Dr. Claudia Weidenthaler
Max-Planck-Institut für Kohlenforschung
- Correlating the Synthesis, Structure, and Catalytic Performance of Pt-Re/TiO2for the Aqueous-Phase Hydrogenation of Carboxylic Acid Derivatives
Haus, M.O. and Meledin, A. and Leiting, S. and Louven, Y. and Roubicek, N.C. and Moos, S. and Weidenthaler, C. and Weirich, T.E. and Palkovits, R.
ACS Catalysis 11 (2021)Pt-Re bimetallic catalysts have many applications, ranging from catalytic reforming to the reduction of carboxylic acid derivatives. However, the exact role of Re in these systems has remained a matter of discussion, partly due to the plethora of suggested synthesis protocols and analysis conditions. This study presents an extensive comparison of such literature protocols and the resulting materials. In detail, characterization by N2 physisorption, X-ray diffraction, temperature-programmed reduction, CO pulse chemisorption, Fourier-transform infrared spectroscopy of adsorbed CO, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and in situ X-ray photoelectron spectroscopy is combined with catalytic testing to yield synthesis-structure-activity correlations. Accordingly, the investigated catalysts share common features, such as Pt0 nanoparticles (1-4 nm) decorated with partially reduced Re species (ReOx-y). The remaining rhenium oxide is spread over the TiO2 support and enhances Pt dispersion in sequential impregnation protocols. While differences in the number of active sites (Pt0/ReOx-y) mostly explain catalytic results, small variations in the extent of Re reduction and site composition cause additional modulations. The optimal bimetallic catalyst outperforms Ru/C (previous benchmark) in the reduction of N-(2-hydroxyethyl)succinimide, an important step in the production of a bio-based polyvinylpyrrolidone polymer. © 2021 American Chemical Society. All rights reserved.
view abstract 10.1021/acscatal.0c05612
- Identification of Active Sites in the Catalytic Oxidation of 2-Propanol over Co1+xFe2–xO4 Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces
Falk, T. and Budiyanto, E. and Dreyer, M. and Pflieger, C. and Waffel, D. and Büker, J. and Weidenthaler, C. and Ortega, K.F. and Behrens, M. and Tüysüz, H. and Muhler, M. and Peng, B.
ChemCatChem 13 (2021)A series of Co1+xFe2–xO4 (0≤x≤2) spinel nanowires was synthesized by nanocasting using SBA-15 silica as hard template, which was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The Co1+xFe2–xO4 spinels were applied in the aerobic oxidation of aqueous 2-propanol solutions to systematically study the influence of exposed Co and Fe cations on the catalytic properties. The activity of the catalysts was found to depend strongly on the Co content, showing an exponential increase of the reaction rate with increasing Co content. Ensembles of Co3+cus (coordinatively unsaturated) sites were identified as the active sites for selective 2-propanol oxidation, which are assumed to consist of more than six Co ions. In addition, gas-phase oxidation with and without water vapor co-feeding was performed to achieve a comparison with liquid-phase oxidation kinetics. An apparent activation energy of 94 kJ mol−1 was determined for 2-propanol oxidation over Co3O4 in the liquid phase, which is in good agreement with the gas-phase oxidation in the presence of water vapor. In contrast to gas-phase conditions, the catalysts showed high stability and reusability in the aqueous phase with constant conversion in three consecutive runs. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH
view abstract 10.1002/cctc.202100352
- In Situ Synchrotron X-ray Diffraction Studies of the Mechanochemical Synthesis of ZnS from its Elements
Petersen, H. and Reichle, S. and Leiting, S. and Losch, P. and Kersten, W. and Rathmann, T. and Tseng, J. and Etter, M. and Schmidt, W. and Weidenthaler, C.
Chemistry - A European Journal (2021)Mechanochemistry, as a synthesis tool for inorganic materials, became an ever-growing field in material chemistry. The direct energy transfer by collision of the educts with the milling media gives the possibility to design environmental-friendly reactions. Nevertheless, the underlying process of energy transfer and hence the kinetics of mechanosynthesis remain unclear. Herein, we present in situ synchrotron X-ray diffraction studies coupled with pressure measurements performed during the formation of ZnS and the subsequent phase transition (PT) from the hexagonal to the cubic modification. Milling Zn and S8 results in the sublimation of S8, observed by a sudden pressure increase. Simultaneously, the hexagonal metastable ZnS-modification (wurtzite) forms. Via detection of the pressure maximum, the exact start of the wurtzite formation can be determined. Immediately after the formation of wurtzite, the structural PT to the thermodynamic stable cubic modification sphalerite takes place. This PT can be described by the Prout-Tompkins equation for autocatalytic reactions, similar to thermally induced PT in sulfur vapor at high temperatures (T>1133 K). The increase in the reactivity of the wurtzite formation is explained by the reaction in sulfur vapor and the induction of defect structures by the collisions with the milling media. © 2021 The Authors. Published by Wiley-VCH GmbH
view abstract 10.1002/chem.202101260
- In situ total scattering experiments of nucleation and crystallisation of tantalum-based oxides: From highly dilute solutions via cluster formation to nanoparticles
Onur Şahin, E. and Tüysüz, H. and Chan, C.K. and Moon, G.-H. and Dai, Y. and Schmidt, W. and Lim, J. and Scheu, C. and Weidenthaler, C.
