesoporous hollow graphitic spheres (HGS) that has been developed in our laboratory over recent years. The aim of this description is to enable the reader to reproduce the procedure by highlighting important steps, conditions, and challenges during the synthesis. HGS have initially been developed as a carbon support to enhance the stability of metal catalysts in the oxygen reduction reaction (ORR) of PEM fuel cells via pore confinement. The HGS are synthesized in a multistep procedure employing a core-shell silica template, DVB as carbon source, and iron as graphitization catalyst. The silica template is removed by leaching with hydrofluoric acid yielding the mesoporous carbon support, where metal catalysts can be introduced via incipient wetness method followed by a reduction in hydrogen. The whole procedure allows high control over product parameters such as core or shell diameter and graphitization degree. Thus, it can be adapted and tuned to match the desired properties of high performance materials for various potential applications. © 2017 American Chemical Society.
    view abstract10.1021/acs.chemmater.7b02645
  • High activity and negative apparent activation energy in low-temperature CO oxidation - Present on Au/Mg(OH)2, absent on Au/TiO2
    Wang, Y. and Widmann, D. and Wittmann, M. and Lehnert, F. and Gu, D. and Schüth, F. and Behm, R.J.
    Catalysis Science and Technology 7 (2017)
    Aiming at a better understanding of the unusual low-temperature CO oxidation reaction behavior on Au/Mg(OH)2 catalysts, we investigated this reaction mainly by combined kinetic and in situ IR spectroscopy measurements over a wide range of temperatures, from -90 °C to 200 °C. Catalysts with a very narrow Au particle size distribution were prepared by colloidal deposition. Kinetic measurements, performed under differential, dry reaction conditions at different constant temperatures, enabled the separation of thermal and deactivation effects. They revealed that the distinct reaction behavior, with an exceptionally high activity at temperatures below 0 °C and decreasing CO oxidation rates in the range between -50 °C and 30 °C, equivalent to a negative apparent activation energy, does not result from either deactivation effects or H2O trace impurities, but is an intrinsic feature of the reaction. An unusual temperature dependence was also observed for the tendency for deactivation, with a pronounced maximum at -20 °C, which mainly results from an accumulation of surface carbonate species blocking active reaction sites or access of adsorbed reactants to them. Similar measurements on Au/TiO2 catalysts revealed that the high activity of Au/Mg(OH)2 in the low-temperature range compared to Au/TiO2 is first of all due to the weaker interactions of Mg(OH)2 with CO2 compared to TiO2. This leads to an increasing tendency of CO2 product molecules to adsorb on the latter catalyst at reaction temperatures below 0 °C and hence to rapid 'self-poisoning' with CO2 desorption as the rate-limiting step. For Au/Mg(OH)2, CO2 desorption is much faster, allowing much higher rates in the continuous CO oxidation. Based on temporal analysis of products (TAP) reactor measurements, the decay of the reaction rates in the range -50 °C to +50 °C is tentatively attributed to a decreasing steady-state coverage of weakly bound molecularly adsorbed O2 with increasing temperature, while stable adsorbed active surface oxygen is negligible over the entire range of reaction temperatures investigated. The implications of these and earlier findings for the mechanistic understanding of the low-temperature CO oxidation on Au/Mg(OH)2 and support effects therein are discussed. © The Royal Society of Chemistry 2017.
    view abstract10.1039/c7cy00722a
  • Intermediate Product Regulation in Tandem Solid Catalysts with Multimodal Porosity for High-Yield Synthetic Fuel Production
    Duyckaerts, N. and Bartsch, M. and Trotuş, I.-T. and Pfänder, N. and Lorke, A. and Schüth, F. and Prieto, G.
    Angewandte Chemie - International Edition 56 (2017)
    Tandem catalysis is an attractive strategy to intensify chemical technologies. However, simultaneous control over the individual and concerted catalyst performances poses a challenge. We demonstrate that enhanced pore transport within a Co/Al2O3 Fischer–Tropsch (FT) catalyst with hierarchical porosity enables its tandem integration with a Pt/ZSM-5 zeolitic hydrotreating catalyst in a spatially distant fashion that allows for catalyst-specific temperature adjustment. Nevertheless, this system resembles the case of close active-site proximity by mitigating secondary reactions of primary FT α-olefin products. This approach enables the combination of in situ dewaxing with a minimum production of gaseous hydrocarbons (18 wt %) and an up to twofold higher (50 wt %) selectivity to middle distillates compared to tandem pairs based on benchmark mesoporous FT catalysts. An overall 80 % selectivity to liquid hydrocarbons from syngas is attained in one step, attesting to the potential of this strategy for increasing the carbon efficiency in intensified gas-to-liquid technologies. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201705714
  • Oscillatory combustion of propene during in situ mechanical activation of solid catalysts
    Schreyer, H. and Immohr, S. and Schüth, F.
    Journal of Materials Science 52 (2017)
    Mechanochemical activation of solids can lead to a strong increase in their activity as catalysts in heterogeneously catalyzed reactions. In the following, we report on the effects of solid catalyst activation during ball milling that lead to oscillatory behavior in CO and CO2 formation during propene oxidation. The oscillations arise under in situ ball milling conditions over chromium(III) oxide (Cr2O3) and cerium(IV) oxide (CeO2), respectively. The experiments were conducted under continuous gas flow at ambient pressure and temperature, using both a modified steel and a tungsten carbide milling vessel. Abrasion of particles from the steel milling vessel could be eliminated as the sole cause for the oscillations through substitution by a tungsten carbide milling vessel. The intensity and frequency of oscillations are shown to be dependent on the propene-to-oxygen ratio, the milling frequency, milling ball size and metal oxide used. Overall, Cr2O3 shows higher activity for oscillatory propene combustion under in situ mechanical activation than CeO2. © 2017, The Author(s).
    view abstract10.1007/s10853-017-1153-z
  • Preferential Carbon Monoxide Oxidation over Copper-Based Catalysts under In Situ Ball Milling
    Eckert, R. and Felderhoff, M. and Schüth, F.
    Angewandte Chemie - International Edition 56 (2017)
    In situ ball milling of solid catalysts is a promising yet almost unexplored concept for boosting catalytic performance. The continuous preferential oxidation of CO (CO-PROX) under in situ ball milling of Cu-based catalysts such as Cu/Cr2O3 is presented. At temperatures as low as −40 °C, considerable activity and more than 95 % selectivity were achieved. A negative apparent activation energy was observed, which is attributed to the mechanically induced generation and subsequent thermal healing of short-lived surface defects. In situ ball milling at sub-zero temperatures resulted in an increase of the CO oxidation rate by roughly 4 orders of magnitude. This drastic and highly selective enhancement of CO oxidation showcases the potential of in situ ball milling in heterogeneous catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201610501
  • Selective glycerol oxidation over ordered mesoporous copper aluminum oxide catalysts
    Schünemann, S. and Schüth, F. and Tüysüz, H.
    Catalysis Science and Technology 7 (2017)
    Glycerol is a major by-product of the biodiesel production and is therefore produced in high quantities. While currently there are limited possible applications for this highly functionalized molecule, glycerol can be a cheap and abundant feedstock for value-added products that are accessible by selective oxidation. Usually, the selective oxidation of glycerol utilizes expensive noble metal catalysts, such as Au, Pt, and Pd. Here we report the selective oxidation of glycerol in basic media, using ordered mesoporous Cu-Al2O3 catalysts with various Cu loadings prepared by a facile soft-templating method. The materials were characterized in detail by nitrogen physisorption, vis-NIR spectroscopy, EDX, low- and wide-angle XRD, XPS, and TEM. Subsequently the reaction conditions for glycerol oxidation were optimized. The catalytic oxidation of glycerol yields C3 products, such as glyceric acid and tartronic acid, and also C2 and C1 products, such as glycolic acid, oxalic acid, and formic acid. Moreover, the role of the solvent on the catalytic reaction was investigated, and the addition of various co-solvents to the aqueous reaction mixture was found to increase the initial reaction rate up to a factor of three. The trends of the initial reaction rates correlate well with the polarity of the water/co-solvent mixtures. The prepared Cu-Al2O3 catalysts are a more cost-efficient and environmentally viable alternative to the reported noble metal catalysts. © 2017 The Royal Society of Chemistry.
    view abstract10.1039/c7cy01451a
  • Surface-Casting Synthesis of Mesoporous Zirconia with a CMK-5-Like Structure and High Surface Area
    Gu, D. and Schmidt, W. and Pichler, C.M. and Bongard, H.-J. and Spliethoff, B. and Asahina, S. and Cao, Z. and Terasaki, O. and Schüth, F.
    Angewandte Chemie - International Edition (2017)
    About 15years ago, the Ryoo group described the synthesis of CMK-5, a material consisting of a hexagonal arrangement of carbon nanotubes. Extension of the surface casting synthesis to oxide compositions, however, was not possible so far, in spite of many attempts. Here it is demonstrated, that crystalline mesoporous hollow zirconia materials with very high surface areas up to 400m2g-1, and in selected cases in the form of CMK-5-like, are indeed accessible via such a surface casting process. The key for the successful synthesis is an increased interaction between the silica hard template surface and the zirconia precursor species by using silanol group-rich mesoporous silica as a hard template. The surface areas of the obtained zirconias exceed those of conventionally hard-templated ones by a factor of two to three. The surface casting process seems to be applicable also to other oxide materials. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201705042
  • The Influence of Water on the Performance of Molybdenum Carbide Catalysts in Hydrodeoxygenation Reactions: A Combined Theoretical and Experimental Study
    Engelhardt, J. and Lyu, P. and Nachtigall, P. and Schüth, F. and García, Á.M.
    ChemCatChem 9 (2017)
    Understanding the deactivation of transition-metal carbide catalysts during hydrodeoxygenation (HDO) reactions is of great importance for improving the production of the second generation fuels from biomass. Based on a combined experimental and theoretical study, we present a mechanistic model for the deactivation of molybdenum carbide catalysts during phenol HDO in the presence of water. At increased water pressure, water molecules preferentially bind to the surface, and active sites are no longer accessible for phenol. In line with first principle calculations, experiments reveal that this process is fully reversible because the reduction of the water partial pressure results in a threefold increase in conversion. The direct deoxygenation of phenol was calculated to be the most favorable pathway, which is governed by the structure of the phenol adsorption complex on the surface at high hydrogen coverage. This is consistent with the experimentally observed high benzene selectivity (85 %) for phenol HDO over MoCx/HCS (hollow carbon spheres) catalyst. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/cctc.201700181
  • The Space Confinement Approach Using Hollow Graphitic Spheres to Unveil Activity and Stability of Pt-Co Nanocatalysts for PEMFC
    Pizzutilo, E. and Knossalla, J. and Geiger, S. and Grote, J.-P. and Polymeros, G. and Baldizzone, C. and Mezzavilla, S. and Ledendecker, M. and Mingers, A. and Cherevko, S. and Schüth, F. and Mayrhofer, K.J.J.
    Advanced Energy Materials 7 (2017)
    The performance of polymer electrolyte fuel cells is strongly correlated to the electrocatalytic activity and stability. In particular, the latter is the result of an interplay between different degradation mechanisms. The essential high stability, demanded for real applications, requires the synthesis of advanced electrocatalysts that withstand the harsh operation conditions. In the first part of this study, the synthesis of oxygen reduction electrocatalysts consisting of Pt-Co (i.e., Pt5Co, Pt3Co, and PtCo) alloyed nanoparticles encapsulated in the mesoporous shell of hollow graphitic spheres (HGS) is reported. The mass activities of the activated catalysts depend on the initial alloy composition and an activity increase on the order of two to threefold, compared to pure Pt@HGS, is achieved. The key point of the second part is the investigation of the degradation of PtCo@HGS (showing the highest activity). Thanks to pore confinement, the impact of dissolution/dealloying and carbon corrosion can be studied without the interplay of other degradation mechanisms that would induce a substantial change in the particle size distribution. Therefore, impact of the upper potential limit and the scan rates on the dealloying and electrochemical surface area evolution can be examined in detail. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/aenm.201700835
  • A Vibrant Science Lives from Within
    Schüth, F.
    Angewandte Chemie - International Edition 55 (2016)
    view abstract10.1002/anie.201609519
  • Co3O4 Nanoparticles Supported on Mesoporous Carbon for Selective Transfer Hydrogenation of α,β-Unsaturated Aldehydes
    Wang, G.-H. and Deng, X. and Gu, D. and Chen, K. and Tüysüz, H. and Spliethoff, B. and Bongard, H.-J. and Weidenthaler, C. and Schmidt, W. and Schüth, F.
    Angewandte Chemie - International Edition 55 (2016)
    A simple and scalable method for synthesizing Co3O4nanoparticles supported on the framework of mesoporous carbon (MC) was developed. Benefiting from an ion-exchange process during the preparation, the cobalt precursor is introduced into a mesostructured polymer framework that results in Co3O4nanoparticles (ca. 3 nm) supported on MC (Co3O4/MC) with narrow particle size distribution and homogeneous dispersion after simple reduction/pyrolysis and mild oxidation steps. The as-obtained Co3O4/MC is a highly efficient catalyst for transfer hydrogenation of α,β-unsaturated aldehydes. Selectivities towards unsaturated alcohols are always higher than 95 % at full conversion. In addition, the Co3O4/MC shows high stability under the reaction conditions, it can be recycled at least six times without loss of activity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201604673
  • Continuous synthesis of nanostructured silica based materials in a gas-liquid segmented flow tubular reactor
    Knossalla, J. and Mezzavilla, S. and Schüth, F.
    New Journal of Chemistry 40 (2016)
    A continuous synthesis of several spherical silica structures-by means of a gas-liquid segmented flow tubular reactor-is reported. Specifically, as proof of concept, we showed that 300-400 nm mesoporous core-shell spheres (SiO2@mSiO2), mesoporous spheres (mSiO2) as well gold-encapsulated spheres (Au@SiO2) can be effectively produced in a continuous manner in a tubular reactor. Thus, the successful conversion of classical batch methods to continuous processes opens new possibilities for the up-scaled synthesis of advanced nanostructured materials. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2016.
    view abstract10.1039/c5nj03033a
  • Gold on Different Manganese Oxides: Ultra-Low-Temperature CO Oxidation over Colloidal Gold Supported on Bulk-MnO2 Nanomaterials
    Gu, D. and Tseng, J.-C. and Weidenthaler, C. and Bongard, H.-J. and Spliethoff, B. and Schmidt, W. and Soulimani, F. and Weckhuysen, B.M. and Schüth, F.
    Journal of the American Chemical Society 138 (2016)
    Nanoscopic gold particles have gained very high interest because of their promising catalytic activity for various chemicals reactions. Among these reactions, low-temperature CO oxidation is the most extensively studied one due to its practical relevance in environmental applications and the fundamental problems associated with its very high activity at low temperatures. Gold nanoparticles supported on manganese oxide belong to the most active gold catalysts for CO oxidation. Among a variety of manganese oxides, Mn2O3 is considered to be the most favorable support for gold nanoparticles with respect to catalytic activity. Gold on MnO2 has been shown to be significantly less active than gold on Mn2O3 in previous work. In contrast to these previous studies, in a comprehensive study of gold nanoparticles on different manganese oxides, we developed a gold catalyst on MnO2 nanostructures with extremely high activity. Nanosized gold particles (2-3 nm) were supported on α-MnO2 nanowires and mesoporous β-MnO2 nanowire arrays. The materials were extremely active at very low temperature (-80 °C) and also highly stable at 25 °C (70 h) under normal conditions for CO oxidation. The specific reaction rate of 2.8 molCO·h-1·gAu -1 at a temperature as low as -85 °C is almost 30 times higher than that of the most active Au/Mn2O3 catalyst. © 2016 American Chemical Society.
    view abstract10.1021/jacs.6b04251
  • High temperature stability study of carbon supported high surface area catalysts—Expanding the boundaries of ex-situ diagnostics
    Polymeros, G. and Baldizzone, C. and Geiger, S. and Grote, J.P. and Knossalla, J. and Mezzavilla, S. and Keeley, G.P. and Cherevko, S. and Zeradjanin, A.R. and Schüth, F. and Mayrhofer, K.J.J.
    Electrochimica Acta 211 (2016)
    The performance of proton-exchange membrane fuel cells (PEMFCs) is defined by the equally important parameters of the intrinsic activity and stability of the electrocatalysts. This work focuses on the stability of carbon supported high surface area oxygen reduction reaction catalysts at potentials and temperatures similar to the operating conditions of PEMFCs. The catalysts used for this investigation consist of Pt nanoparticles of the same particle size supported on two types of carbon support having different textural properties, i.e., Vulcan and Hollow Graphitic Spheres (HGS). A broad toolbox of characterization techniques is utilized at 60 °C in order to resolve the contribution of the different degradation mechanisms, namely nanoparticle coalescence, metal dissolution and the corrosion of carbon support, to the total active surface area loss. The results obtained by investigating the impact of temperature, potential treatment and catalyst layer morphology on the aging behavior lead to a deeper understanding of the aging mechanisms and their interrelation at application-relevant conditions. Moreover, the previously reported improved performance of the Pt/HGS catalyst is confirmed also under higher temperatures. The experimental approach introduced in this work, highlights new challenges for high-temperature degradation investigations with supported PEMFC catalyst. © 2016 Elsevier Ltd
    view abstract10.1016/j.electacta.2016.06.105
  • Hollow Nano- and Microstructures as Catalysts
    Prieto, G. and Tüysüz, H. and Duyckaerts, N. and Knossalla, J. and Wang, G.-H. and Schüth, F.
    Chemical Reviews 116 (2016)
    Catalysis is at the core of almost every established and emerging chemical process and also plays a central role in the quest for novel technologies for the sustainable production and conversion of energy. Particularly since the early 2000s, a great surge of interest exists in the design and application of micro- and nanometer-sized materials with hollow interiors as solid catalysts. This review provides an updated and critical survey of the ever-expanding material architectures and applications of hollow structures in all branches of catalysis, including bio-, electro-, and photocatalysis. First, the main synthesis strategies toward hollow materials are succinctly summarized, with emphasis on the (regioselective) incorporation of various types of catalytic functionalities within their different subunits. The principles underlying the scientific and technological interest in hollow materials as solid catalysts, or catalyst carriers, are then comprehensively reviewed. Aspects covered include the stabilization of catalysts by encapsulation, the introduction of molecular sieving or stimuli-responsive "auxiliary" functionalities, as well as the single-particle, spatial compartmentalization of various catalytic functions to create multifunctional (bio)catalysts. Examples are also given on the applications which hollow structures find in the emerging fields of electro- and photocatalysis, particularly in the context of the sustainable production of chemical energy carriers. Finally, a critical perspective is provided on the plausible evolution lines for this thriving scientific field, as well as the main practical challenges relevant to the reproducible and scalable synthesis and utilization of hollow micro- and nanostructures as solid catalysts. © 2016 American Chemical Society.
    view abstract10.1021/acs.chemrev.6b00374
  • In Situ EPR Study of the Redox Properties of CuO-CeO2 Catalysts for Preferential CO Oxidation (PROX)
    Wang, F. and Büchel, R. and Savitsky, A. and Zalibera, M. and Widmann, D. and Pratsinis, S.E. and Lubitz, W. and Schüth, F.