Nanoscale 13 (2021)The exact formation mechanism of tantalum oxides (and in general, metal/mixed metal oxides) from alkoxide precursors is still not fully understood, particularly when forming cluster-like or amorphous materials. The structural evolution of Ta-based oxides was studied in detail using X-ray total scattering experiments along with subsequent pair distribution function (PDF) analyses. Starting from a tantalum alkoxide precursor (Ta2(OEt)10), the formation of hydrolysed TaxOyHz clusters in highly diluted aqueous solution was analysed. From the PDF data, the connectivity and arrangement of TaxOy octahedra in the cluster could be deduced as well as the approximate size of the clusters (<1 nm). Construction of cluster models allowed for identification of common structural motifs in the TaxOyHz clusters, ruling out the formation of chain- or ring-like clusters. More likely, bulky clusters with a high number of corner-sharing octahedra are formed. After separation of the amorphous solid from the liquid, temperature-induced crystallisation processes were monitored via in situ total scattering experiments. Between room temperature and 600 °C, only small rearrangements of the amorphous structure are observed. At about 610 °C, amorphous TaxOyHz transforms directly into crystalline orthorhombic L-Ta2O5 without formation of any crystalline intermediate structures. © 2021 The Royal Society of Chemistry.
view abstract 10.1039/d0nr07871a
- Metal-Ligand Interface and Internal Structure of Ultrasmall Silver Nanoparticles (2 nm)
Wetzel, O. and Hosseini, S. and Loza, K. and Heggen, M. and Prymak, O. and Bayer, P. and Beuck, C. and Schaller, T. and Niemeyer, F. and Weidenthaler, C. and Epple, M.
Journal of Physical Chemistry B 125 (2021)Ultrasmall silver nanoparticles were prepared by reduction with NaBH4 and surface-terminated with glutathione (GSH). The particles had a solid core diameter of 2 nm as shown by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). NMR-DOSY gave a hydrodynamic diameter of 2 to 2.8 nm. X-ray photoelectron spectroscopy (XPS) showed that silver is bound to the thiol group of the central cysteine in glutathione under partial oxidation to silver(+I). In turn, the thiol group is deprotonated to thiolate. X-ray powder diffraction (XRD) together with Rietveld refinement confirmed a twinned (polycrystalline) fcc structure of ultrasmall silver nanoparticles with a lattice compression of about 0.9% compared to bulk silver metal. By NMR spectroscopy, the interaction between the glutathione ligand and the silver surface was analyzed, also with 13C-labeled glutathione. The adsorbed glutathione is fully intact and binds to the silver surface via cysteine. In situ 1H NMR spectroscopy up to 85 °C in dispersion showed that the glutathione ligand did not detach from the surface of the silver nanoparticle, i.e. the silver-sulfur bond is remarkably strong. The ultrasmall nanoparticles had a higher cytotoxicity than bigger particles in in vitro cell culture with HeLa cells with a cytotoxic concentration of about 1 μg mL-1 after 24 h incubation. The overall stoichiometry of the nanoparticles was about Ag∼250GSH∼155. © 2021 The Authors. Published by American Chemical Society.
view abstract 10.1021/acs.jpcb.1c02512
- Monitoring the Structure Evolution of Titanium Oxide Photocatalysts: From the Molecular Form via the Amorphous State to the Crystalline Phase
Onur Şahin, E. and Dai, Y. and Chan, C.K. and Tüysüz, H. and Schmidt, W. and Lim, J. and Zhang, S. and Scheu, C. and Weidenthaler, C.