    ACS Catalysis 6 (2016)
    Understanding the redox properties of metal oxide based catalysts is a major task in catalysis research. In situ electron paramagnetic resonance (EPR) spectroscopy is capable of monitoring the change of metal ion valences and formation of active sites during redox reactions, allowing for the identification of ongoing redox pathways. Here in situ EPR spectroscopy combined with online gas analysis, supported by ex situ X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), temporal analysis of product (TAP), and mass spectrometry (MS) studies, was utilized to study the redox behavior of CuO-CeO2 catalysts under PROX conditions (preferential oxidation of carbon monoxide in hydrogen). Two redox mechanisms are revealed: (i) a synergetic mechanism that involves the redox pair Ce4+/Ce3+ during oxidation of Cu0/Cu+ species to Cu2+ and (ii) a direct mechanism that bypasses the redox pair Ce4+/Ce3+. In addition, EPR experiments with isotopically enriched 17O2 established the synergetic mechanism as the major redox reaction pathway. The results emphasize the importance of the interactions between Cu and Ce atoms for catalyst performance. With the guidance of these results, an optimized CuO-CeO2 catalyst could be designed. A rather wide temperature operation window of 11 K (from 377 to 388 K), with 99% conversion efficiency and 99% selectivity, was achieved for the preferential oxidation of CO in a H2 feed. © 2016 American Chemical Society.
    view abstract10.1021/acscatal.6b00589
  • In Situ Hydrocracking of Fischer-Tropsch Hydrocarbons: CO-Prompted Diverging Reaction Pathways for Paraffin and α-Olefin Primary Products
    Duyckaerts, N. and Trotuş, I.-T. and Swertz, A.-C. and Schüth, F. and Prieto, G.
    ACS Catalysis 6 (2016)
    The single-step production of wax-free liquid hydrocarbons from syngas (H2 + CO) via integration of Fischer-Trospch (FT) and hydrocracking catalysts represents an attractive approach toward process intensification in compact gas-to-liquid technologies. Despite current, intensive efforts on the development of hybrid (multifunctional) catalysts to this end, not much is known about the reactivity of different FT primary products on hydrocracking catalysts under syngas. Using model compounds, the individual and collective reactivities of n-paraffin and α-olefin FT primary products were systematically studied on a Pt/nano-H-ZSM-5 hydrocracking catalyst under H2 (standard hydrocracking) and syngas (in situ hydroprocessing) atmospheres. Under H2, both reactants show indistinguishable reactivity as rapid olefin hydrogenation precedes hydrocracking. Under syngas, however, inhibition of (de)hydrogenation functionalities by CO poisoning of metal sites leads to a notable divergence of the reaction pathways for n-paraffins and α-olefins. Under these conditions, α-olefins showed enhanced reactivity, as an initial dehydrogenative activation step is not required, and contributed to moderate secondary cracking, likely via enhanced competitive adsorption on the acid sites. Besides, CO poisoning restored the intrinsic activity of the zeolite for the oligomerization of short-chain (α-)olefins, providing an additional net chain-growth pathway, which contributes to reducing the overall yield to undesired gas (C4-) hydrocarbons. These findings emphasize the key role of not only the chain-length distribution, but also the olefinic content of the FT primary hydrocarbons for the ultimate product distribution, and suggest guidelines for the design of multifunctional catalysts for the single-step synthesis of liquid hydrocarbons from syngas. © 2016 American Chemical Society.
    view abstract10.1021/acscatal.6b00904
  • Local Platinum Environments in a Solid Analogue of the Molecular Periana Catalyst
    Soorholtz, M. and Jones, L.C. and Samuelis, D. and Weidenthaler, C. and White, R.J. and Titirici, M.-M. and Cullen, D.A. and Zimmermann, T. and Antonietti, M. and Maier, J. and Palkovits, R. and Chmelka, B.F. and Schüth, F.
    ACS Catalysis 6 (2016)
    Combining advantages of homogeneous and heterogeneous catalysis by incorporating active species on a solid support is often an effective strategy for improving overall catalyst performance, although the influences of the support are generally challenging to establish, especially at a molecular level. Here, we report the local compositions, and structures of platinum species incorporated into covalent triazine framework (Pt-CTF) materials, a solid analogue of the molecular Periana catalyst, Pt(bpym)Cl2, both of which are active for the selective oxidation of methane in the presence of concentrated sulfuric acid. By using a combination of solid-state 195Pt nuclear magnetic resonance (NMR) spectroscopy, aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), important similarities and differences are observed between the Pt-CTF and Periana catalysts, which are likely related to their respective macroscopic reaction properties. In particular, wide-line solid-state 195Pt NMR spectra enable direct measurement, identification, and quantification of distinct platinum species in as-synthesized and used Pt-CTF catalysts. The results indicate that locally ordered and disordered Pt sites are present in as-synthesized Pt-CTF, with the former being similar to one of the two crystallographically distinct Pt sites in crystalline Pt(bpym)Cl2. A distribution of relatively disordered Pt moieties is also present in the used catalyst, among which are the principal active sites. Similarly XAS shows good agreement between the measured data of Pt-CTF and a theoretical model based on Pt(bpym)Cl2. Analyses of the absorption spectra of Pt-CTF used for methane oxidation suggests ligand exchange, as predicted for the molecular catalyst. XPS analyses of Pt(bpym)Cl2, Pt-CTF, as well as the unmodified ligands, further corroborate platinum coordination by pyridinic N atoms. Aberration-corrected high-angle annular dark-field STEM proves that Pt atoms are distributed within Pt-CTF before and after catalysis. The overall results establish the close similarities of Pt-CTF and the molecular Periana catalyst Pt(bpym)Cl2, along with differences that account for their respective properties. (Figure Presented). © 2016 American Chemical Society.
    view abstract10.1021/acscatal.5b02305
  • Nanocasting Design and Spatially Selective Sulfonation of Polystyrene-Based Polymer Networks as Solid Acid Catalysts
    Richter, F.H. and Sahraoui, L. and Schüth, F.
    Chemistry - A European Journal 22 (2016)
    Nanocasting is a general and widely applied method in the generation of porous materials during which a sacrificial solid template is used as a mold on the nanoscale. Ideally, the resulting structure is the inverse of the template. However, replication is not always as direct as anticipated, so the influences of the degree of pore filling and of potential restructuring processes after removal of the template need to be considered. These apparent limitations give rise to opportunities in the synthesis of poly(styrene-co-divinylbenzene) (PSD) polymer networks of widely varying porosities (BET surface area=63–562 m2g−1; Vtot=0.18–1.05 cm3g−1) by applying a single synthesis methodology. In addition, spatially selective sulfonation on the nanoscale seems possible. Together, nanocasting and sulfonation enable rational catalyst design. The highly porous nanocast and predominantly surface-sulfonated PSD networks approach the activity of the corresponding molecular catalyst, para-toluenesulfonic acid, and exceed those of commercial ion-exchange polymers in the depolymerization of macromolecular inulin. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/chem.201603069
  • Nitrogen-Doped Ordered Mesoporous Carbon Supported Bimetallic PtCo Nanoparticles for Upgrading of Biophenolics
    Wang, G.-H. and Cao, Z. and Gu, D. and Pfänder, N. and Swertz, A.-C. and Spliethoff, B. and Bongard, H.-J. and Weidenthaler, C. and Schmidt, W. and Rinaldi, R. and Schüth, F.
    Angewandte Chemie - International Edition 55 (2016)
    Hydrodeoxygenation (HDO) is an attractive route for the upgrading of bio-oils produced from lignocellulose. Current catalysts require harsh conditions to effect HDO, decreasing the process efficiency in terms of energy and carbon balance. Herein we report a novel and facile method for synthesizing bimetallic PtCo nanoparticle catalysts (ca. 1.5 nm) highly dispersed in the framework of nitrogen-doped ordered mesoporous carbon (NOMC) for this reaction. We demonstrate that NOMC with either 2D hexagonal (p6m) or 3D cubic (Im3m) structure can be easily synthesized by simply adjusting the polymerization temperature. We also demonstrate that PtCo/NOMC (metal loading: Pt 9.90 wt %; Co 3.31 wt %) is a highly effective catalyst for HDO of phenolic compounds and “real-world” biomass-derived phenolic streams. In the presence of PtCo/NOMC, full deoxygenation of phenolic compounds and a biomass-derived phenolic stream is achieved under conditions of low severity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201511558
  • Precise synthesis of discrete and dispersible carbon-protected magnetic nanoparticles for efficient magnetic resonance imaging and photothermal therapy
    Lu, A.-H. and Zhang, X.-Q. and Sun, Q. and Zhang, Y. and Song, Q. and Schüth, F. and Chen, C. and Cheng, F.
    Nano Research 9 (2016)
    Carbon-protected magnetic nanoparticles exhibit long-term stability in acid or alkaline medium, good biocompatibility, and high saturation magnetization. As a result, they hold great promise for magnetic resonance imaging, photothermal therapy, etc. However, since pyrolysis, which is often required to convert the carbon precursors to carbon, typically leads to coalescence of the nanoparticles, the obtained carbon-protected magnetic nanoparticles are usually sintered as a non-dispersible aggregation. We have successfully synthesized discrete, dispersible, and uniform carbon-protected magnetic nanoparticles via a precise surface/interface nano-engineering approach. Remarkably, the nanoparticles possess excellent water-dispersibility, biocompatibility, a high T2 relaxivity coefficient (384 mM–1·s–1), and a high photothermal heating effect. Furthermore, they can be used as multifunctional core components suited for future extended investigation in early diagnosis, detection and therapy, catalysis, separation, and magnetism. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
    view abstract10.1007/s12274-016-1042-9
  • Selective Methane Oxidation Catalyzed by Platinum Salts in Oleum at Turnover Frequencies of Large-Scale Industrial Processes
    Zimmermann, T. and Soorholtz, M. and Bilke, M. and Schüth, F.
    Journal of the American Chemical Society 138 (2016)
    Direct catalytic methane functionalization, a "dream reaction", is typically characterized by relatively low catalyst activities. This also holds for the n2-(2,2′-bipyrimidyl)dichloroplatinum(II) [(bpym)PtCl2, 1] catalyst which oxidizes methane to methyl bisulfate in sulfuric acid. Nevertheless, it is arguably still one of the best systems for the partial oxidation of methane reported so far. Detailed studies of the dependence of activity on the SO3 concentration and the interplay with the solubility of different platinum compounds revealed potassium tetrachloroplatinate (K2PtCl4) as an extremely active, selective, and stable catalyst, reaching turnover frequencies (TOFs) of more than 25,000 h-1 in 20% oleum with selectivities above 98%. The TOFs are more than 3 orders of magnitude higher compared to the original report on (bpym)PtCl2 and easily reach or exceed those realized in commercial industrial processes, such as the Cativa process for the carbonylation of methanol. Also space-time-yields are on the order of large-scale commercialized processes. © 2016 American Chemical Society.
    view abstract10.1021/jacs.6b05167
  • Structure-Activity-Stability Relationships for Space-Confined PtxNiy Nanoparticles in the Oxygen Reduction Reaction
    Mezzavilla, S. and Baldizzone, C. and Swertz, A.-C. and Hodnik, N. and Pizzutilo, E. and Polymeros, G. and Keeley, G.P. and Knossalla, J. and Heggen, M. and Mayrhofer, K.J.J. and Schüth, F.
    ACS Catalysis 6 (2016)
    This study focuses on the synthesis and electrochemical performance (i.e, activity and stability) of advanced electrocatalysts for the oxygen reduction reaction (ORR), made of Pt-Ni nanoparticles embedded in hollow graphitic spheres (HGS). The mechanism of the confined space alloying, that is, the controlled alloying of bimetallic precursors with different compositions (i.e., Pt3Ni, PtNi, and PtNi3) within the HGS mesoporous shell, was examined in detail. It was found that the presence of platinum during the reduction step, as well as the application of high annealing temperatures (at least 850°C for 3.5h in Ar), are necessary conditions to achieve the complete encapsulation and the full stability of the catalysts. The evolution of the activity, the electrochemical surface area, and the residual alloy composition of the Pt-Ni@HGS catalysts was thoroughly monitored (at the macro- and nanoscale level) under different degradation conditions. After the initial activation, the embedded Pt-Ni nanoparticles (3-4 nm in size) yield mass activities that are 2- to 3.5-fold higher than that of pure Pt@HGS (depending on the alloy composition). Most importantly, it is demonstrated that under the normal operation range of an ORR catalyst in PEM-FCs (potential excursions between 0.4 and 1.0 VRHE) both the nanoparticle-related degradation pathways (particle agglomeration) and dealloying phenomena are effectively suppressed, irrespectively of the alloy composition. Thus, the initial enhanced activity is completely maintained over an extended degradation protocol. In addition, owing to the peculiar configuration of the catalysts consisting of space-confined nanoparticles, it was possible to elucidate the impact of the dealloying process (as a function of alloy composition and severity of the degradation protocols) separately from other parallel phenomena, providing valuable insight into this elusive degradation mechanism. (Graph Presented). © 2016 American Chemical Society.
    view abstract10.1021/acscatal.6b02221
  • Synthesis of N-alkyl-4-vinylpyridinium-based cross-linked polymers and their catalytic performance for the conversion of fructose into 5-hydroxymethylfurfural
    Ruby, M.-P. and Schüth, F.
    Green Chemistry 18 (2016)
    We developed a new acid-free and metal-free heterogeneous catalytic system for the dehydration of fructose into 5-hydroxymethylfurfural (HMF). These catalysts are ionic polymers based on 4-vinylpyridine, crosslinked with divinylbenzene. The effect of different polymer properties, like the alkyl chain length at the pyridinium nitrogen, the type of anion, the porosity, the degree of post polymerization modification as well as the effect of temperature was investigated. Poly(N-alkylvinylpyridinium bromides) showed the best results. A maximum HMF yield of 77% after 0.5 h at 180 °C, using ethanol as the low boiling solvent, was achieved. Most of the byproducts are the acetals of HMF with the alcohol medium, which are often converted in downstream processes in the same manner as HMF. Thus, one can effectively consider the catalyst system as almost fully selective to HMF. © 2016 The Royal Society of Chemistry.
    view abstract10.1039/c5gc02949j
  • Zeolite Beta Formation from Clear Sols: Silicate Speciation, Particle Formation and Crystallization Monitored by Complementary Analysis Methods
    Castro, M. and Haouas, M. and Lim, I. and Bongard, H.J. and Schüth, F. and Taulelle, F. and Karlsson, G. and Alfredsson, V. and Breyneart, E. and Kirschhock, C.E.A. and Schmidt, W.
    Chemistry - A European Journal 22 (2016)
    The formation of silicate nanoaggregates (NAs) at the very early stages of precursor sols and zeolite beta crystallization from silicate nanoparticles (NPs) are investigated in detail using a combination of different analysis methods, including liquid-state29Si,27Al,14N, and1H NMR spectroscopy, mass spectrometry (MS), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy at cryogenic temperatures (cryo-TEM). Prior to hydrothermal treatment, silicate NAs are observed if the Si/OH ratio in the reaction mixture is greater than 1. Condensation of oligomers within the NAs then generates NPs. Aluminum doped into the synthesis mixtures is located exclusively in the NPs, and is found exclusively in a state that is fourfold connected to silicate, favoring their condensation and aggregation. These results are in agreement with general trends observed for other systems. Silicate NAs are essential intermediates for zeolite formation and are generated by the aggregation of hydrated oligomers, aluminate, and templating cations. Subsequent further intra-nanoaggregate silicate condensation results in the formation of NPs.1H and14N liquid NMR as well as diffusion ordered spectroscopy (DOSY) experiments provide evidence for weakly restricted rotational and translational mobility of the organic template within NAs as a consequence of specific silicate–template interactions. NAs thus appear as key species in clear sols, and their presence in the precursor sol favors silicate condensation and further crystallization, promoted either by increasing the Si/OH ratio or by heating. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/chem.201600511
  • Activation of carbon-supported catalysts by ozonized acidic solutions for the direct implementation in (electro-)chemical reactors
    Baldizzone, C. and Mezzavilla, S. and Hodnik, N. and Zeradjanin, A.R. and Kostka, A. and Schüth, F. and Mayrhofer, K.J.J.
    Chemical Communications 51 (2015)
    This work introduces a practical and scalable post-synthesis treatment for carbon-supported catalysts designed to achieve complete activation and, if necessary, simultaneously surface dealloying. The core concept behind the method is to control the potential without utilizing any electrochemical equipment, but rather by applying an appropriate gas mixture to a catalyst suspension. © 2015 The Royal Society of Chemistry.
    view abstract10.1039/c4cc08480b
  • Ammonia decomposition over iron phthalocyanine-based materials
    Tüysüz, H. and Schüth, F. and Zhi, L. and Müllen, K. and Comotti, M.
    ChemCatChem 7 (2015)
    Iron phthalocyanine-based materials have been used herein as efficient catalysts for the ammonia decomposition reaction. These materials showed high activity, even superior to that showed by the commercial nickel-based catalyst and iron-doped carbon nanotubes, which were used as benchmarks in this study. Catalyst stability under reaction conditions appeared satisfactory, because no deactivation phenomena were observed. The type of the phthalocyanine precursor did not affect the catalytic performance; however, the preparation method had a strong effect. If the resulting material was exposed to the reaction conditions, some structural modification occurred. No clear correlation between phase composition and activity could be established because similar nitrogen content and similar crystalline domains in the sample led to different behaviors. However, the results of extensive characterization suggested that catalytic activities and conversion profiles were most likely dependent on material textural properties and thus on the preparation method used. The accessibility of iron species seems to be limited for catalysts prepared under vacuum. These phenomena are most likely responsible for the activation profile and for the low catalytic activity typical of these materials. In contrast, higher accessibility of iron species, typical of materials prepared under argon, would lead to improved and stable catalytic performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cctc.201500024
  • Amphiphilic Pickering Emulsifiers Based on Mushroom-Type Janus Particles
    Passas-Lagos, E. and Schüth, F.
    Langmuir 31 (2015)
    Iron-based mushroom-type Janus particles consisting of a poly(sytrene-co-divinylbenzene) and a silica moiety both with controllable morphologies were successfully synthesized on the gram scale and investigated as surfactants for Pickering emulsions. Two oil-water model systems, namely toluene-water and vegetable oil-water, were stabilized, giving mainly water-in-oil (w/o) emulsions. By varying several parameters, including Janus particle morphologies and the oil-water ratio, fine-tuning of the emulsion systems was possible; it was even possible to invert the continuous phase to an oil-in-water (o/w) system. Furthermore, the emulsions were stable against coalescence and sedimentation and could be easily separated by centrifugation or a strong magnet. The synthesized mushroom-type Janus particles are suitable for creating Pickering emulsions and can be used as building blocks for creating nanostructures with tailored properties for specific applications. (Chemical Equation Presented). © 2015 American Chemical Society.
    view abstract10.1021/acs.langmuir.5b01198
  • Bridging the gap between insightful simplicity and successful complexity: From fundamental studies on model systems to technical catalysts
    Prieto, G. and Schüth, F.
    Journal of Catalysis 328 (2015)
    When Haldor Topsøe founded his company in 1940, the application of solid catalysts in industrial chemical processes was still in its early phase. At that time, catalyst development and optimization strongly relied on phenomenological approaches and experimental know-how, whereas little knowledge existed on the nature of the catalytically active species and how to tune their structure and concentration. For more than 70 years, Topsøe has advocated the need of "bringing more scientific understanding to the field of catalysis," becoming a prominent figure in the transition of catalyst preparation - a word with an alchemical connotation - to catalyst synthesis, based on scientific principles. Numerous fundamental studies of his team and collaborators on simplified model catalysts have added substantially to the current understanding of a significant number of industrially relevant systems in particular, and the principles of action of solid catalysts in general. This article reviews some key advancements that the Topsøe team has contributed to the field of catalyst development, rooted in fundamental studies with either 2D or 3D model materials. Examples are provided of how the acquired scientific knowledge was successfully translated into innovations in the manufacture of technical catalysts. Next to the work of the Topsøe group, a broader and updated perspective of the use of model systems to investigate fundamental aspects of catalyst development is presented. A number of selected case studies are reviewed, which we find illustrative of recent findings with implications for the design and synthesis of solid catalysts. © 2015 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.jcat.2014.12.009
  • Butadiene from acetylene-ethylene cross-metathesis
    Trotuş, I.-T. and Zimmermann, T. and Duyckaerts, N. and Geboers, J. and Schüth, F.
    Chemical Communications 51 (2015)
    Acetylene to butadiene direct synthesis, via enyne cross-metathesis, is demonstrated with commercial ruthenium carbene catalysts. Using excess of ethylene, yields greater than 50% are obtained. High activity is observed in the first minute of the reaction (TOF &gt; 800 h-1 based on butadiene). Catalyst reusability and poisoning are discussed. This journal is © The Royal Society of Chemistry 2015.
    view abstract10.1039/c5cc00853k
  • Controllable Synthesis of Mesoporous Peapod-like Co3O4@Carbon Nanotube Arrays for High-Performance Lithium-Ion Batteries
    Gu, D. and Li, W. and Wang, F. and Bongard, H. and Spliethoff, B. and Schmidt, W. and Weidenthaler, C. and Xia, Y. and Zhao, D. and Schüth, F.
    Angewandte Chemie - International Edition 54 (2015)
    Abstract Transition metal oxides are regarded as promising anode materials for lithium-ion batteries because of their high theoretical capacities compared with commercial graphite. Unfortunately, the implementation of such novel anodes is hampered by their large volume changes during the Li+ insertion and extraction process and their low electric conductivities. Herein, we report a specifically designed anode architecture to overcome such problems, that is, mesoporous peapod-like Co<inf>3</inf>O<inf>4</inf>@carbon nanotube arrays, which are constructed through a controllable nanocasting process. Co<inf>3</inf>O<inf>4</inf> nanoparticles are confined exclusively in the intratubular pores of the nanotube arrays. The pores between the nanotubes are open, and thus render the Co<inf>3</inf>O<inf>4</inf> nanoparticles accessible for effective electrolyte diffusion. Moreover, the carbon nanotubes act as a conductive network. As a result, the peapod-like Co<inf>3</inf>O<inf>4</inf>@carbon nanotube electrode shows a high specific capacity, excellent rate capacity, and very good cycling performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201501475
  • Effect of reduction–oxidation treatment on structure and catalytic properties of ordered mesoporous Cu–Mg–Al composite oxides
    Lu, J. and Zhang, Y. and Jiao, C. and Megarajan, S.K. and Gu, D. and Yang, G. and Jiang, H. and Jia, C. and Schüth, F.
    Science Bulletin 60 (2015)
    Ordered mesoporous Cu–Mg–Al composite oxides were synthesized via the one-pot evaporation-induced self-assembly strategy. Using this method, copper was first homogeneously incorporated into the ordered mesoporous spinel matrix. After H2 reduction treatment, according to X-ray diffraction (XRD) and transmission electron microscopy (TEM) results, copper existed as metallic nanoparticles with the size of 6–10 nm that well decorated the parent mesoporous skeleton. The metallic nanoparticles were then re-oxidized to copper oxide when exposed to air or during CO oxidation reaction at low temperatures. Thus, copper migrated from bulk spinel phase to the surface after the reduction–oxidation treatment. Moreover, the copper on the surface was re-incorporated into the bulk spinel phase by further thermal treatment at much higher temperature in the presence of air. The correlation between the state of copper in the mesoporous composite oxides and the catalytic performance toward CO oxidation was studied. It was found that copper existed as oxide nanoparticles on the surface of mesoporous Mg–Al skeleton is much more active than that existed as lattice Cu ions in spinel phase. © 2015, Science China Press and Springer-Verlag Berlin Heidelberg.
    view abstract10.1007/s11434-015-0805-0
  • Energy storage technologies as options to a secure energy supply
    Ausfelder, F. and Beilmann, C. and Bertau, M. and Bräuninger, S. and Heinzel, A. and Hoer, R. and Koch, W. and Mahlendorf, F. and Metzelthin, A. and Peuckert, M. and Plass, L. and Räuchle, K. and Reuter, M. and Schaub, G. and Schiebahn, S. and Schwab, E. and Schüth, F. and Stolten, D. and Teßmer, G. and Wagemann, K. and Ziegahn, K.-F.
    Chemie-Ingenieur-Technik 87 (2015)
    The current energy system is subject to a profound change: A system, designed to cater to energy needs by supplying fossil fuels is now expected to shift to integrate ever larger amounts of renewable energies to achieve overall a more sustainable energy supply. The challenges arising from this paradigm change are currently most obvious in the area of electric power supply. However, it affects the entire energy system, albeit with different effects. Within the energy system, various independent grids fulfill the function to transport and distribute energy or energy carriers in order to address spatially different energy supply and demand situations. Temporal variations are currently addressed by just-in-time production of the required energy form. However, renewable energy sources generally supply their energy independently from any specific energy demand. Their contribution to the overall energy system is expected to increase significantly. Energy storage technologies also represent an option to compensate for a temporal difference in energy supply and demand. Energy storage systems have the ability for a controlled take-up of a certain amount of energy, storing this energy within a storage media on a relevant timescale and a controlled redispatch of the energy after a certain time delay. Energy storage systems can also be constructed as process chains by combinations of unit operations, each covering different aspects of those functions. Large-scale mechanical storage options for electrical power are currently almost exclusively pumped hydro storage. These systems might be complemented in the future by compressed-air storage and maybe liquid-air facilities. There are several electrochemical storage technologies currently under investigation for their suitability as large scale electrical energy storage in various stages of research, development, and demonstration. Thermal energy storage technologies are based on a large variety of storage principles: Sensible heat, latent heat (based on phase transitions), adsorption/desorption processes or on chemical reactions. The latter can be a route to permanent and loss-free storage of heat. Chemical energy storage systems are based on the energy contained within the chemical bonds of the respective storage molecules. These storage molecules can act as energy carriers. Equally well, these compounds can enter various industrial value chains in energy-intensive industrial sectors and are therefore in direct economic competition with established (fossil) supply routes for these compounds. Water electrolysis, producing hydrogen and oxygen, is and will be the key technology for the foreseeable future. Hydrogen can be transformed by various processes to other energy carriers of interest. These transformations make the stored energy accessible by different sectors of the energy system and/or as raw materials for energy-intensive industrial processes. Some functions of energy storage systems can be taken over by industrial processes. Within the overall energy system, chemical energy storage technologies open up opportunities to link, connect and interweave the various energy streams and sectors. While chemical energy storage offers a route for a stronger integration of renewable energy outside the power sector, it also creates new opportunities for increased flexibility, novel synergies and additional optimization. Several examples of specific energy utilization are discussed and evaluated with respect to energy storage applications. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstract10.1002/cite.201400183
  • Erratum: Direct observation and analysis of yolk-shell materials using low-voltage high-resolution scanning electron microscopy: Nanometal-particles encapsulated in metal-oxide, carbon, and polymer (APL Materials (2014) 2 (113317))
    Asahina, S. and Suga, M. and Takahashi, H. and Jeong, H.Y. and Galeano, C. and Schüth, F. and Terasaki, O.
    APL Materials 3 (2015)
    view abstract10.1063/1.4906321
  • General Method for the Synthesis of Hollow Mesoporous Carbon Spheres with Tunable Textural Properties
    Mezzavilla, S. and Baldizzone, C. and Mayrhofer, K.J.J. and Schüth, F.
    ACS Applied Materials and Interfaces 7 (2015)
    A versatile synthetic procedure to prepare hollow mesoporous carbon spheres (HMCS) is presented here. This approach is based on the deposition of a homogeneous hybrid polymer/silica composite shell on the outer surface of silica spheres through the surfactant-assisted simultaneous polycondensation of silica and polymer precursors in a colloidal suspension. Such composite materials can be further processed to give hollow mesoporous carbon spheres. The flexibility of this method allows for independent control of the morphological (i.e., core diameter and shell thickness) and textural features of the carbon spheres. In particular, it is demonstrated that the size of the pores within the mesoporous shell can be precisely tailored over an extended range (2-20 nm) by simply adjusting the reaction conditions. In a similar fashion, also the specific carbon surface area as well as the total shell porosity can be tuned. Most importantly, the textural features can be adjusted without affecting the dimension or the morphology of the spheres. The possibility to directly modify the shell textural properties by varying the synthetic parameters in a scalable process represents a distinct asset over the multistep hard-templating (nanocasting) routes. As an exemplary application, Pt nanoparticles were encapsulated in the mesoporous shell of HMCS. The resulting Pt@HMCS catalyst showed an enhanced stability during the oxygen reduction reaction, one of the most important reactions in electrocatalysis. This new synthetic procedure could allow the expansion, perhaps even beyond the lab-scale, of advanced carbon nanostructured supports for applications in catalysis. © 2015 American Chemical Society.
    view abstract10.1021/acsami.5b02580
  • Highly Ordered Mesoporous Cobalt-Containing Oxides: Structure, Catalytic Properties, and Active Sites in Oxidation of Carbon Monoxide
    Gu, D. and Jia, C.-J. and Weidenthaler, C. and Bongard, H.-J. and Spliethoff, B. and Schmidt, W. and Schüth, F.
    Journal of the American Chemical Society 137 (2015)
    Co<inf>3</inf>O<inf>4</inf> with a spinel structure is a very active oxide catalyst for the oxidation of CO. In such catalysts, octahedrally coordinated Co3+ is considered to be the active site, while tetrahedrally coordinated Co2+ is assumed to be basically inactive. In this study, a highly ordered mesoporous CoO has been prepared by H<inf>2</inf> reduction of nanocast Co<inf>3</inf>O<inf>4</inf> at low temperature (250 °C). The as-prepared CoO material, which has a rock-salt structure with a single Co2+ octahedrally coordinated by lattice oxygen in Fm3¯m symmetry, exhibited unexpectedly high activity for CO oxidation. Careful investigation of the catalytic behavior of mesoporous CoO catalyst led to the conclusion that the oxidation of surface Co2+ to Co3+ causes the high activity. Other mesoporous spinels (CuCo<inf>2</inf>O<inf>4</inf>, CoCr<inf>2</inf>O<inf>4</inf>, and CoFe<inf>2</inf>O<inf>4</inf>) with different Co species substituted with non/low-active metal ions were also synthesized to investigate the catalytically active site of cobalt-based catalysts. The results show that not only is the octahedrally coordinated Co3+ highly active but also the octahedrally coordinated Co2+ species in CoFe<inf>2</inf>O<inf>4</inf> with an inverse spinel structure shows some activity. These results suggest that the octahedrally coordinated Co2+ species is easily oxidized and shows high catalytic activity for CO oxidation. © 2015 American Chemical Society.
    view abstract10.1021/jacs.5b06336
  • Insights into the molecular assembly of zeolitic imidazolate frameworks by ESI-MS
    Lim, I.H. and Schrader, W. and Schüth, F.
    Chemistry of Materials 27 (2015)
    ZIFs are an interesting class of MOFs with zeolite-like topologies, owing to their structural similarities. Rational design and synthesis of ZIFs are highly challenging due to limited understanding of their formation process from solution, as previous studies were largely on crystal growth and properties. In this contribution, we describe a systematic approach to synthesize well-defined ZIF-8 crystals at different rates of nucleation by adjusting zinc to 2-methylimidazole ratios. For the first time, we report discrete chemical species detected in ZIF-8 synthesis and trace their transition with time using ESI-MS. Cravillon et al. have previously described three essential steps in ZIF-8 nucleation: (i) complex formation, (ii) complex deprotonation, and (iii) ligand exchange and oligomerization. In our work, we were able to identify species undergoing the various steps and correlate their evolution to the different nucleation rates. Applying ESI-MS in both positive and negative modes, we identified two species, "[Zn<inf>4</inf>(C<inf>4</inf>N<inf>2</inf>H<inf>5</inf>)<inf>4</inf>(C<inf>4</inf>N<inf>2</inf>H<inf>6</inf>)<inf>2</inf>(NO<inf>3</inf>)<inf>3</inf>]+" and "[Zn<inf>4</inf>(C<inf>4</inf>N<inf>2</inf>H<inf>5</inf>)<inf>5</inf>(C<inf>4</inf>N<inf>2</inf>H<inf>6</inf>)<inf>5</inf>(NO<inf>3</inf>)<inf>4</inf>(CH<inf>3</inf>OH)]-", with changes in intensities corresponding to onset of nucleation processes. These species could potentially form the four-membered ring which is a basic structural unit in the sodalite framework. The usefulness of ESI-MS in studying ZIF formation is further demonstrated by the successful application of this technique to probe ZIF-67 syntheses. © 2015 American Chemical Society.
    view abstract10.1021/acs.chemmater.5b00614
  • MAXNET Energy - Focusing Research in Chemical Energy Conversion on the Electrocatlytic Oxygen Evolution
    Auer, A.A. and Cap, S. and Antonietti, M. and Cherevko, S. and Deng, X. and Papakonstantinou, G. and Sundmacher, K. and Brüller, S. and Antonyshyn, I. and Dimitratos, N. and Davis, R.J. and Böhm, K.-H. and Fechler, N. and Freakley, S. and Grin, Y. and Gunnoe, B.T. and Haj-Hariri, H. and Hutchings, G. and Liang, H. and Mayrhofer, K.J.J. and Müllen, K. and Neese, F. and Ranjan, C. and Sankar, M. and Schlögl, R. and Schüth, F. and Spanos, I. and Stratmann, M. and Tüysüz, H. and Vidakovic-Koch, T. and Yi, Y. and Zangari, G.
    Green 5 (2015)
    MAXNET Energy is an initiative of the Max Planck society in which eight Max Planck institutes and two external partner institutions form a research consortium aiming at a deeper understanding of the electrocatalytic conversion of small molecules. We give an overview of the activities within the MAXNET Energy research consortium. The main focus of research is the electrocatalytic water splitting reaction with an emphasis on the anodic oxygen evolution reaction (OER). Activities span a broad range from creation of novel catalysts by means of chemical or material synthesis, characterization and analysis applying innovative electrochemical techniques, atomistic simulations of state-of-the-art x-ray spectroscopy up to model-based systems analysis of coupled reaction and transport mechanisms. Synergy between the partners in the consortium is generated by two modes of cooperation - one in which instrumentation, techniques and expertise are shared, and one in which common standard materials and test protocols are used jointly for optimal comparability of results and to direct further development. We outline the special structure of the research consortium, give an overview of its members and their expertise and review recent scientific achievements in materials science as well as chemical and physical analysis and techniques. Due to the extreme conditions a catalyst has to endure in the OER, a central requirement for a good oxygen evolution catalyst is not only its activity, but even more so its high stability. Hence, besides detailed degradation studies, a central feature of MAXNET Energy is a standardized test setup/protocol for catalyst stability, which we propose in this contribution. ©2015 by De Gruyter Mouton.
    view abstract10.1515/green-2015-0021
  • Mechanocatalytic depolymerization of lignocellulose performed on hectogram and kilogram scales
    Kaufman Rechulski, M.D. and Käldström, M. and Richter, U. and Schüth, F. and Rinaldi, R.
    Industrial and Engineering Chemistry Research 54 (2015)
    Mechanocatalytic depolymerization of lignocellulose constitutes a new frontier in biorefining. In a one-pot process, the combination of mechanical forces and acid catalysis leads to the full conversion of (dried) lignocellulose into water-soluble products (oligosaccharides and lignin fragments). In solution, these products undergo hydrolysis and other reactions, rendering high yields of monosaccharides along with precipitation of a sulfur-free lignin. Therefore, the water-soluble oligosaccharides may serve as a unique replacement for glucose and xylose for the production of platform chemicals. In this work, we report the results obtained from mechanocatalytic depolymerization of α-cellulose, beechwood, and poplar wood performed in Simoloyer mills operating on hectogram and kilogram scales. Irrespective of the process scale, full conversion of the substrate into "water-soluble (ligno)celluloses", within milling durations of 1-3 h, is achieved. A phenomenological analysis of parameters for the process upscaling is provided. Moreover, the energy consumption of the process on different scales is assessed. Remarkably, energy consumption significantly decreases (from ca. 200 MWh·t-1 to 9.6 MWh·t-1) with upscaling of the experiment from 1 g (planetary mill) to 1 kg. This increase in energy efficiency constitutes key evidence for the feasibility of the mechanocatalytic depolymerization on a large scale. © 2015 American Chemical Society.
    view abstract10.1021/acs.iecr.5b00224
  • Mesoporous Sulfonated Carbon Materials Prepared by Spray Pyrolysis
    Duyckaerts, N. and Trotuş, I.-T. and Nese, V. and Swertz, A.-C. and Auris, S. and Wiggers, H. and Schüth, F.
    ChemCatChem 7 (2015)
    A one-step approach was developed for the production of mesoporous sulfonated carbon materials by means of an aerosol synthesis. Nebulizing a clear aqueous solution of sucrose and sulfuric acid through a heated oven leads to subsequent dehydration, carbonization and sulfonation of the carbohydrate structure, in less than two seconds residence time. Acid site concentrations ranging from 0.1 to 0.6 mmol g-1 can be obtained. Porosity can easily be introduced via salt templating, and can be adjusted by varying the loading and type of salt used. The highest surface area was obtained with Li<inf>2</inf>SO<inf>4</inf>, giving a BET surface area of 506 m2 g-1 and a mesopore size distribution between 2 and 8 nm. Fructose dehydration and inulin hydrolysis showed that the porous materials synthesized by salt templating are more active than the bulk ones, especially for inulin hydrolysis, for which the initial activity is enhanced by a factor of seven, making these materials competitive with the most active commercial resins. A one-step synthesis for the production of mesoporous sulfonated carbon materials is presented, by which sulfuric acid and an organic precursor are converted, in one step, to an active sulfonated carbon material containing high surface area. Fructose dehydration and inulin hydrolysis reveal the competitiveness with commercial acidic resins. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cctc.201500483
  • Pseudomorphic Generation of Supported Catalysts for Glycerol Oxidation
    Deng, X. and Dodekatos, G. and Pupovac, K. and Weidenthaler, C. and Schmidt, W. and Schüth, F. and Tüysüz, H.