Chemistry - A European Journal (2021)Amorphous TixOy with high surface area has attracted significant interest as photocatalyst with higher activity in ultraviolet (UV) light-induced water splitting applications compared to commercial nanocrystalline TiO2. Under photocatalytic operation conditions, the structure of the molecular titanium alkoxide precursor rearranges upon hydrolysis and leads to higher connectivity of the structure-building units. Structurally ordered domains with sizes smaller than 7 Å form larger aggregates. The experimental scattering data can be explained best with a structure model consisting of an anatase-like core and a distorted shell. Upon exposure to UV light, the white TixOy suspension turns dark corresponding to the reduction of Ti4+ to Ti3+ as confirmed by electron energy loss spectroscopy (EELS). Heat-induced crystallisation was followed by in situ temperature-dependent total scattering experiments. First, ordering in the Ti−O environment takes place upon to 350 °C. Above this temperature, the distorted anatase core starts to grow but the structure obtained at 400 °C is still not fully ordered. © 2021 The Authors. Published by Wiley-VCH GmbH
view abstract 10.1002/chem.202101117
- 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 abstract 10.1039/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 abstract 10.1149/1945-7111/abd830
- Crystal structure evolution of complex metal aluminum hydrides upon hydrogen release
Journal of Energy Chemistry 42 (2020)Complex aluminum hydrides have been widely studied as potential hydrogen storage materials but also, for some time now, for electrochemical applications. This review summarizes the crystal structures of alkali and alkaline earth aluminum hydrides and correlates structure properties with physical and chemical properties of the hydride compounds. The crystal structures of the alkali metal aluminum hydrides change significantly during the stepwise dehydrogenation. The general pathway follows a transformation of structures built of isolated [AlH4]− tetrahedra to structures built of isolated [AlH6]3− octahedra. The crystal structure relations in the group of alkaline earth metal aluminum hydrides are much more complicated than those of the alkali metal aluminum hydrides. The structures of the alkaline earth metal aluminum hydrides consist of isolated tetrahedra but the intermediate structures exhibit chains of corner-shared octahedra. The coordination numbers within the alkali metal group increase with cation sizes which goes along with an increase of the decomposition temperatures of the primary hydrides. Alkaline earth metal hydrides have higher coordination numbers but decompose at slightly lower temperatures than their alkali metal counterparts. The decomposition pathways of alkaline metal aluminum hydrides have not been studied in all cases and require future research. © 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences
view abstract 10.1016/j.jechem.2019.05.026
- Dual Role of Silver Moieties Coupled with Ordered Mesoporous Cobalt Oxide towards Electrocatalytic Oxygen Evolution Reaction
Yu, M. and Moon, G.-H. and Castillo, R.G. and DeBeer, S. and Weidenthaler, C. and Tüysüz, H.
Angewandte Chemie - International Edition 59 (2020)Herein, we show that the performance of mesostructured cobalt oxide electrocatalyst for oxygen evolution reaction (OER) can be significantly enhanced by coupling of silver species. Various analysis techniques including pair distribution function and Rietveld refinement, X-ray absorption spectroscopy at synchrotron as well as advanced electron microscopy revealed that silver exists as metallic Ag particles and well-dispersed Ag2O nanoclusters within the mesostructure. The benefits of this synergy are twofold for OER: highly conductive metallic Ag improves the charge transfer ability of the electrocatalysts while ultra-small Ag2O clusters provide the centers that can uptake Fe impurities from KOH electrolyte and boost the catalytic efficiency of Co–Ag oxides. The current density of mesostructured Co3O4 at 1.7 VRHE is increased from 102 to 211 mA cm−2 with incorporation of silver spices. This work presents the dual role of silver moieties and demonstrates a simple method to increase the OER activity of Co3O4. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
view abstract 10.1002/anie.202003801
- 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 abstract 10.1016/j.micromeso.2020.110566
- Laser Fragmentation-Induced Defect-Rich Cobalt Oxide Nanoparticles for Electrochemical Oxygen Evolution Reaction
Yu, M. and Waag, F. and Chan, C.K. and Weidenthaler, C. and Barcikowski, S. and Tüysüz, H.