    ChemCatChem 7 (2015)
    A catalyst consisting of copper nanoparticles (15-20 nm in size) supported on ordered mesoporous cobalt monoxide was synthesized by the one-step reduction of ethanol from nanocast copper cobalt spinel oxides. The small-angle X-ray scattering patterns showed that the ordered mesostructure was maintained after post-treatment, and the cross-section scanning electron microscopy images showed that the Cu nanoparticles were distributed homogeneously throughout the mesoporous CoO framework. The materials were tested as noble-metal-free catalysts for the oxidation of glycerol under alkaline conditions. The catalytic data showed that the presence of Cu nanoparticles greatly enhanced the catalytic performance. Nothing noble: A catalyst consisting of copper nanoparticles (NPs, 15-20 nm in size) supported on ordered mesoporous cobalt monoxide is synthesized by the one-step reduction with ethanol from nanocast copper cobalt spinel oxides. As a noble-metal-free catalyst for the oxidation of glycerol, the presence of Cu NPs greatly enhances the catalytic performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cctc.201500703
  • The Yin and Yang in the development of catalytic processes: Catalysis research and reaction engineering
    Prieto, G. and Schüth, F.
    Angewandte Chemie - International Edition 54 (2015)
    A synergetic interplay: Catalysis is a key research field within BASF. Successful industrial chemistry is always the result of a combination of catalyst and process development. The interplay of catalyst chemistry and reaction engineering is discussed for processes such as the sulfuric acid production, ammonia synthesis, methanol synthesis, fluid catalytic cracking, and direct epoxidation of propylene. (Figure Presented). © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstract10.1002/anie.201409885
  • Uniform 2 nm gold nanoparticles supported on iron oxides as active catalysts for CO oxidation reaction: Structure-activity relationship
    Guo, Y. and Gu, D. and Jin, Z. and Du, P.-P. and Si, R. and Tao, J. and Xu, W.-Q. and Huang, Y.-Y. and Senanayake, S. and Song, Q.-S. and Jia, C.-J. and Schüth, F.
    Nanoscale 7 (2015)
    Uniform Au nanoparticles (∼2 nm) with narrow size-distribution (standard deviation: 0.5-0.6 nm) supported on both hydroxylated (Fe-OH) and dehydrated iron oxide (Fe-O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) showed high homogeneity in the supported Au nanoparticles. The ex situ and in situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reduction by hydrogen (H<inf>2</inf>-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe-OH < Au/Fe-O) and CD (Au/Fe-OH > Au/Fe-O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe-OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeO<inf>x</inf> catalysts with very similar structural characteristics in CO oxidation. © The Royal Society of Chemistry 2015.
    view abstract10.1039/c4nr06967f
  • A polyphenylene support for pd catalysts with exceptional catalytic activity
    Wang, F. and Mielby, J. and Richter, F.H. and Wang, G. and Prieto, G. and Kasama, T. and Weidenthaler, C. and Bongard, H.-J. and Kegnæs, S. and Fürstner, A. and Schüth, F.
    Angewandte Chemie - International Edition 53 (2014)
    We describe a solid polyphenylene support that serves as an excellent platform for metal-catalyzed reactions that are normally carried out under homogeneous conditions. The catalyst is synthesized by palladium-catalyzed Suzuki coupling which directly results in formation of palladium nanoparticles confined to a porous polyphenylene network. The composite solid is in turn highly active for further Suzuki coupling reactions, including non-activated substrates that are challenging even for molecular catalysts. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201404912
  • Carbon-based yolk-shell materials for fuel cell applications
    Galeano, C. and Baldizzone, C. and Bongard, H. and Spliethoff, B. and Weidenthaler, C. and Meier, J.C. and Mayrhofer, K.J.J. and Schüth, F.
    Advanced Functional Materials 24 (2014)
    The synthesis of yolk-shell catalysts, consisting of platinum or gold-platinum cores and graphitic carbon shells, and their electrocatalytic stabilities are described. Different encapsulation pathways for the metal nanoparticles are explored and optimized. Electrochemical studies of the optimized AuPt, @C catalyst revealed a high stability of the encapsulated metal particles. However, in order to reach full activity, several thousand potential cycles are required. After the electrochemical surface area is fully developed, the catalysts show exceptionally high stability, with almost no degradation over approximately 30 000 potential cycles between 0.4 and 1.4 VRHE. Encapsulation of noble metals in graphitic hollow shells by hard templating is explored as a means for stabilizing fuel cell catalysts. Small platinum particles can be encapsulated, but the achievable loading is too small. Encapsulation of Au-Pt yolk-shell particles allows higher loading, and with such cores, stable catalysts could be produced. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/adfm.201302239
  • Catalytic reactions of acetylene: A feedstock for the chemical industry revisited
    Trotuş, I.-T. and Zimmermann, T. and Schüth, F.
    Chemical Reviews 114 (2014)
    An overview about the production and especially the handling of acetylene as well as the different reactions acetylene can undergo is studied. The high energy needed for its production makes acetylene much more expensive than olefins, although acetylene-based routes often require fewer production steps and show high overall product selectivity. The calcium carbide process produces acetylene as the only hydrocarbon and uses exclusively coal as a carbon source. The materials used for reactors and other equipment in contact with gaseous acetylene should be either steel that does not contain any alloy components except carbon or highly alloyed stainless steel. The use of pressurized acetylene in an advanced setup requires a compressor, as the available equipment allows just releasing acetylene with a relative pressure of 1.5 bar from the gas bottle. Base-catalyzed reactions of acetylene are more frequently encountered, since the protons of acetylene are relatively acidic for a hydrocarbon and thus, the molecule can be activated by bases.
    view abstract10.1021/cr400357r
  • Confined-space alloying of nanoparticles for the synthesis of efficient PtNi fuel-cell catalysts
    Baldizzone, C. and Mezzavilla, S. and Carvalho, H.W.P. and Meier, J.C. and Schuppert, A.K. and Heggen, M. and Galeano, C. and Grunwaldt, J.-D. and Schüth, F. and Mayrhofer, K.J.J.
    Angewandte Chemie - International Edition 53 (2014)
    The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, that is, its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen reduction reaction associated with nanoscale Pt alloys, and the excellent durability of an advanced nano-structured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0 AmgPt -1. Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined space alloying of the nanoparticles in a controlled manner in the pores of the support. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201406812
  • Control of solid catalysts down to the atomic scale: Where is the limit?
    Schüth, F.
    Angewandte Chemie - International Edition 53 (2014)
    Down to the last detail: Nanostructured solid catalysts were already known in the early 20th century, but their exact structure was unclear. Nowadays, the arrangement of atoms and particles in solids can be manipulated and analyzed down to the atomic scale (see image). The use of specific highly active catalysts enables industrially relevant reactions to be performed at room temperature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201402251
  • Deciphering 'water-soluble lignocellulose' obtained by mechanocatalysis: New insights into the chemical processes leading to deep depolymerization
    Käldström, M. and Meine, N. and Farès, C. and Schüth, F. and Rinaldi, R.
    Green Chemistry 16 (2014)
    Recently, the mechanocatalytic depolymerization of lignocelluloses yielding 'water-soluble lignocelluloses' was demonstrated. Water-soluble C5 & C6 sugars and sulfur-free lignins are formed through the saccharification of the oligosaccharides, allowing for the fractionation of biomass by simple filtration. Herein, we present an in-depth analysis of water-soluble products obtained from beechwood. The complex nature of the 'water-soluble beechwood' is investigated by 2D HSQC NMR, HPLC and gel filtration chromatography. The detailed analysis of the 'water-soluble beechwood' lends significant insights into the chemical nature of the lignocellulose depolymerization driven by the mechanical forces. This journal is © the Partner Organisations 2014.
    view abstract10.1039/c4gc00004h
  • Design criteria for stable Pt/C fuel cell catalysts
    Meier, J.C. and Galeano, C. and Katsounaros, I. and Witte, J. and Bongard, H.J. and Topalov, A.A. and Baldizzone, C. and Mezzavilla, S. and Schüth, F. and Mayrhofer, K.J.J.
    Beilstein Journal of Nanotechnology 5 (2014)
    Platinum and Pt alloy nanoparticles supported on carbon are the state of the art electrocatalysts in proton exchange membrane fuel cells. To develop a better understanding on how material design can influence the degradation processes on the nanoscale, three specific Pt/C catalysts with different structural characteristics were investigated in depth: a conventional Pt/Vulcan catalyst with a particle size of 3-4 nm and two Pt@HGS catalysts with different particle size, 1-2 nm and 3-4 nm. Specifically, Pt@HGS corresponds to platinum nanoparticles incorporated and confined within the pore structure of the nanostructured carbon support, i.e., hollow graphitic spheres (HGS). All three materials are characterized by the same platinum loading, so that the differences in their performance can be correlated to the structural characteristics of each material. The comparison of the activity and stability behavior of the three catalysts, as obtained from thin film rotating disk electrode measurements and identical location electron microscopy, is also extended to commercial materials and used as a basis for a discussion of general fuel cell catalyst design principles. Namely, the effects of particle size, inter-particle distance, certain support characteristics and thermal treatment on the catalyst performance and in particular the catalyst stability are evaluated. Based on our results, a set of design criteria for more stable and active Pt/C and Pt-alloy/C materials is suggested.& copy 2014 Meier et al.
    view abstract10.3762/bjnano.5.5
  • Direct observation and analysis of york-shell materials using low-voltage high-resolution scanning electron microscopy: Nanometal-particles encapsulated in metal-oxide, carbon, and polymer
    Asahina, S. and Suga, M. and Takahashi, H. and Young Jeong, H. and Galeano, C. and Schüth, F. and Terasaki, O.
    APL Materials 2 (2014)
    Nanometal particles show characteristic features in chemical and physical properties depending on their sizes and shapes. For keeping and further enhancing their features, the particles should be protected from coalescence or degradation. One approach is to encapsulate the nanometal particles inside pores with chemically inert or functional materials, such as carbon, polymer, and metal oxides, which contain mesopores to allow permeation of only chemicals not the nanometal particles. Recently developed low-voltage high-resolution scanning electron microscopy was applied to the study of structural, chemical, and electron state of both nanometal particles and encapsulating materials in york-shell materials of Au@C, Ru/Pt@C, Au@TiO2, and Pt@Polymer. Progresses in the following categories were shown for the york-shell materials: (i) resolution of topographic image contrast by secondary electrons, of atomic-number contrast by back-scattered electrons, and of elemental mapping by X-ray energy dispersive spectroscopy; (ii) sample preparation for observing internal structures; and (iii) X-ray spectroscopy such as soft X-ray emission spectroscopy. Transmission electron microscopy was also used for characterization of Au@C. © 2014 Author(s).
    view abstract10.1063/1.4902435
  • Encapsulation strategies in energy conversion materials
    Schüth, F.
    Chemistry of Materials 26 (2014)
    Many energy conversion materials show increased performance, if the materials are used in nanostructured form. However, this could be detrimental for stability of the materials, since during cycling the nanostructuring tends to be lost because of particle growth. This problem may be solved by encapsulation of the active material in different types of matrices or coatings, which beyond the stabilization may also provide additional functionality, such as conductivity or mechanical reinforcement. This Perspective covers the general features of encapsulation strategies, and desribes selected examples for different types of energy conversion materials. At the end, promising development lines will be discussed, together with the need for a more systematic study of the effects of encapsulation. © 2013 American Chemical Society.
    view abstract10.1021/cm402791v
  • Energy Carriers Made from Hydrogen
    Djinović, P. and Schüth, F.
    Electrochemical Energy Storage for Renewable Sources and Grid Balancing (2014)
    The increasing demand for energy and limited reserves of fossil resources as well as climate change will in the near future require the transition from fossil to renewable feedstocks for sustainable production of fuels. In the following text several well-established and also emerging technologies for hydrogen production and its integration into energy-rich carrier molecules, such as methane, methanol, oxygenates, and synthetic petroleum fuel are presented and discussed. Several important factors like the possibility of large-scale production, compatibility with existing distribution and storage infrastructure, efficient energy extraction on demand, and last but not least, tolerable impact on the environment will play key roles. Each of the fuels has its own characteristics, and thus there may not be one single solution, but the coexistence of different fuels, depending on regional boundary conditions. © 2015 Elsevier B.V. All rights reserved.
    view abstract10.1016/B978-0-444-62616-5.00012-7
  • Erratum: Deciphering 'water-soluble lignocellulose' obtained by mechanocatalysis: New insights into the chemical processes leading to deep depolymerization (Green Chemistry (2014) 16 (3528-3538))
    Käldström, M. and Meine, N. and Farès, C. and Schüth, F. and Rinaldi, R.
    Green Chemistry 16 (2014)
    view abstract10.1039/c4gc90048k
  • Fractionation of 'water-soluble lignocellulose' into C5/C 6 sugars and sulfur-free lignins
    Käldström, M. and Meine, N. and Farès, C. and Rinaldi, R. and Schüth, F.
    Green Chemistry 16 (2014)
    Recently, we demonstrated the mechanocatalytic depolymerization of lignocellulosic substrates as a powerful methodology that fully converts lignocellulosic substrates into 'water-soluble lignocellulose'. We now show that the saccharification of the aqueous solution of depolymerized beechwood, pinewood and sugarcane bagasse (at 140 °C for 1 h) produces a high yield of sugars (e.g. 88-92% glucose, 3.5-8% glucose dimers and 93-98% xylose relative to the glucan and xylan fractions, respectively) and leads to precipitation of sulfur-free lignins. Noteworthy, the formation of furfurals is suppressed because the 'water-soluble lignocelluloses' undergo hydrolysis at relatively low temperatures. At 140 °C, 5-hydroxymethylfurfural and furfural are formed in yields not exceeding 1.4 and 5.7%, respectively. The separation of the carbohydrate fraction (as C5 and C6 sugars) from the lignin fraction is thus feasible by simple filtration. © the Partner Organisations 2014.
    view abstract10.1039/c4gc00168k
  • Germany's Energiewende pushes for renewables
    Saini, A. and Brick, S. and Schüth, F.
    MRS Bulletin 39 (2014)
    The Energiewende (energy transformation) is Germany's plan to move away from nuclear power and fossil fuels. Prime among the problems associated with grid-scale renewables is intermittent supply, neither wind nor solar can provide constant power. A multimillion-Euro research funding scheme provided by the Energiewende has supported materials research in Germany, including into batteries. The electronics company, Bosch, has started work on high-energy traction batteries for electric vehicles. In 2014, the French cabling company, Nexans, installed a kilometer long underground superconducting cable between two large transformers in the German city of Essen. Capable of carrying five times as much power as a normal copper cable, this type of cable also reduces transmission losses to almost zero. German Chancellor Angela Merkel has backed plans to replace existing AC transmission lines with high-voltage direct current (HVDC) lines between the north and south. One area for improvement is in wind turbine towers, which are becoming proportionally taller to capture the better wind speeds higher above the ground.
    view abstract10.1557/mrs.2014.201
  • Highly microporous monodisperse silica spheres synthesized by the Stöber process
    Bazuła, P.A. and Arnal, P.M. and Galeano, C. and Zibrowius, B. and Schmidt, W. and Schüth, F.
    Microporous and Mesoporous Materials 200 (2014)
    Silica spheres that are prepared by the Stöber process are usually considered non-porous. Here we report on a slightly modified synthesis protocol that allows preparation of microporous Stöber particles. Successive treatment with water and alcohol at room temperature results in substantial reorganization of the silica within the Stöber particles. Hydrolysis of alkoxy groups as well as condensation and re-esterification of silanol groups upon re-immersion in alcohol are crucial for that process. As the result of the silica reorganization, micropore channels are formed within the particles. After a final washing with water to remove all alkoxy groups from the particles, pure microporous silica spheres are obtained. The total pore volumes of these materials are comparable to those of zeolitic materials. © 2014 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.micromeso.2014.07.051
  • Mechanocatalytic depolymerization of cellulose and raw biomass and downstream processing of the products
    Schüth, F. and Rinaldi, R. and Meine, N. and Käldström, M. and Hilgert, J. and Rechulski, M.D.K.
    Catalysis Today 234 (2014)
    The utilization of lignocelluloses (e.g. wood, grass, crops residues and several others) shows great potential as part of the solution for decreasing the dependence of modern societies on fossil resources. In spite of this, the catalytic conversion of these renewable carbon resources via chemical and biotechnological processes is hindered by their complex polymeric nature. For this reason, chemical or enzymatic processes for hydrolysis of cellulose suffer from low efficacy due to harsh reaction conditions and high byproduct formation in case of the chemical methods, or high costs and long reaction times for the enzymatic methods. There is thus an urgent need for processes able to convert the whole plant biomass, which allow the formation of fermentable sugars and technical sulfur-free lignins. Recently, we demonstrated the combination of acid-catalysis with mechanical forces to be an efficient approach to fully overcome the recalcitrance of lignocellulose. As a result, the solvent-free depolymerization of lignocellulose (in solid-state) forms 'water-soluble lignocellulose' in quantitative yield. In this article, we present an overview of the mechanocatalytic depolymerization of lignocellulose and downstream processing of the 'water-soluble' lignocellulose' to sugar alcohols and furfurals. The water-soluble products appear to be the ideal platform at the beginning of advanced value chains of biorefining, starting with 'real' lignocellulosic substrates. © 2014 Elsevier B.V.
    view abstract10.1016/j.cattod.2014.02.019
  • Nitrogen-doped hollow carbon spheres as a support for platinum-based electrocatalysts
    Galeano, C. and Meier, J.C. and Soorholtz, M. and Bongard, H. and Baldizzone, C. and Mayrhofer, K.J.J. and Schüth, F.
    ACS Catalysis 4 (2014)
    Platinum and platinum alloys supported on carbon materials are the state of the art electrocatalysts for the essential oxygen reduction reaction (ORR) in low-temperature fuel cells. The limited stability of such materials under the often detrimental operation conditions of fuel cells still remains a critical issue to improve. In this work, we explore the impact of nitrogen-doped carbon supports on the activity and stability of platinum-based fuel cell catalysts. We present a nitrogen-doped mesostructured carbon material, nitrogen-doped hollow carbon spheres (NHCS), as a support for platinum-based electrocatalysts. A detailed study of the electrochemical activity and stability was carried out for two Pt@NHCS materials i.e., as-made material (Pt@NHCS) with a Pt particle size smaller than 2 nm and the corresponding material after thermal treatment at 850 °C (Pt@NHCST) with a Pt particle size of ca. 2-3 nm. Activity in the ORR was studied by rotating disc electrode (RDE) thin-film measurements, and electrocatalyst stability was evaluated by accelerated aging tests under simulated start-stop conditions. The performance of the NHCS-based materials was compared to the two corresponding nitrogen-free materials as well as to a standard Pt/Vulcan catalyst. The underlying degradation mechanisms of Pt@NHCS materials were investigated via identical location electron microscopy. Our results conclusively show that nitrogen doping of the carbon supports can offer benefits for achieving high initial mass activities due to improved high platinum dispersion; however, it was not found to necessarily lead to an improvement of the catalyst stability. © 2014 American Chemical Society.
    view abstract10.1021/cs5003492
  • Ordered mesoporous Cu-Ce-O catalysts for CO preferential oxidation in H2-rich gases: Influence of copper content and pretreatment conditions
    Gu, D. and Jia, C.-J. and Bongard, H. and Spliethoff, B. and Weidenthaler, C. and Schmidt, W. and Schüth, F.
    Applied Catalysis B: Environmental 152-153 (2014)
    Highly ordered mesoporous Cu-Ce-O catalysts with different Cu contents have been synthesized by using ordered mesoporous silica KIT-6 as a hard template. The mesostructural order of the negative replica is influenced by the ratio of Cu to Ce. Using XRD, HR-SEM, TEM and EDX analysis, it was found that the ordered mesostructures of the nanocomposites degenerate with increasing Cu concentration, due to CuO leaching during the template removal process and a phase separation at high Cu concentration. Cu ions can replace Ce-ion in the structure of CeO2 at Cu concentrations below 40mol%. However, the Cu concentration in the final materials is lower than expected from the ratio used in the synthesis. The activity in preferential oxidation of CO in H2-rich gases (PROX) was tested at a space velocity of 60,000mLh-1gcat -1. The activity of the mesoporous catalysts increases with the concentration of Cu and becomes stable for Cu concentrations higher than 20mol%. A CO conversion around 100 % can be attained with Cu0.20Ce0.80O2 as catalyst at 160°C. The exit CO concentration can be as low as 70ppm under these conditions. The CO2 selectivity can reach 100 % at low temperature (60- 80°C). Direct loading of CuO on the surface of mesoporous CeO2 leads to large CuO crystals and correspondingly low activity. The influence of the pretreatment atmosphere on activity was also studied. Oxidation-reduction-reoxidation cycling can improve the catalytic activity of the catalysts. © 2014 Elsevier B.V.
    view abstract10.1016/j.apcatb.2014.01.011
  • Platinum-cobalt bimetallic nanoparticles in hollow carbon nanospheres for hydrogenolysis of 5-hydroxymethylfurfural
    Wang, G.-H. and Hilgert, J. and Richter, F.H. and Wang, F. and Bongard, H.-J. and Spliethoff, B. and Weidenthaler, C. and Schüth, F.
    Nature Materials 13 (2014)
    The synthesis of 2,5-dimethylfuran (DMF) from 5-hydroxymethylfurfural (HMF) is a highly attractive route to a renewable fuel. However, achieving high yields in this reaction is a substantial challenge. Here it is described how PtCo bimetallic nanoparticles with diameters of 3.6 ± 0.7 nm can solve this problem. Over PtCo catalysts the conversion of HMF was 100% within 10 min and the yield to DMF reached 98% after 2 h, which substantially exceeds the best results reported in the literature. Moreover, the synthetic method can be generalized to other bimetallic nanoparticles encapsulated in hollow carbon spheres. © 2014 Macmillan Publishers Limited.
    view abstract10.1038/nmat3872
  • Reactivity of metal catalysts in glucose-fructose conversion
    Loerbroks, C. and vanRijn, J. and Ruby, M.-P. and Tong, Q. and Schüth, F. and Thiel, W.
    Chemistry - A European Journal 20 (2014)
    A joint experimental and computational study on the glucose-fructose conversion in water is reported. The reactivity of different metal catalysts (CrCl3, AlCl3, CuCl2, FeCl3, and MgCl2) was analyzed. Experimentally, CrCl3 and AlCl3 achieved the best glucose conversion rates, CuCl2 and FeCl3 were only mediocre catalysts, and MgCl2 was inactive. To explain these differences in reactivity, DFT calculations were performed for various metal complexes. The computed mechanism consists of two proton transfers and a hydrogen-atom transfer; the latter was the rate-determining step for all catalysts. The computational results were consistent with the experimental findings and rationalized the observed differences in the behavior of the metal catalysts. To be an efficient catalyst, a metal complex should satisfy the following criteria: moderate Brønsted and Lewis acidity (pKa=4-6), coordination with either water or weaker σ donors, energetically low-lying unoccupied orbitals, compact transition-state structures, and the ability for complexation of glucose. Thus, the reactivity of the metal catalysts in water is governed by many factors, not just the Lewis acidity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/chem.201402437
  • Recent achievements of electron beam deceleration method for FE-SEM enhanced elemental analysis including soft X-ray Emission Spectroscopy
    Asahina, S. and Sakuda, Y. and Murano, T. and Takahashi, H. and Kikuchi, N. and Kawauchi, K. and Nokuo, T. and Schüth, F. and Terasaki, O.
    Microscopy and Microanalysis 20 (2014)
    view abstract10.1017/S1431927614005157
  • Recent progress in scanning electron microscopy for the characterization of fine structural details of nano materials
    Suga, M. and Asahina, S. and Sakuda, Y. and Kazumori, H. and Nishiyama, H. and Nokuo, T. and Alfredsson, V. and Kjellman, T. and Stevens, S.M. and Cho, H.S. and Cho, M. and Han, L. and Che, S. and Anderson, M.W. and Schüth, F. and Deng, H. and Yaghi, O.M. and Liu, Z. and Jeong, H.Y. and Stein, A. and Sakamoto, K. and Ryoo, R. and Terasaki, O.
    Progress in Solid State Chemistry 42 (2014)
    Research concerning nano-materials (metal-organic frameworks (MOFs), zeolites, mesoporous silicas, etc.) and the nano-scale, including potential barriers for the particulates to diffusion to/from is of increasing importance to the understanding of the catalytic utility of porous materials when combined with any potential super structures (such as hierarchically porous materials). However, it is difficult to characterize the structure of for example MOFs via X-ray powder diffraction because of the serious overlapping of reflections caused by their large unit cells, and it is also difficult to directly observe the opening of surface pores using ordinary methods. Electron-microscopic methods including high-resolution scanning electron microscopy (HRSEM) have therefore become imperative for the above challenges. Here, we present the theory and practical application of recent advances such as through-the-lens detection systems, which permit a reduced landing energy and the selection of high-resolution, topographically specific emitted electrons, even from electrically insulating nano-materials. © 2014 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.progsolidstchem.2014.02.001
  • Synthesis of non-siliceous mesoporous oxides
    Gu, D. and Schüth, F.
    Chemical Society Reviews 43 (2014)
    Mesoporous non-siliceous oxides have attracted great interest due to their unique properties and potential applications. Since the discovery of mesoporous silicates in 1990s, organic-inorganic assembly processes by using surfactants or block copolymers as soft templates have been considered as a feasible path for creating mesopores in metal oxides. However, the harsh sol-gel conditions and low thermal stabilities have limited the expansion of this method to various metal oxide species. Nanocasting, using ordered mesoporous silica or carbon as a hard template, has provided possibilities for preparing novel mesoporous materials with new structures, compositions and high thermal stabilities. This review concerns the synthesis, composition, and parameter control of mesoporous non-siliceous oxides. Four synthesis routes, i.e. soft-templating (surfactants or block copolymers as templates), hard-templating (mesoporous silicas or carbons as sacrificial templates), colloidal crystal templating (3-D ordered colloidal particles as a template), and super lattice routes, are summarized in this review. Mesoporous metal oxides with different compositions have different properties. Non-siliceous mesoporous oxides are comprehensively described, including a discussion of constituting elements, synthesis, and structures. General aspects concerning pore size control, atomic scale crystallinity, and phase control are also reviewed. © 2014 The Royal Society of Chemistry.
    view abstract10.1039/c3cs60155b
  • An orders-of-magnitude increase in the rate of the solid-catalyzed co oxidation by in situ ball milling
    Immohr, S. and Felderhoff, M. and Weidenthaler, C. and Schüth, F.
    Angewandte Chemie - International Edition 52 (2013)
    Shaken, not stirred: CO oxidation was carried out continuously in a shaker ball mill. During milling, the reaction rate increases dramatically, but drops rapidly to zero when the mill is stopped. Compared to a conventional experiment in a plug-flow reactor, the rate of a ball-mill reaction catalyzed by Cr 2O3 is three orders of magnitude higher at room temperature and one order of magnitude higher at 100°C. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201305992
  • Colloidal deposition as method to study the influence of the support on the activity of gold catalysts in CO-oxidation
    Schüth, F.
    Physica Status Solidi (B) Basic Research 250 (2013)
    The strong influence of the support properties on the activity of gold catalysts has been observed in many publications. The most studied reaction in this respect seems to be CO-oxidation, for which gold catalysts have outstanding activity. However, since in most studies the support properties are also important in influencing the nature of the gold particles deposited on them by co-precipitation or deposition-precipitation, it is difficult to study the support effect alone. We have in a series of studies used colloidal impregnation of preformed gold particles approximately 3nm in size on different supports in order to decouple the gold particle formation from the deposition process, in order to isolate the support effect. Even for such similarly prepared catalysts very strong differences between different supports were observed. The analysis of the data, also in the light of literature data, suggests that there is no unique factor explaining the high activity of gold catalysts, but rather a combination of effects, which act in different proportion for different catalysts. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/pssb.201248499
  • Design of ordered mesoporous composite materials and their electrocatalytic activities for water oxidation
    Grewe, T. and Deng, X. and Weidenthaler, C. and Schüth, F. and Tüysüz, H.
    Chemistry of Materials 25 (2013)
    The controlled synthesis of a series of ordered mesoporous composite materials via solid-solid reaction of ordered mesoporous Co3O 4 with various transition metal precursors is reported. This versatile methodology allows preparation of a range of composites with precisely controllable material compositions. The textural parameters of the heterostructured compounds are highly dependent on the oxidation state of the dopant. Electrocatalytic activities of the prepared materials were investigated as oxygen evolution catalysts for the electrolysis of water. Among the ordered mesoporous composite materials, Co3O4-CuCo 2O4 shows a significant enhancement for electro-catalytic water splitting with a lower onset potential and higher current density. Following these results, a series of ordered mesoporous composite materials based on cobalt and copper oxides with different atomic ratios were prepared through a nanocasting route. Enhanced electrocatalytic performance was obtained for all composite samples in comparison with Co3O4. © 2013 American Chemical Society.
    view abstract10.1021/cm403153u
  • Diffraction and Spectroscopy of Porous Solids
    Schmidt, W. and Schüth, F. and Weidenthaler, C.
    Comprehensive Inorganic Chemistry II (Second Edition): From Elements to Applications 5 (2013)
    Porous solids are in the first place solids and thus all methods for the analysis of common solids can be also applied on porous ones. Structural information and bulk properties of the solid are accessible as for any other material. In addition, specific information on pore sizes, pore shapes, and properties of pore surfaces of such material can be obtained by different methods as well as information on guest species within the pores and on host-guest interactions. In the present chapter, diffraction and spectroscopic methods for the analysis of porous solids will be described and the type of information that can be achieved by the different methods will be illustrated. Diffraction and scattering of x-rays, neutrons, and electrons by a porous solid will be introduced as well as the application of infrared and nuclear magnetic resonance spectroscopy for the analysis of surface properties, host-guest interaction, and diffusion studies that are complemented by interference microscopy. © 2013 Elsevier Ltd. All rights reserved.
    view abstract10.1016/B978-0-08-097774-4.00501-5
  • Direct methane oxidation over Pt-modified nitrogen-doped carbons
    Soorholtz, M. and White, R.J. and Zimmermann, T. and Titirici, M.-M. and Antonietti, M. and Palkovits, R. and Schüth, F.
    Chemical Communications 49 (2013)
    Nitrogen-doped carbons derived from biomass precursors were modified with Pt2+ and successfully tested as solid catalysts in the direct oxidation of methane in fuming sulfuric acid. Remarkably, the catalytic performance was found to be substantially better than the Pt-modified Covalent Triazine Framework (CTF) system previously reported, although deactivation is more pronounced for the biomass derived catalyst supports. © 2013 The Royal Society of Chemistry.
    view abstract10.1039/c2cc36232e
  • Experimental and theoretical investigation of molybdenum carbide and nitride as catalysts for ammonia decomposition
    Zheng, W. and Cotter, T.P. and Kaghazchi, P. and Jacob, T. and Frank, B. and Schlichte, K. and Zhang, W. and Su, D.S. and Schüth, F. and Schlögl, R.
    Journal of the American Chemical Society 135 (2013)
    Constant COx-free H2 production from the catalytic decomposition of ammonia could be achieved over a high-surface-area molybdenum carbide catalyst prepared by a temperature-programmed reduction-carburization method. The fresh and used catalyst was characterized by N2 adsorption/desorption, powder X-ray diffraction, scanning and transmission electron microscopy, and electron energy-loss spectroscopy at different stages. Observed deactivation (in the first 15 h) of the high-surface-area carbide during the reaction was ascribed to considerable reduction of the specific surface area due to nitridation of the carbide under the reaction conditions. Theoretical calculations confirm that the N atoms tend to occupy subsurface sites, leading to the formation of nitride under an NH3 atmosphere. The relatively high rate of reaction (30 mmol/((g of cat.) min)) observed for the catalytic decomposition of NH3 is ascribed to highly energetic sites (twin boundaries, stacking faults, steps, and defects) which are observed in both the molybdenum carbide and nitride samples. The prevalence of such sites in the as-synthesized material results in a much higher H2 production rate in comparison with that for previously reported Mo-based catalysts. © 2013 American Chemical Society.
    view abstract10.1021/ja309734u
  • Mechanocatalytic depolymerization of cellulose combined with hydrogenolysis as a highly efficient pathway to sugar alcohols
    Hilgert, J. and Meine, N. and Rinaldi, R. and Schüth, F.
    Energy and Environmental Science 6 (2013)
    Cellulose is both insoluble in water and resistant against hydrolysis. These features pose major problems for its conversion into platform chemicals. Herein, we demonstrate that mechanocatalytic, solid-state depolymerization combined with hydrogenolysis, in the presence of Ru/C in water, provides a highly efficient pathway for the production of sugar alcohols. This novel approach leads to yields of hexitols up to 94% at 150 °C in an overall process time of 4 h. © The Royal Society of Chemistry 2013.
    view abstract10.1039/c2ee23057g
  • Mechanocatalytic depolymerization of dry (Ligno)cellulose as an entry process for high-yield production of furfurals
    Carrasquillo-Flores, R. and Käldström, M. and Schüth, F. and Dumesic, J.A. and Rinaldi, R.
    ACS Catalysis 3 (2013)
    Driven by mechanical forces, the acid-catalyzed depolymerization of solid biomass completely overcomes the problems posed by the recalcitrance of lignocellulose. The solid-state reaction leads to water-soluble oligosaccharides, which display higher reactivity than cellulose and hemicellulose. Here, we show that water-soluble oligosaccharides are useful feedstock for the high-yield production of 5-hydroxymethylfurfural (HMF) and furfural in biphasic reactors. This is because they readily undergo hydrolysis upon microwave heating, selectively forming monosaccharides as intermediates in the aqueous phase. Short reaction times are possible with the use of microwave heating and limit the extent of degradation reactions. This work provides an ionic-liquid-free approach to process lignocellulosic substrates into HMF and furfural with high yields. In fact, starting this novel approach with α-cellulose, yields of HMF of 79% and furfural of 80% at 443 K for 9 min were obtained. The processing of real lignocellulose (e.g., beechwood and sugar cane bagasse) also achieved high yields of HMF and furfural. Thereby, the current results indicate that the process limitation lies no longer in the recalcitrance of lignocellulose, but in the extraction of highly reactive HMF and furfural from the aqueous phase in the biphasic reactor. © 2013 American Chemical Society.
    view abstract10.1021/cs4001333
  • Molybdenum-based catalysts for the decomposition of ammonia: In situ X-ray diffraction studies, microstructure, and catalytic properties
    Tagliazucca, V. and Schlichte, K. and Schüth, F. and Weidenthaler, C.
    Journal of Catalysis 305 (2013)
    The ammonia decomposition reaction over molybdenum-based catalysts is an example for the complex influence of different factors, such as phase composition, size of crystalline domains, or defect concentration, on the catalytic behavior of a material. In situ powder diffraction allows the direct analysis of how catalysts change during a reaction with respect to the atomic structure or microstructure in terms of defects or size changes. In this article, the influence of catalyst treatment such as pre-reduction or ball milling on the catalytic properties is discussed in detail. © 2013 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.jcat.2013.05.011
  • Set of acidic resin catalysts to correlate structure and reactivity in fructose conversion to 5-hydroxymethylfurfural
    Richter, F.H. and Pupovac, K. and Palkovits, R. and Schüth, F.
    ACS Catalysis 3 (2013)
    A new synthetic route to acidic polystyrene-co-divinylbenzene resin catalysts allows systematic variation of cross-linker content, porosity, and acid site density. These resins are prepared in the form of powders by nanocasting, and the acid site density and the distribution of the acid sites in the prepared catalysts is controlled by liquid phase sulfonation with adjusted mixtures of sulfuric acid and oleum. This method allows identical synthesis conditions for the entire range of cross-linker content. With this set of model catalysts, the cross-linker content of the resin was found to be the most influential factor for the liquid phase dehydration of fructose to 5-hydroxymethylfurfural. © 2012 American Chemical Society.
    view abstract10.1021/cs3007439
  • Structural mimicking of inorganic catalyst supports with polydivinylbenzene to improve performance in the selective aerobic oxidation of ethanol and glycerol in water
    Richter, F.H. and Meng, Y. and Klasen, T. and Sahraoui, L. and Schüth, F.
    Journal of Catalysis 308 (2013)
    Many forms of polymers have been prepared and studied as polymeric catalyst support for metal nanoparticles and solid acid catalysts. The nanocasted mesoporous polydivinylbenzene (PDVB)-supported platinum catalysts presented here are distinguished by their customized mesoporosity and bulk morphology that are comparable to typical carbon-and alumina-supported powdered catalysts. Platinum nanoparticles are deposited on PDVB at loadings between 1 wt% and 9 wt% and a mean size between 2.7 nm and 6.2 nm, dependent on the synthesis method. Bifunctional catalysts containing platinum and acidic functionality are prepared by gas-phase sulfonation of the Pt/PDVB catalysts. The PDVB-supported catalysts are active for the oxidation of ethanol with molecular oxygen in water with up to 94% yield of acetic acid. In the analogous oxidation of glycerol, up to 60% yield of glyceric acid is reached with the bifunctional catalyst, and the polymer-supported catalysts feature lower formation of unidentified side products than Pt/C and Pt/Al2O3. Altogether, we find the polymers to be more active than the alumina and more selective than the carbon supports and thus overall have optimized performance. © 2013 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.jcat.2013.08.014
  • The formation of zeolites from solution - Analysis by mass spectrometry
    Lim, I.H. and Schrader, W. and Schüth, F.