ChemSusChem 13 (2020)Sub-5 nm cobalt oxide nanoparticles are produced in a flowing water system by pulsed laser fragmentation in liquid (PLFL). Particle fragmentation from 8 nm to 4 nm occurs and is attributed to the oxidation process in water where oxidative species are present and the local temperature is rapidly elevated under laser irradiation. Significantly higher surface area, crystal phase transformation, and formation of structural defects (Co2+ defects and oxygen vacancies) through the PLFL process are evidenced by detailed structural characterizations by nitrogen physisorption, electron microscopy, synchrotron X-ray diffraction, and X-ray photoelectron spectroscopy. When employed as electrocatalysts for the oxygen evolution reaction under alkaline conditions, the fragmented cobalt oxides exhibit superior catalytic activity over pristine and nanocast cobalt oxides, delivering a current density of 10 mA cm−2 at 369 mV and a Tafel slope of 46 mV dec−1, which is attributed to a larger exposed active surface area, the formation of defects, and an increased charge transfer rate. The study provides an effective approach to engineering cobalt oxide nanostructures in a flowing water system, which shows great potential for sustainable production of active cobalt catalysts. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/cssc.201903186
- Materials for hydrogen-based energy storage – past, recent progress and future outlook
Hirscher, M. and Yartys, V.A. and Baricco, M. and Bellosta von Colbe, J. and Blanchard, D. and Bowman, R.C., Jr. and Broom, D.P. and Buckley, C.E. and Chang, F. and Chen, P. and Cho, Y.W. and Crivello, J.-C. and Cuevas, F. and David, W.I.F. and de Jongh, P.E. and Denys, R.V. and Dornheim, M. and Felderhoff, M. and Filinchuk, Y. and Froudakis, G.E. and Grant, D.M. and Gray, E.M. and Hauback, B.C. and He, T. and Humphries, T.D. and Jensen, T.R. and Kim, S. and Kojima, Y. and Latroche, M. and Li, H.-W. and Lototskyy, M.V. and Makepeace, J.W. and Møller, K.T. and Naheed, L. and Ngene, P. and Noréus, D. and Nygård, M.M. and Orimo, S.-I. and Paskevicius, M. and Pasquini, L. and Ravnsbæk, D.B. and Veronica Sofianos, M. and Udovic, T.J. and Vegge, T. and Walker, G.S. and Webb, C.J. and Weidenthaler, C. and Zlotea, C.
Journal of Alloys and Compounds 827 (2020)Globally, the accelerating use of renewable energy sources, enabled by increased efficiencies and reduced costs, and driven by the need to mitigate the effects of climate change, has significantly increased research in the areas of renewable energy production, storage, distribution and end-use. Central to this discussion is the use of hydrogen, as a clean, efficient energy vector for energy storage. This review, by experts of Task 32, “Hydrogen-based Energy Storage” of the International Energy Agency, Hydrogen TCP, reports on the development over the last 6 years of hydrogen storage materials, methods and techniques, including electrochemical and thermal storage systems. An overview is given on the background to the various methods, the current state of development and the future prospects. The following areas are covered; porous materials, liquid hydrogen carriers, complex hydrides, intermetallic hydrides, electrochemical storage of energy, thermal energy storage, hydrogen energy systems and an outlook is presented for future prospects and research on hydrogen-based energy storage. © 2020 The Authors
view abstract 10.1016/j.jallcom.2019.153548
- Nanocast Mixed Ni-Co-Mn Oxides with Controlled Surface and Pore Structure for Electrochemical Oxygen Evolution Reaction
Priamushko, T. and Guillet-Nicolas, R. and Yu, M. and Doyle, M. and Weidenthaler, C. and Tuÿsüz, H. and Kleitz, F.
ACS Applied Energy Materials 3 (2020)Nanocasting or hard-templating is a versatile method to produce ordered mesoporous mixed transition metal oxides (MTMOs) with promising potential for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a comprehensive investigation was conducted on various NixCoyMnzO4 replicated from large pore KIT-6 silica. The materials were calcined at different temperatures to study the influence of the oxide formation and the resulting pore structure ordering, as well as surface properties, on the electrochemical activity and stability of the catalysts. After a comprehensive characterization, electrocatalytic performances of the materials were investigated in detail for OER to find a structure-activity relationship. In OER, a correlation was established between calcination temperature, pore and surface properties, and the overall efficiency and stability. The best sample, NixCoyMnzO4 calcined at 300 °C, provided a reasonable current density (25 mA/cm2 at 1.7 V vs RHE) and an overpotential of 400 mV at 10 mA/cm2, and demonstrated increased current density (above 200 mA/cm2 at 1.7 V vs RHE) once loaded into a Ni foam compared to the bare foam. This sample also remained stable over 15 h. Our results indicate that the calcination temperature greatly affects the porosity, crystalline structure, phase composition, and the activity of the catalysts toward OER. Copyright © 2020 American Chemical Society.
view abstract 10.1021/acsaem.0c00544
- One-Pot Cooperation of Single-Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization-Hydrosilylation Process
Sarma, B.B. and Kim, J. and Amsler, J. and Agostini, G. and Weidenthaler, C. and Pfänder, N. and Arenal, R. and Concepción, P. and Plessow, P. and Studt, F. and Prieto, G.