    Microporous and Mesoporous Materials 166 (2013)
    Speciation of silicate in solution has been studied for a long time, but due to the complexity of such solutions, many questions are still open. A correlated problem, the mechanism of zeolite nucleation, remains one of the most challenging problems in zeolitic science. This is partly attributed to analytical limitations, which prevents the analysis of the crucial species involved in the process. Electrospray ionisation mass spectrometry (ESI-MS) has been successfully employed to monitor silicate speciation in prenucleating and nucleation zeolitic solutions. In this review, we present the application of mass spectrometry in studying zeolite formation. Discussion will include instrumentation, structural analysis by tandem mass spectrometry (MS/MS), dynamics of silicate species, heteroelement incorporation, and the study of nucleating solutions. © 2012 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.micromeso.2012.04.059
  • A crystal structure analysis and magnetic investigation on highly ordered mesoporous Cr 2O 3
    Tüysüz, H. and Weidenthaler, C. and Grewe, T. and Salabaş, E.L. and Benitez Romero, M.J. and Schüth, F.
    Inorganic Chemistry 51 (2012)
    A series of highly ordered mesoporous Cr 2O 3 were prepared through the nanocasting pathway from decomposition of chromium(VI) oxide using KIT-6 as a hard template. The effects of the calcination temperature on the crystal structure, textural parameters and magnetic properties of the material were investigated. It was found that with increasing calcination temperature, surface area and pore volume of the mesoporous Cr 2O 3 decreased slightly. Unpredictably, increasing calcination temperature also influences the lattice parameters of the Cr 2O 3 crystal, and this rearrangement in the lattice parameter leads to changes in the value of the Néel temperature. A spin-flop transition has been observed at a magnetic field smaller than that of bulk material. © 2012 American Chemical Society.
    view abstract10.1021/ic301671a
  • A strategy for the synthesis of mesostructured metal oxides with lower oxidation states
    Tüysüz, H. and Weidenthaler, C. and Schüth, F.
    Chemistry - A European Journal 18 (2012)
    A detailed study on the pseudomorphic conversion of ordered mesoporous Co 3O 4 and ferrihydrite into CoO and Fe 3O 4, respectively, by using alcohol/water vapor as a gentle reducing agent is described. The reduction conditions for the transformation were optimized. In addition, the first one-pot synthesis of mesostructured CoO by using nanocasting with cubic ordered silica as a hard template is demonstrated. As strong as an Ox: A detailed study on the pseudomorphic conversion of ordered mesoporous Co 3O 4 and ferrihydrite into CoO and Fe 3O 4, respectively, by using alcohol/water vapor as a gentle reducing agent is described. The reduction conditions for the transformation were optimized. In addition, the first one-pot synthesis of mesostructured CoO by using cubic ordered silica as a hard template is demonstrated. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/chem.201103650
  • Ammonia as a possible element in an energy infrastructure: Catalysts for ammonia decomposition
    Schüth, F. and Palkovits, R. and Schlögl, R. and Su, D.S.
    Energy and Environmental Science 5 (2012)
    The possible role of ammonia in a future energy infrastructure is discussed. The review is focused on the catalytic decomposition of ammonia as a key step. Other aspects, such as the catalytic removal of ammonia from gasification product gas or direct ammonia fuel cells, are highlighted as well. The more general question of the integration of ammonia in an infrastructure is also covered. © 2012 The Royal Society of Chemistry.
    view abstract10.1039/c2ee02865d
  • Au, @ZrO 2 yolk-shell catalysts for CO oxidation: Study of particle size effect by ex-post size control of Au cores
    Güttel, R. and Paul, M. and Galeano, C. and Schüth, F.
    Journal of Catalysis 289 (2012)
    Gold nanoparticles supported on transition metal oxides are found to exhibit a pronounced particle size effect in CO oxidation. However, the preparation of comparable supported gold nanoparticles with different sizes remains challenging, since the catalytic behavior of these materials is very sensitive to the preparation conditions. To overcome this difficulty, Au, @ZrO 2 catalysts with gold core sizes between 5 and 15 nm were prepared by partial leaching of gold in an ex-post manner. The material obtained offers a unique comparability for particle size effect studies in CO oxidation. No effect of gold particle size was observed in the studied size range. © 2012 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.jcat.2012.01.021
  • Chemistry of materials-your journal for high science in 2012
    Schüth, F.
    Chemistry of Materials 24 (2012)
    view abstract10.1021/cm2032948
  • Degradation mechanisms of Pt/C fuel cell catalysts under simulated start-stop conditions
    Meier, J.C. and Galeano, C. and Katsounaros, I. and Topalov, A.A. and Kostka, A. and Schüth, F. and Mayrhofer, K.J.J.
    ACS Catalysis 2 (2012)
    This manuscript investigates the degradation of a Pt/Vulcan fuel cell catalyst under simulated start-stop conditions in an electrochemical half-cell. Identical location transmission electron microscopy (IL-TEM) is used to visualize the several different degradation pathways occurring on the same catalyst material under potential cycling conditions. The complexity of degradation on the nanoscale leading to macroscopic active surface area lossis demonstrated and discussed. Namely, four different degradation pathways at one single Pt/Vulcan aggregate are clearly observed. Furthermore, inhomogeneous degradation behavior for different catalyst locations is shown, and trends in degradation mechanisms related to the platinum particle size are discussed in brief. Attention is drawn to the vast field of parameters influencing catalyst stability. We also present the development of a new technique to study changes of the catalyst not only with 2D projections of standard TEM images but also in 3D. For this purpose, identical location tomography (IL-tomography) is introduced, which visualizes the 3D structure of an identical catalyst location before and after degradation. © 2012 American Chemical Society.
    view abstract10.1021/cs300024h
  • One-pot synthesis of mesoporous Cu-γ-Al 2O 3 as bifunctional catalyst for direct dimethyl ether synthesis
    Jiang, H. and Bongard, H. and Schmidt, W. and Schüth, F.
    Microporous and Mesoporous Materials 164 (2012)
    Mesoporous copper-alumina (Cu-Al 2O 3) with different copper contents was synthesized in a one-pot reaction via the evaporation-induced self-assembly of Pluronic P123 and the corresponding metal precursors in ethanolic solution in the presence of nitric acid. Mesoporous Cu-Al 2O 3 calcined at 400°C exhibits a large BET surface area of 265 m 2/g and a pore volume of 0.48 cm 3/g. XRD results indicate that the wall of mesoporous Cu-Al 2O 3 calcined at 400°C is amorphous, and that it is transformed to crystalline material by further thermal treatment at 800°C. Copper was formed as very small particles in the composite under 5% H 2 flow at high temperature. Moreover, the mesoporous structure did not collapse after the sample was reduced at 650°C for 4 h, and the copper particles with sizes of around 6 nm were well distributed through the entire mesoporous γ-Al 2O 3 network. Using the mesoporous Cu/γ-Al 2O 3 as a bifunctional catalyst for one-step dimethyl ether synthesis from synthesis gas, a CO conversion of 72% and a DME selectivity of 69% were obtained at 50 bar and 310°C. © 2012 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.micromeso.2012.08.004
  • Ordered Mesoporous Materials as Catalysts
    Tüysüz, H. and Schüth, F.
    Advances in Catalysis 55 (2012)
    After their discovery in the early 1990s, ordered mesoporous materials have become one of the most widely investigated classes of materials, and applications have been considered in many areas, in particular in catalysis. They have attracted attention because of their unique properties such as high surface areas, controllable compositions, crystallinity, thermal and chemical stability, tailored porosities, narrow pore size distributions, concave surface curvatures, surface functionalities, as well as the opportunities they offer for incorporation of catalytically active and selective species. This chapter is focused on the properties of ordered mesoporous solids that distinguish them from more conventional porous catalytic materials. Emphasis is placed on history, development, and methods of synthesis of ordered mesoporous materials. © 2012 Elsevier Inc..
    view abstract10.1016/B978-0-12-385516-9.00002-8
  • Size-controlled synthesis and microstructure investigation of Co 3O 4 nanoparticles for low-temperature CO oxidation
    Dangwal Pandey, A. and Jia, C. and Schmidt, W. and Leoni, M. and Schwickardi, M. and Schüth, F. and Weidenthaler, C.
    Journal of Physical Chemistry C 116 (2012)
    Noble-metal-free functional oxides are active catalysts for CO oxidation at low temperatures. Spinel-type cobalt oxide (Co 3O 4) nanoparticles can be easily synthesized by impregnation of activated carbon with concentrated cobalt nitrate and successive carbon burn off. Mean size and particle size distribution can be tuned by adding small amounts of silica to the carbon precursor, as witnessed by whole powder pattern modeling of the X-ray powder diffraction data. The catalytic tests performed after silica removal show a significant influence of the mean domain size and of size distribution on the CO oxidation activity of the individual Co 3O 4 specimens, whereas defects play a less important role in the present case. © 2012 American Chemical Society.
    view abstract10.1021/jp306166g
  • Solvent-Free catalytic depolymerization of cellulose to water-soluble oligosaccharides
    Meine, N. and Rinaldi, R. and Schüth, F.
    ChemSusChem 5 (2012)
    The use of cellulose is hampered by difficulties with breaking up the biopolymer into soluble products. Herein, we show that the impregnation of cellulosic substrates with catalytic amounts of a strong acid (e.g., H 2SO 4, HCl) is a highly effective strategy for minimizing the contact problem commonly experienced in mechanically assisted, solid-state reactions. Milling the acid-impregnated cellulose fully converts the substrate into water-soluble oligosaccharides within 2a H. In aqueous solution, soluble products are easily hydrolyzed at 130°C in 1a H, leading to 91% conversion of the glucan fraction of α-cellulose into glucose, and 96% of the xylans into xylose. Minor products are glucose dimers (8%), 5-hydroxymethylfurfural (1%) and furfural (4%). Milling practical feedstocks (e.g., wood, sugarcane bagasse, and switchgrass) also results to water-soluble products (oligosaccharides and lignin fragments). The integrated approach (solid-state depolymerization in combination with liquid-phase hydrolysis) could well hold the key to a highly efficient "entry process" in biorefinery schemes. Reactive milling: Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cssc.201100770
  • Stability investigations of electrocatalysts on the nanoscale
    Meier, J.C. and Katsounaros, I. and Galeano, C. and Bongard, H.J. and Topalov, A.A. and Kostka, A. and Karschin, A. and Schüth, F. and Mayrhofer, K.J.J.
    Energy and Environmental Science 5 (2012)
    The search for more stable electrocatalyst materials for electrochemical energy conversion requires a fundamental understanding of the underlying degradation processes. Advanced characterization techniques like identical location transmission electron microscopy (IL-TEM) can provide invaluable insight into the stability of electrode materials on the nanoscale. In this review, the basic principles and the methodology of IL-TEM are described, and its capabilities are revealed by demonstrating the recent progress that has been achieved in research on the stability of fuel cell catalysts. Moreover, we provide future perspectives of the identical location approach towards implementing other electron microscopic and tomographic applications, which will help us to gain an even broader view of the degradation of electrocatalysts. © 2012 The Royal Society of Chemistry.
    view abstract10.1039/c2ee22550f
  • Surface Diels-Alder reactions as an effective method to synthesize functional carbon materials
    Kaper, H. and Grandjean, A. and Weidenthaler, C. and Schüth, F. and Goettmann, F.
    Chemistry - A European Journal 18 (2012)
    The post-synthesis chemical modification of various porous carbon materials with unsaturated organic compounds is reported. By this method, amine, alcohol, carboxylate, and sulfonic acid functional groups can be easily incorporated into the materials. Different carbonaceous materials with surface areas ranging from 240 to 1500 m 2 g -1 and pore sizes between 3.0 and 7.0 nm have been studied. The resulting materials were analyzed by elemental analysis, nitrogen sorption, FTIR spectroscopy, zeta-potential measurements, thermogravimetric analysis, photoelectron spectroscopy, and small-angle X-ray scattering. These analyses indicated that the degree of functionalization is dependent on the nature of the dienophile (reactivity, steric hindrance) and the porosity of the carbon material. As possible applications, the functionalized carbonaceous materials were studied as catalysts in the Knoevenagel reaction and as adsorbents for Pb 2+ from aqueous solution. Making grafting on carbon as easy as grafting on silica? A new and easy approach, based on surface Diels-Alder reactions, allows the introduction of organic functionalities into the framework of mesoporous carbon (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/chem.201102718
  • Synthesis of hard magnetic ordered mesoporous Co3O 4/CoFe2O4 nanocomposites
    Tüysüz, H. and Salabaş, E.L. and Bill, E. and Bongard, H. and Spliethoff, B. and Lehmann, C.W. and Schüth, F.
    Chemistry of Materials 24 (2012)
    The nanocomposite Co3O4/CoFe2O4 heterostructured mesoporous material was produced via a simple solid-solid reaction of an iron precursor with ordered mesoporous Co3O 4 that had been prepared via nanocasting from mesoporous silica as hard template. The magnetic behavior of the exchange-coupled antiferromagnetic/ferrimagnetic (AFM/FM) system was investigated via superconducting quantum interference device (SQUID) magnetometry and 57Fe Mössbauer spectroscopy. The low-temperature magnetization loops of the Co3O4/CoFe2O4 heterostructure present exchange bias under cooling in an applied magnetic field. The antiferromagnetic ordering temperature of Co3O4 is increased due to the proximity of the hard magnetic CoFe2O 4 phase. The nanocomposite Co3O4/CoFe 2O4 behaves as an exchange coupled system with a cooperative magnetic switching. © 2012 American Chemical Society.
    view abstract10.1021/cm3005166
  • Synthesis, crystal structures, and hydrogen-storage properties of Eu(AlH 4) 2 and Sr(AlH 4) 2 and of their decomposition intermediates, EuAlH 5 and SrAlH 5
    Pommerin, A. and Wosylus, A. and Felderhoff, M. and Schüth, F. and Weidenthaler, C.
    Inorganic Chemistry 51 (2012)
    Complex Eu(AlH 4) 2 and Sr(AlH 4) 2 hydrides have been prepared by a mechanochemical metathesis reaction from NaAlH 4 and europium or strontium chlorides. The crystal structures were solved from powder X-ray diffraction data in combination with solid-state 27Al NMR spectroscopy. The thermolysis pathway was analyzed in detail, allowing identification of new intermediate EuAlH 5/SrAlH 5 compounds. Rehydrogenation experiments indicate that the second decomposition step is reversible. © 2012 American Chemical Society.
    view abstract10.1021/ic202492v
  • Toward highly stable electrocatalysts via nanoparticle pore confinement
    Galeano, C. and Meier, J.C. and Peinecke, V. and Bongard, H. and Katsounaros, I. and Topalov, A.A. and Lu, A. and Mayrhofer, K.J.J. and Schüth, F.
    Journal of the American Chemical Society 134 (2012)
    The durability of electrode materials is a limiting parameter for many electrochemical energy conversion systems. In particular, electrocatalysts for the essential oxygen reduction reaction (ORR) present some of the most challenging instability issues shortening their practical lifetime. Here, we report a mesostructured graphitic carbon support, Hollow Graphitic Spheres (HGS) with a specific surface area exceeding 1000 m2 g-1 and precisely controlled pore structure, that was specifically developed to overcome the long-term catalyst degradation, while still sustaining high activity. The synthetic pathway leads to platinum nanoparticles of approximately 3 to 4 nm size encapsulated in the HGS pore structure that are stable at 850 C and, more importantly, during simulated accelerated electrochemical aging. Moreover, the high stability of the cathode electrocatalyst is also retained in a fully assembled polymer electrolyte membrane fuel cell (PEMFC). Identical location scanning and scanning transmission electron microscopy (IL-SEM and IL-STEM) conclusively proved that during electrochemical cycling the encapsulation significantly suppresses detachment and agglomeration of Pt nanoparticles, two of the major degradation mechanisms in fuel cell catalysts of this particle size. Thus, beyond providing an improved electrocatalyst, this study describes the blueprint for targeted improvement of fuel cell catalysts by design of the carbon support. © 2012 American Chemical Society.
    view abstract10.1021/ja308570c
  • A facile synthesis of shape- and size-controlled α-Fe 2O3 nanoparticles through hydrothermal method
    Wang, G.-H. and Li, W.-C. and Jia, K.-M. and Lu, A.-H. and Feyen, M. and Spliethoff, B. and SchÜth, F.
    Nano 6 (2011)
    α-Fe2O3 nanoparticles have wide-ranging applications such as in catalysis, sensoring, painting, etc. This is the reason to study their controlled synthesis. Here we have investigated the synthesis of uniform α-Fe2O3 nanoparticles using amino acids as morphology control agents. The products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA). It was found that the type and the amount of amino acids as well as the reaction temperatures have significant influence on the shape and size of the obtained α-Fe2O3 nanoparticles. The use of acidic amino acids (always contain C=O in the side chain) typically leads to the formation of α-Fe2O3 nanoparticles with spindle shape. However, rhombohedrally shaped α-Fe 2O3 nanoparticles were formed in presence of basic amino acids (always contain -NH2 in the side chain). Increasing the amount of amino acid generally results in α-Fe2O3 nanoparticles with decreasing particle sizes. © 2011 World Scientific Publishing Company.
    view abstract10.1142/S1793292011002846
  • A new HRSEM approach to observe fine structures of novel nanostructured materials
    Asahina, S. and Uno, S. and Suga, M. and Stevens, S.M. and Klingstedt, M. and Okano, Y. and Kudo, M. and Schüth, F. and Anderson, M.W. and Adschiri, T. and Terasaki, O.
    Microporous and Mesoporous Materials 146 (2011)
    A new approach for observing fine structures of novel thin, nanostructured materials called through the lens system (TTLS) is employed to observe interesting features on a variety of new, catalytically-important, hierarchically porous rattlespheres. © 2011 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.micromeso.2011.06.010
  • Activity improvement of gold yolk-shell catalysts for CO oxidation by doping with TiO2
    Güttel, R. and Paul, M. and Schüth, F.
    Catalysis Science and Technology 1 (2011)
    Au, ZrO2 yolk-shell catalysts were found to exhibit a surprisingly high activity in CO oxidation even though the gold particle size is about 15 nm. A further enhancement of the activity has been achieved by simply doping these materials with small amounts of TiO2 during synthesis. A comparison of the standard Au, @ZrO2 yolk-shell catalysts with the novel TiO2-doped Au/Ti, @ZrO2 shows significant activity enhancement, even though small amounts of TiO2 are present. © 2011 The Royal Society of Chemistry.
    view abstract10.1039/c0cy00026d
  • Chemical compounds for energy storage
    Schüth, F.
    Chemie-Ingenieur-Technik 83 (2011)
    Future energy systems, which will rely on substantially higher contributions from regenerative supply pathways and which will be increasingly less dependent on fossil energy resources, will require high energy density storage compounds as strategic reserves and for seasonal storage. Hydrocarbons, such as oil and natural gas, are currently serving this purpose. These will also be options in future systems, but in that case, these compounds would have to be synthesized using some other form of energy. Thus, with decreasing importance of fossil resources, other storage compounds also seem to be viable, the most prominent ones under discussion, in addition to the ones mentioned, being hydrogen, methanol, and ethanol. In this contribution, the different storage compounds will be discussed, and their merits and drawbacks for large scale implementation will be compared. The intensified use of renewable sources in future energy systems implies the demand for high density storage compounds. Hydrogen, methane, liquid hydrocarbons, methanol, and ethanol are potential candidates for that purpose. The different storage compounds are discussed and their advantages and drawbacks are compared. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cite.201100147
  • Co3O4 - SiO2 Nanocomposite: A very active catalyst for co oxidation with unusual catalytic behavior
    Jia, C.-J. and Schwickardi, M. and Weidenthaler, C. and Schmidt, W. and Korhonen, S. and Weckhuysen, B.M. and Schüth, F.
    Journal of the American Chemical Society 133 (2011)
    A high surface area Co3O4 - SiO2 nanocomposite catalyst has been prepared by use of activated carbon as template. The Co3O4 - SiO2 composite, the surface of which is rich in silica and Co(II) species compared with normal Co 3O4, exhibited very high activity for CO oxidation even at a temperature as low as '76 °C. A rather unusual temperature-dependent activity curve, with the lowest conversion at about 80 °C, was observed with a normal feed gas (H2O content 3 ppm). The U-shape of the activity curve indicates a negative apparent activation energy over a certain temperature range, which has rarely been observed for the heterogeneously catalyzed oxidation of CO. Careful investigation of the catalytic behavior of Co 3O4 - SiO2 catalyst led to the conclusion that adsorption of H2O molecules on the surface of the catalyst caused the unusual behavior. This conclusion was supported by in situ diffuse reflectance Fourier transform infrared (DRIFT) spectroscopic experiments under both normal and dry conditions. © 2011 American Chemical Society.
    view abstract10.1021/ja2028926
  • Colloidal metal nanoparticles as a component of designed catalyst
    Jia, C.-J. and Schüth, F.
    Physical Chemistry Chemical Physics 13 (2011)
    Recent advances in the synthesis of collidal metal nanoparticles of controlled sizes and shapes that are relevant for catalyst design are reviewed. Three main methods, based on colloid chemistry techniques in solution, i.e., chemical reduction of metal salt precursors, electrochemical synthesis, and controlled decomposition of organometallic compounds and metal-surfactant complexes, are used to synthesize metal nanoparticles. Their catalytic activity and selectivity depend on the shape, size and composition of the metal nanoparticles, and the support effect, as shown for many reactions in quasi-homogeneous and heterogeneous catalysis. A specially designed type of thermally stable catalysts - "embedded" metal catalysts, in which metal nanoparticles are isolated by porous support shells so that metal sintering is effectively avoided at high temperatures, are also introduced. The ultilization of pre-prepared colloidal metal nanoparticles with tuned size, shape and composition as components of designed catalysts opens up new field in catalysis. © 2011 the Owner Societies.
    view abstract10.1039/c0cp02680h
  • Controlled nanostructures for applications in catalysis
    Schüth, F.
    Physical Chemistry Chemical Physics 13 (2011)
    view abstract10.1039/c1cp90005f
  • Fingerprinting the magnetic behavior of antiferromagnetic nanostructures using remanent magnetization curves
    Benitez, M.J. and Petracic, O. and Tüysüz, H. and Schüth, F. and Zabel, H.
    Physical Review B - Condensed Matter and Materials Physics 83 (2011)
    Antiferromagnetic (AF) nanostructures from Co3O4, CoO, and Cr2O3 were prepared by the nanocasting method and were characterized magnetometrically. The field- and temperature-dependent magnetization data suggests that the nanostructures consist of a core-shell structure. The core behaves as a regular antiferromagnet and the shell as a two-dimensional diluted antiferromagnet in a field (2D DAFF) as previously shown on Co3O4 nanowires. Here we present a more general picture on three different material systems, i.e., Co3O4, CoO, and Cr2O3. In particular, we consider the thermoremanent (TRM) and the isothermoremanent (IRM) magnetization curves as "fingerprints" in order to identify the irreversible magnetization contribution originating from the shells. The TRM/IRM fingerprints are compared to those of superparamagnetic systems, superspin glasses, and 3D DAFFs. We demonstrate that TRM/IRM vs H plots are generally useful fingerprints to identify irreversible magnetization contributions encountered in particular in nanomagnets. © 2011 American Physical society.
    view abstract10.1103/PhysRevB.83.134424
  • High-temperature stable, iron-based core-shell catalysts for ammonia decomposition
    Feyen, M. and Weidenthaler, C. and Güttel, R. and Schlichte, K. and Holle, U. and Lu, A.-H. and Schüth, F.
    Chemistry - A European Journal 17 (2011)
    High-temperature, stable core-shell catalysts for ammonia decomposition have been synthesized. The highly active catalysts, which were found to be also excellent model systems for fundamental studies, are based on α-Fe 2O 3 nanoparticles coated by porous silica shells. In a bottom-up approach, hematite nanoparticles were firstly obtained from the hydrothermal reaction of ferric chlorides, L-lysine, and water with adjustable average sizes of 35, 47, and 75nm. Secondly, particles of each size could be coated by a porous silica shell by means of the base-catalyzed hydrolysis of tetraethylorthosilicate (TEOS) with cetyltetramethylammonium bromide (CTABr) as porogen. After calcination, TEM, high-resolution scanning electron microscopy (HR-SEM), energy-dispersive X-ray (EDX), XRD, and nitrogen sorption studies confirmed the successful encapsulation of hematite nanoparticles inside porous silica shells with a thickness of 20nm, thereby leading to composites with surface areas of approximately 380 m 2g -1 and iron contents between 10.5 and 12.2wt%. The obtained catalysts were tested in ammonia decomposition. The influence of temperature, iron oxide core size, possible diffusion limitations, and dilution effects of the reagent gas stream with noble gases were studied. The catalysts are highly stable at 750°C with a space velocity of 120000 cm 3 g cat -1h -1 and maintained conversions of around 80% for the testing period time of 33 h. On the basis of the excellent stability under reaction conditions up to 800°C, the system was investigated by in situ XRD, in which body-centered iron was determined, in addition to FeN x, as the crystalline phase under reaction conditions above 650deg;C. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/chem.201001827
  • HT-PEM fuel cell system with integrated complex metal hydride storage tank
    Urbanczyk, R. and Peil, S. and Bathen, D. and Heßke, C. and Burfeind, J. and Hauschild, K. and Felderhoff, M. and Schüth, F.
    Fuel Cells 11 (2011)
    A hydrogen storage tank based on the metal hydride sodium alanate is coupled with a high temperature PEM fuel cell (HT-PEM). The waste heat of the fuel cell is used for desorbing hydrogen from the storage tank that in return feeds the fuel cell. ZBT has developed the HT-PEM fuel cell, Max-Planck-Institut für Kohlenforschung the sodium alanate, and IUTA the hydrogen storage tank. During the experiments of the system the fuel cell was operated by load cycling from 165 up to 240 W. Approximately 60 g of hydrogen were delivered from the tank, which was charged with 2676.8 g of sodium alanate doped with 4 mol.% of TiCl 3. This amount of hydrogen was desorbed in 3 h and generated a cumulated electrical energy of 660 Wh. In the first cycle 81.5 g of hydrogen were supplied during 3.69 h to the HT-PEM fuel cell, which was operated nearly constant at 260 W. In the latter case the cumulated electrical energy was 941 Wh. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/fuce.201100012
  • Hydrogen storage properties of nanostructured MgH2/TiH 2 composite prepared by ball milling under high hydrogen pressure
    Shao, H. and Felderhoff, M. and Schüth, F.
    International Journal of Hydrogen Energy 36 (2011)
    Nanostructured MgH2/0.1TiH2 composite was synthesized directly from Mg and Ti metal by ball milling under an initial hydrogen pressure of 30 MPa. The synthesized composite shows interesting hydrogen storage properties. The desorption temperature is more than 100 °C lower compared to commercial MgH2 from TG-DSC measurements. After desorption, the composite sample absorbs hydrogen at 100 °C to a capacity of 4 mass% in 4 h and may even absorb hydrogen at 40 °C. The improved properties are due to the catalyst and nanostructure introduced during high pressure ball milling. From the PCI results at 269, 280, 289 and 301 °C, the enthalpy change and entropy change during the desorption can be determined according to the van't Hoff equation. The values for the MgH2/0.1TiH2 nano-composite system are 77.4 kJ mol-1 H2 and 137.5 J K-1 mol-1 H2, respectively. These values are in agreement with those obtained for a commercial MgH2 system measured under the same conditions. Nanostructure and catalyst may greatly improve the kinetics, but do not change the thermodynamics of the materials. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.ijhydene.2011.05.180
  • Nanostructured Ti-catalyzed MgH2 for hydrogen storage
    Shao, H. and Felderhoff, M. and Schüth, F. and Weidenthaler, C.
    Nanotechnology 22 (2011)
    Nanocrystalline Ti-catalyzed MgH2 can be prepared by a homogeneously catalyzed synthesis method. Comprehensive characterization of this sample and measurements of hydrogen storage properties are discussed and compared to a commercial MgH2 sample. The catalyzed MgH2 nanocrystalline sample consists of two MgH2 phases-a tetrahedral β-MgH2 phase and an orthorhombic high-pressure modification γ-MgH2. Transmission electron microscopy was used for the observation of the morphology of the samples and to confirm the nanostructure. N2 adsorption measurement shows a BET surface area of 108m 2g-1 of the nanostructured material. This sample exhibits a hydrogen desorption temperature more than 130 °C lower compared to commercial MgH2. After desorption, the catalyzed nanocrystalline sample absorbs hydrogen 40 times faster than commercial MgH2 at 300 °C. Both the Ti catalyst and the nanocrystalline structure with correspondingly high surface area are thought to play important roles in the improvement of hydrogen storage properties. The desorption enthalpy and entropy values of the catalyzed MgH2 nanocrystalline sample are 77.7kJmol-1H2 and 138.3JK-1mol -1H2, respectively. Thermodynamic properties do not change with the nanostructure. © 2011 IOP Publishing Ltd.
    view abstract10.1088/0957-4484/22/23/235401
  • Structurally designed synthesis of mechanically stable poly(benzoxazine-co- resol)-based porous carbon monoliths and their application as high-performance CO2 capture sorbents
    Hao, G.-P. and Li, W.-C. and Qian, D. and Wang, G.-H. and Zhang, W.-P. and Zhang, T. and Wang, A.-Q. and Schüth, F. and Bongard, H.-J. and Lu, A.-H.
    Journal of the American Chemical Society 133 (2011)
    Porous carbon monoliths with defined multilength scale pore structures, a nitrogen-containing framework, and high mechanical strength were synthesized through a self-assembly of poly(benzoxazine-co-resol) and a carbonization process. Importantly, this synthesis can be easily scaled up to prepare carbon monoliths with identical pore structures. By controlling the reaction conditions, porous carbon monoliths exhibit fully interconnected macroporosity and mesoporosity with cubic Im3m symmetry and can withstand a press pressure of up to 15.6 MPa. The use of amines in the synthesis results in a nitrogen-containing framework of the carbon monolith, as evidenced by the cross-polarization magic-angle-spinning NMR characterization. With such designed structures, the carbon monoliths show outstanding CO2 capture and separation capacities, high selectivity, and facile regeneration at room temperature. At 1 bar, the equilibrium capacities of the monoliths are in the range of 3.3 - 4.9 mmol g- 1 at 0 °C and of 2.6 - 3.3 mmol g - 1 at 25 °C, while the dynamic capacities are in the range of 2.7 - 4.1 wt % at 25 °C using 14% (v/v) CO2 in N2. The carbon monoliths exhibit high selectivity for the capture of CO2 over N2 from a CO2/N2 mixture, with a separation factor ranging from 13 to 28. Meanwhile, they undergo a facile CO2 release in an argon stream at 25 °C, indicating a good regeneration capacity. © 2011 American Chemical Society.
    view abstract10.1021/ja203857g
  • The role of the synthesis method in the structure formation of cobalt aluminate
    Onfroy, T. and Li, W.-C. and Schüth, F. and Knözinger, H.
    Topics in Catalysis 54 (2011)
    Cobalt aluminate (spinel) was prepared via two synthesis routes firstly a co-precipitation method and secondly a nanocasting method. The surface chemistry of these materials was characterized by infrared-spectroscopy of the surface hydroxyl groups and of coordinatively unsaturated (cus) cations (Al and Co) by carbon monoxide CO at low temperature. The goal was to investigate whether or not the preparation of the spinel phase had an effect on this structural characteristics, namely on the inversion degree. The hydroxyl (deuteroxyl) spectra were characterized by six types of O-H stretching bands. While the O-H stretching frequencies were identical for both materials, the relative intensities of the bands were clearly different indicating a distinct distribution of the different types of hydroxyl groups which most likely originates from a distinct distribution of the cations in the two differently synthesized materials. The preparation method obviously yields spinel structures having variable degrees of inversion. Coordinatively unsaturated cus cations are exposed on the surface during the removal of O-H groups by thermal dehydroxylation. Those Lewis acid centers show an acid strength distribution which is again an indication for formation of two distinct degrees of inversion. © 2011 Springer Science+Business Media, LLC.
    view abstract10.1007/s11244-011-9669-y
  • Yolk-shell gold nanoparticles as model materials for support-effect studies in heterogeneous catalysis: Au, @C and Au, @ZrO2 for CO oxidation as an example
    Galeano, C. and Güttel, R. and Paul, M. and Arnal, P. and Lu, A.-H. and Schüth, F.
    Chemistry - A European Journal 17 (2011)
    The use of nanostructured yolk-shell materials offers a way to discriminate support and particle-size effects for mechanistic studies in heterogeneous catalysis. Herein, gold yolk-shell materials have been synthesized and used as model catalysts for the investigation of support effects in CO oxidation. Carbon has been selected as catalytically inert support to study the intrinsic activity of the gold nanoparticles, and for comparison, zirconia has been used as oxidic support. Au, @C materials have been synthesized through nanocasting using two different nonporous-core@mesoporous-shell exotemplates: Au@SiO 2@ZrO2 and Au@SiO2@m-SiO2. The catalytic activity of Au, @C with a gold core of about 14nm has been evaluated and compared with Au, @ZrO2 of the same gold core size. The strong positive effect of metal oxide as support material on the activity of gold has been proved. Additionally, size effects were investigated using carbon as support to determine only the contribution of the nanoparticle size on the catalytic activity of gold. Therefore, Au, @C with a gold core of about 7nm was studied showing a less pronounced positive effect on the activity than the metal oxide support effect. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/chem.201100318
  • Accessing ultrashort reaction times in particle formation with SAXS experiments: ZnS precipitation on the microsecond time scale
    Schmidt, W. and Bussian, P. and Lindén, M. and Amenitsch, H. and Agren, P. and Tiemann, M. and Schüth, F.
    Journal of the American Chemical Society 132 (2010)
    Precipitation of zinc sulfide particles is a very rapid process, and monitoring of the particle growth is experimentally very demanding. Applying a liquid jet flow cell, we were able to follow zinc sulfide particle formation on time scales down to 10 -5 s. The flow cell was designed in such a way that data acquisition on the microsecond time scale was possible under steady-state conditions along a liquid jet (tubular reactor concept), allowing SAXS data accumulation over a time scale of minutes. We were able to monitor the growth of zinc sulfide particles and found experimental evidence for very rapid particle aggregation processes within the liquid jet. Under the experimental conditions the particle growth is controlled by mass transfer: i.e., the diffusion of the hydrogen sulfide into the liquid jet. © 2010 American Chemical Society.
    view abstract10.1021/ja101519z
  • An aqueous emulsion route to synthesize mesoporous carbon vesicles and their nanocomposites
    Gu, D. and Bongard, H. and Deng, Y. and Feng, D. and Wu, Z. and Fang, Y. and Mao, J. and Tu, B. and Schüth, F. and Zhao, D.
    Advanced Materials 22 (2010)
    Onionlike mesoporous carbon and carbonsilica nanocomposites with multilayer vesicle structures can be synthesized by an organic-inorganic co-assembly method under hydrothermal conditions in an aqueous emulsion solution (see figure). The nanocomposite vesicles have ordered lamellar mesostructures with about 3-9 layers and carbon pillars are located between the neighboring shells. (Chemical Equation Persentation). © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.
    view abstract10.1002/adma.200902550
  • An integrated catalytic approach to fermentable sugars from cellulose
    Rinaldi, R. and Engel, P. and Büchs, J. and Spiess, A.C. and Schüth, F.
    ChemSusChem 3 (2010)
    The production of fermentable sugars from cellulose in almost quantitative yield is accelerated. Starting from cello-oligomers obtained by acid hydrolysis of cellulose in an ionic liquid, the catalytic approach described herein, integrating acid and enzymatic catalysis, quantitatively converts cellulose to fermentable sugars (glucose and cellobiose) within only a few hours. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cssc.201000153
  • Cross-metathesis as a versatile tool for reversible surface modifications
    Palkovits, R. and Arlt, D. and Stepowska, H. and Schüth, F.
    Microporous and Mesoporous Materials 132 (2010)
    Cross-metathesis can be used as a versatile tool to reversibly modify support materials with molecules bearing different functionalities. Two approaches, applying cross-metathesis either inside the pore system of SBA-15 as support material or in the liquid-phase prior to immobilization on the support, have been compared. Special attention is focussed on pitfalls and limitations of surface modifications inside the pore system of support materials and on strategies to overcome these challenges. The optimized immobilization procedure was successfully transferred to the reversible immobilization of a molecular catalyst. © 2010 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.micromeso.2010.03.008
  • Development of molecular and solid catalysts for the direct low-temperature oxidation of methane to methanol
    Palkovits, R. and von Malotki, C. and Baumgarten, M. and Müllen, K. and Baltes, C. and Antonietti, M. and Kuhn, P. and Weber, J. and Thomas, A. and Schüth, F.
    ChemSusChem 3 (2010)
    The direct low-temperature oxidation of methane to methanol is demonstrated on a highly active homogeneous molecular catalyst system and on heterogeneous molecular catalysts based on polymeric materials possessing ligand motifs within the material structure. The N-(2-methylpropyl)-4,5-diazacarbazolyl-dichloro-platinum(II) complex reaches significantly higher activity compared to the well-known Periana system and allows first conclusions on electronic and structural requirements for high catalytic activity in this reaction. Interestingly, comparable activities could be achieved utilizing a platinum modified poly(benzimidazole) material, which demonstrates for the first time a solid catalyst with superior activity compared to the Periana system. Although the material shows platinum leaching, improved activity and altered electronic properties, compared to the conventional Periana system, support the proposed conclusions on structure-activity relationships. In comparison, platinum modified triazine-based catalysts show lower catalytic activity, but rather stable platinum coordination even after several catalytic cycles. Based on these systems, further development of improved solid catalysts for the direct low-temperature oxidation of methane to methanol is feasible. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cssc.200900123
  • Direct synthesis of pure complex aluminium hydrides by cryomilling
    Pommerin, A. and Weidenthaler, C. and Schüth, F. and Felderhoff, M.
    Scripta Materialia 62 (2010)
    Simple mechanochemical procedures can be used for the solid-state preparation of stable complex aluminium hydrides as hydrogen storage materials. For the synthesis of unstable complex hydrides, cryomilling at temperatures at which product decomposition does not take place under milling conditions appears to be a viable method. To probe the potential of cryomilling for the synthesis of complex aluminium hydrides, the reactions of different alkaline hydrides with AlH3 were tested under these conditions. © 2009 Acta Materialia Inc.
    view abstract10.1016/j.scriptamat.2009.12.041
  • Easy synthesis of hollow polymer, carbon, and graphitized microspheres
    Lu, A.-H. and Li, W.-C. and Hao, G.-P. and Spliethoff, B. and Bongard, H.-J. and Schaack, B.B. and Schüth, F.
    Angewandte Chemie - International Edition 49 (2010)
    "Chemical Equation Presented" Balls galorel A new approach was developed for the easy synthesis of hollow microspheres with amorphous or graphitized microstructure. Starting from one type of solid polymer sphere, a simple water washing treatment led to the formation of hollow structures. Diverse products such as hollow carbon or graphitized spheres can be obtained, depending on subsequent treatment methods (see picture). © 2010 Wlley-VCH Verlag GmbH & Co. KGaA.
    view abstract10.1002/anie.200906445
  • Ex-post size control of high-temperature-stable yolk-shell Au,@ZrO 2 catalysts
    Güttel, R. and Paul, M. and Schüth, F.
    Chemical Communications 46 (2010)
    Yolk-shell catalysts have attracted interest in both academia and industry, since they combine high-temperature stability with a reduced complexity for kinetic and mechanistic investigations. This contribution presents a possibility to adjust the size of an active gold core inside a porous zirconia shell via an ex-post-modification approach. © The Royal Society of Chemistry 2010.
    view abstract10.1039/b921792d
  • From glycerol to allyl alcohol: Iron oxide catalyzed dehydration and consecutive hydrogen transfer
    Liu, Y. and Tüysüz, H. and Jia, C.-J. and Schwickardi, M. and Rinaldi, R. and Lu, A.-H. and Schmidt, W. and Schüth, F.
    Chemical Communications 46 (2010)
    Using iron oxide as catalyst, glycerol can be converted to allyl alcohol through a dehydration and consecutive hydrogen transfer. © 2010 The Royal Society of Chemistry.
    view abstract10.1039/b921648k
  • Growth of single-crystal mesoporous carbons with im 3̄ m symmetry
    Gu, D. and Bongard, H. and Meng, Y. and Miyasaka, K. and Terasaki, O. and Zhang, F. and Deng, Y. and Wu, Z. and Feng, D. and Fang, Y. and Tu, B. and Schüth, F. and Zhao, D.
    Chemistry of Materials 22 (2010)
    Highly ordered mesoporous carbon FDU-16 rhombic dodecahedral single crystals with body-centered cubic structure (space group Im3̄m) have been successfully synthesized by employing an organic-organic assembly of triblock copolymer Pluronic F127 (EO106PO70EO106) and phenol/formaldehyde resol in basic aqueous solution. Synthetic factors (including reaction time, temperature, and stirring rate) are explored for controlling the formation of rhombic dodecahedral single crystals. The optimal stirring rate and the reaction temperature are 300 ± 10 rpm and ∼66 °C, respectively. High-resolution scanning electron microscopy (HRSEM), scanning transmission electron microscopy (STEM), and ultramicrotomy are applied to study the fine structures of the carbon single crystals. The mesopores are arranged in body-centered cubic symmetry throughout the entire particle. Surface steps are clearly observed in the {110} surface, which suggests a layer-by-layer growth of the mesoporous carbon FDU-16 single crystals. Cryo-SEM results from the reactant solution confirm the formation of resol/F127 unit micelles, further supporting the layer-by-layer growth process. The mesoporous carbon FDU-16 single crystals grow up to the final size of 2-4 μm within 2 days. These findings may have consequences for the growth mechanism of other carbon materials in aqueous solution; moreover, the high-quality single crystals also have potential applications in nanodevice technologies. © 2010 American Chemical Society.
    view abstract10.1021/cm101648y
  • Highly active iron oxide supported gold catalysts for CO oxidation: How small must the gold nanoparticles be?
    Liu, Y. and Jia, C.-N. and Yamasaki, J. and Terasaki, O. and Schüth, F.
    Angewandte Chemie - International Edition 49 (2010)
    (Figure Presented) The shape of gold: The title catalyst has been prepared through a colloidal deposition method. Scanning transmission electron microscopy studies confirmed that for the catalyst, gold clusters with a bilayer structure and a diameter of about 0.5 nm are not mandatory to achieve the high activity (see image). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201000452
  • Influence of the ball milling conditions on the preparation of rare earth aluminum hydrides
    Pommerin, A. and Felderhoff, M. and Schüth, F. and Weidenthaler, C.
    Scripta Materialia 63 (2010)
    The ball milling conditions in the preparation of rare earth aluminum hydrides from NaAlH4 and rare earth chlorides have a significant influence on product formation. Defined milling times and appropriate rotational speeds are required to obtain the desired products. It has been shown that starting directly from Na3AlH6 does not lead to the formation of REAlH6. Starting from rare earth iodides instead of chlorides allows dissolution of the alkali metal iodide formed and, therewith, the preparation of salt-free rare earth aluminum hydrides. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.scriptamat.2010.08.020
  • Influence of the microstructure of gold-zirconia yolk-shell catalysts on the CO oxidation activity
    Pandey, A.D. and Güttel, R. and Leoni, M. and Schüth, F. and Weidenthaler, C.
    Journal of Physical Chemistry C 114 (2010)
    The gold-zirconia yolk-shell system is an interesting catalyst for CO oxidation. The size distribution of the gold nanoparticles is very narrow, and they are well separated from each other also after treatment at high temperature, which is due to their encapsulation in crystalline zirconia hollow spheres. Because this allows thermal and chemical treatment without affecting the size distribution, different defect structures of the gold nanoparticles can be induced, and the effect on catalytic activity can be investigated. Line profile analysis of the powder diffraction data based on the whole powder pattern modeling approach was used to determine the domain size distribution and lattice defects present in this two-phase system. The influence of different diffractometer setups on the results of the line profile analysis was also investigated. Variation of the chemical and thermal treatment procedures allowed altering the microstructure of the system. The resulting catalysts showed substantial variation in the activity for CO oxidation. Lower dislocation densities and less stacking faults result in decreased catalytic activity. These contributions to activity could be studied without any superimposed size effect due to the constant gold particle sizes. © 2010 American Chemical Society.
    view abstract10.1021/jp106436h
  • Kein Ausbau erneuerbarer Energien ohne chemische Technik
    Schüth, F. and Wagemann, K.
    Chemie-Ingenieur-Technik 82 (2010)
    view abstract10.1002/cite.201090012
  • One year for energy
    Schüth, F.
    Nachrichten aus der Chemie 58 (2010)
    view abstract10.1002/nadc.201070274
  • Overview of porous materials
    Schüth, F.
    Chemie-Ingenieur-Technik 82 (2010)
    view abstract10.1002/cite.201000063
  • Paving the way to new energy systems: The key role of the chemical sciences
    Schüth, F.
    ChemSusChem 3 (2010)
    view abstract10.1002/cssc.200900272
  • Regioselectively controlled synthesis of colloidal mushroom nanostructures and their hollow derivatives
    Feyen, M. and Weidenthaler, C. and Schüth, F. and Lu, A.-H.
    Journal of the American Chemical Society 132 (2010)
    In this study, a facile and controllable synthetic route for the fabrication of mushroom nanostructures (Fe xO y@PSD-SiO 2) and their hollow derivatives has been established. The synthesis consists of partial coating of Fe xO y (Fe 3O 4 or Fe 2O 3) with polymer spheres, followed by attaching silica hemispheres. The surface-accessible Fe xO y nanoparticles on the Janus-type Fe xO y@PSD nanospheres are key for directing the growth of the silica hemisphere on the Fe xO y@PSD seeds. The size and the porosity of the silica hemispheres are tunable by adjusting the amount of TEOS used and addition of a proper surfactant in a Stöber-type process. After the iron oxide cores were leached out with concentrated HCl, mushroom nanostructures with hollow interiors were obtained, where the morphology of the hollow interior faithfully replicates the shape of the iron oxide core previously filling this void. This synthetic strategy provides a controllable method for the large-scale preparation of asymmetric colloidal nanostructures which could serve as building blocks for the assembly of new types of nanostructures. © 2010 American Chemical Society.
    view abstract10.1021/ja101270r
  • Small gold particles supported on MgFe2O4 nanocrystals as novel catalyst for CO oxidation
    Jia, C.-J. and Liu, Y. and Schwickardi, M. and Weidenthaler, C. and Spliethoff, B. and Schmidt, W. and Schüth, F.
    Applied Catalysis A: General 386 (2010)
    We present the study on the catalytic performance of gold particles supported on spinel type MgFe2O4 nanocrystals (Au/MgFe2O4) which exhibit high activity for low temperature CO oxidation. Using XRD, TEM, XPS and CO titration techniques, we investigated the effect of the pretreatment atmosphere on the structure and catalytic properties of the Au/MgFe2O4 catalyst in CO oxidation. TEM, XPS and XRD showed that the pretreatment atmosphere had a negligible effect on the particle size distribution, chemical states of the gold, and the structure of the support. Among the various pretreated catalysts, O2-Au/MgFe2O4 exhibits superior activity, indicating that pretreatment in oxidative atmosphere induced the high capability of the catalyst to activate CO and supply active oxygen for CO oxidation as confirmed by CO titration experiments. © 2010 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.apcata.2010.07.036
  • Small-sized HZSM-5 zeolite as highly active catalyst for gas phase dehydration of glycerol to acrolein
    Jia, C.-J. and Liu, Y. and Schmidt, W. and Lu, A.-H. and Schüth, F.
    Journal of Catalysis 269 (2010)
    The catalytic properties of nanocrystalline HZSM-5 catalysts with high Si/Al molar ratio (ca. 65) were investigated in the gas phase dehydration of aqueous glycerol. Compared with bulk HZSM-5, the small-sized catalyst exhibits greatly enhanced catalytic performance in glycerol dehydration even with very high GHSV (=1438 h -1). Catalysts with different Si/Al ratios were studied, but it is difficult to separate the influence of Si/Al ratio from that of particle size. However, by varying the proton exchange degree for one mother batch of zeolite, a series of H xNa 1-xZSM-5 catalysts with same particle size and different Brønsted acid site densities was prepared. The catalytic results for this series of samples show that high density of Brønsted acid sites favors the production of acrolein. Based on these results, small-sized HZSM-5 with high aluminum content appears to be most promising for gas phase dehydration of glycerol. © 2009 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.jcat.2009.10.017
  • Spatially and size selective synthesis of Fe-based nanoparticles on ordered mesoporous supports as highly active and stable catalysts for ammonia decomposition
    Lu, A.-H. and Nitz, J.-J. and Comotti, M. and Weidenthaler, C. and Schlichte, K. and Lehmann, C.W. and Terasaki, O. and Schüth, F.
    Journal of the American Chemical Society 132 (2010)
    Uniform and highly dispersed γ-Fe 2O 3 nanoparticles with a diameter of ∼6 nm supported on CMK-5 carbons and C/SBA-15 composites were prepared via simple impregnation and thermal treatment. The nanostructures of these materials were characterized by XRD, Mössbauer spectroscopy, XPS, SEM, TEM, and nitrogen sorption. Due to the confinement effect of the mesoporous ordered matrices, γ-Fe 2O 3 nanoparticles were fully immobilized within the channels of the supports. Even at high Fe-loadings (up to about 12 wt %) on CMK-5 carbon no iron species were detected on the external surface of the carbon support by XPS analysis and electron microscopy. Fe 2O 3/CMK-5 showed the highest ammonia decomposition activity of all previously described Fe-based catalysts in this reaction. Complete ammonia decomposition was achieved at 700 °C and space velocities as high as 60 000 cm 3 g cat -1 h -1. At a space velocity of 7500 cm 3 g cat -1 h -1, complete ammonia conversion was maintained at 600 °C for 20 h. After the reaction, the immobilized γ-Fe 2O 3 nanoparticles were found to be converted to much smaller nanoparticles (γ-Fe 2O 3 and a small fraction of nitride), which were still embedded within the carbon matrix. The Fe 2O 3/CMK-5 catalyst is much more active than the benchmark NiO/Al 2O 3 catalyst at high space velocity, due to its highly developed mesoporosity. γ-Fe 2O 3 nanoparticles supported on carbon-silica composites are structurally much more stable over extended periods of time but less active than those supported on carbon. TEM observation reveals that iron-based nanoparticles penetrate through the carbon layer and then are anchored on the silica walls, thus preventing them from moving and sintering. In this way, the stability of the carbon-silica catalyst is improved. Comparison with the silica supported iron oxide catalyst reveals that the presence of a thin layer of carbon is essential for increased catalytic activity. © 2010 American Chemical Society.
    view abstract10.1021/ja105308e
  • Structure-Function Correlations for Ru/CNT in the Catalytic Decomposition of Ammonia
    Zheng, W. Q. and Zhang, J. and Zhu, B. and Blume, R. and Zhang, Y. L. and Schlichte, K. and Schlogl, R. and Schüth, F. and Su, D. S.
    Chemsuschem 3 (2010)
    view abstract10.1002/cssc.200900217
  • Substrate size-selective catalysis with zeolite-encapsulated gold nanoparticles
    Laursen, A.B. and Højholt, K.T. and Lundegaard, L.F. and Simonsen, S.B. and Helveg, S. and Schüth, F. and Paul, M. and Grunwaldt, J.-D. and Kegnœs, S. and Christensen, C.H. and Egeblad, K.
    Angewandte Chemie - International Edition 49 (2010)
    The Dark Crystal: A hybrid material is reported that is comprised of 1-2 nm sized gold nanoparticles, accessible only through zeolite micropores in a silicalite-1 crystal, as shown by three-dimensional TEM tomography (see picture). Calcination experiments indicate that the embedded nanoparticles are highly stable towards sintering. Figure Equation Present. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstract10.1002/anie.200906977
  • Support effects in the Au-catalyzed CO oxidation - Correlation between activity, oxygen storage capacity, and support reducibility
    Widmann, D. and Liu, Y. and Schüth, F. and Behm, R.J.
    Journal of Catalysis 276 (2010)
    The oxygen storage capacity (OSC) and its correlation with the activity for the CO oxidation reaction and the reducibility of the support material were investigated for four different metal oxide-supported Au catalysts with similar Au loading and Au particle sizes (Au/Al2O3, Au/TiO 2, Au/ZnO, Au/ZrO2), which were prepared by deposition of pre-formed Au colloids. Temporal Analysis of Products (TAP) reactor measurements show that the OSC and the activity for CO oxidation, measured under identical conditions, differ significantly for these catalysts and are correlated with each other and with the reducibility of the respective support material, pointing to a distinct support effect and a direct participation of the support in the reaction. Activity measurements performed under ambient conditions show a similar trend of the activity as the TAP reactor measurements, supporting that the conclusions drawn from the TAP reactor measurements are valid also under continuous reaction conditions. Moreover, the rapid formation and accumulation of carbon-containing surface species during reaction is demonstrated, which can severely reduce the activity for CO oxidation. Implications of these results on the CO oxidation mechanism over metal oxide-supported catalysts are discussed. © 2010 Elsevier Inc. All rights reserved.
    view abstract10.1016/j.jcat.2010.09.023
  • Synthesis of structurally stable colloidal composites as magnetically recyclable acid catalysts
    Feyen, M. and Weidenthaler, C. and Schüth, F. and Lu, A.-H.
    Chemistry of Materials 22 (2010)
    In this study, we provide a simple and reproducible method for the preparation of highly active and recyclable colloidal acid catalysts. First, 16-heptadecenoic acid-functionalized magnetite nanoparticles were encapsulated in monodisperse cross-linked polymer spheres. This was achieved by emulsion copolymerization technique in an aqueous phase of styrene and divinylbenzene (DVB). Different ratios of styrene and DVB were used to tune the structural stability and surface morphology of the composites. With increase in DVB content, the surfaces of the colloidal composites become increasingly rougher. The obtained colloids were functionalized with sulfonic acid groups to obtain magnetically recyclable catalysts with H+ contents in the range of 2.2-2.5 mmol g-1 and surface areas of 45-120 m2 g -1. For the condensation reaction of benzaldehyde and ethylene glycol, magnetic acid catalyst prepared only from DVB precursor was found to be active and with high selectivity and long-term stability. © 2010 American Chemical Society.
    view abstract10.1021/cm100277k
  • Very low temperature CO oxidation over colloidally deposited gold nanoparticles on Mg(OH)2 and MgO
    Jia, C.-N. and Liu, Y. and Bongard, H. and Schüth, F.
    Journal of the American Chemical Society 132 (2010)
    (Figure Presented) The colloidal deposition method was used to prepare Au/Mg(OH)2 (0.7 wt % gold) catalysts with gold particle sizes between 1.5 to 5 nm which exhibited very high activity for CO oxidation with specific rates higher than 3.7 molCO·h-1·g Au-1 even at temperatures as low as -89° C. © 2010 American Chemical Society.
    view abstract10.1021/ja909351e
  • Which controls the depolymerization of cellulose in ionic liquids: The solid acid catalyst or cellulose?
    Rinaldi, R. and Meine, N. and vom Stein, J. and Palkovits, R. and Schüth, F.
    ChemSusChem 3 (2010)
    Cellulose is a renewable and widely available feedstock. It is a biopolymer that is typically found in wood, straw, grass, municipal solid waste, and crop residues. Its use as raw material for biofuel production opens up the possibility of sustainable biorefinery schemes that do not compete with food supply. Tapping into this feedstock for the production of biofuels and chemicals requires-as the first-step-its depolymerization or its hydrolysis into intermediates that are more susceptible to chemical and/or biological transformations. We have shown earlier that solid acids selectively catalyze the depolymerization of cellulose solubilized in 1-butyl-3-methylimidazolium chloride (BMIMCl) at 100°C. Here, we address the factors responsible for the control of this reaction. Both cellulose and solid acid catalysts have distinct and important roles in the process. Describing the depolymerization of cellulose by the equivalent number of scissions occurring in the cellulosic chains allows a direct correlation between the product yields and the extent of the polymer breakdown. The effect of the acid strength on the depolymerization of cellulose is discussed in detail. Practical aspects of the reaction, concerning the homogeneous nature of the catalysis in spite of the use of a solid acid catalyst, are thoroughly addressed. The effect of impurities present in the imidazolium-based ionic liquids on the reaction performance, the suitability of different ionic liquids as solvents, and the recyclability of Amberlyst 15DRY and BMIMCl are also presented. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cssc.200900281
  • biomass conversion

  • catalysis

  • heterogeneous catalysis

  • hydrogen storage

  • mesoporous materials

  • porous nanostructures

  • synthesis

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