Angewandte Chemie - International Edition 59 (2020)Realizing the full potential of oxide-supported single-atom metal catalysts (SACs) is key to successfully bridge the gap between the fields of homogeneous and heterogeneous catalysis. Here we show that the one-pot combination of Ru1/CeO2 and Rh1/CeO2 SACs enables a highly selective olefin isomerization-hydrosilylation tandem process, hitherto restricted to molecular catalysts in solution. Individually, monoatomic Ru and Rh sites show a remarkable reaction specificity for olefin double-bond migration and anti-Markovnikov α-olefin hydrosilylation, respectively. First-principles DFT calculations ascribe such selectivity to differences in the binding strength of the olefin substrate to the monoatomic metal centers. The single-pot cooperation of the two SACs allows the production of terminal organosilane compounds with high regio-selectivity (>95 %) even from industrially-relevant complex mixtures of terminal and internal olefins, alongside a straightforward catalyst recycling and reuse. These results demonstrate the significance of oxide-supported single-atom metal catalysts in tandem catalytic reactions, which are central for the intensification of chemical processes. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/anie.201915255
- 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 abstract 10.1126/science.abb0948
- Selective Hydrogenation of Benzofurans Using Ruthenium Nanoparticles in Lewis Acid-Modified Ruthenium-Supported Ionic Liquid Phases
El Sayed, S. and Bordet, A. and Weidenthaler, C. and Hetaba, W. and Luska, K.L. and Leitner, W.
ACS Catalysis 10 (2020)Ruthenium nanoparticles immobilized on a Lewis-acid-functionalized supported ionic liquid phase (Ru@SILP-LA) act as effective catalysts for the selective hydrogenation of benzofuran derivatives to dihydrobenzofurans. The individual components (nanoparticles, chlorozincate-based Lewis-acid, ionic liquid, support) of the catalytic system are assembled using a molecular approach to bring metal and acid sites in close contact on the support material, allowing the hydrogenation of O-containing heteroaromatic rings while keeping the aromaticity of C6-rings intact. The chlorozincate species were identified to be predominantly [ZnCl4]2- anions using X-ray photoelectron spectroscopy and are in close interaction with the metal nanoparticles. The Ru@SILP-[ZnCl4]2- catalyst exhibited high activity, selectivity, and stability for the catalytic hydrogenation of a variety of substituted benzofurans, providing easy access to biologically relevant dihydrobenzofuran motifs under continuous flow conditions. Copyright © 2020 American Chemical Society.
view abstract 10.1021/acscatal.9b05124
- 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 abstract 10.1126/science.aaw9377
- Reversible ammonia-based and liquid organic hydrogen carriers for high-density hydrogen storage: Recent progress
Makepeace, J.W. and He, T. and Weidenthaler, C. and Jensen, T.R. and Chang, F. and Vegge, T. and Ngene, P. and Kojima, Y. and de Jongh, P.E. and Chen, P. and David, W.I.F.
International Journal of Hydrogen Energy 44 (2019)Liquid hydrogen carriers are considered to be attractive hydrogen storage options because of their ease of integration into existing chemical transportation infrastructures when compared with liquid or compressed hydrogen. The development of such carriers forms part of the work of the International Energy Agency Task 32: Hydrogen-Based Energy Storage. Here, we report the state-of-the-art for ammonia-based and liquid organic hydrogen carriers, with a particular focus on the challenge of ensuring easily regenerable, high-density hydrogen storage. © 2019 The Authors
view abstract 10.1016/j.ijhydene.2019.01.144
- Low Temperature Formation of Ruddlesden–Popper-Type Layered La2CoO4 ±δ Perovskite Monitored via In Situ X-ray Powder Diffraction
Ortatatlı, Ş. and Ternieden, J. and Weidenthaler, C.
European Journal of Inorganic Chemistry 2018 (2018)In this contribution low temperature formation of Ruddlesden–Popper (RP)-type layered La2CoO4±δ perovskite was optimized via in situ X-ray powder diffraction (XRPD). Starting from LaCoO3 a stoichiometric transformation to La2CoO4±δ and CoO can be achieved by controlled reduction with H2. The challenge of this reaction is the use of appropriate amounts of H2 in a defined temperature region. If the amount of H2 is too high, complete reduction of the perovskite occurs. If temperatures are not appropriate, intermediate phases seem to hinder the transformation to La2CoO4±δ or lead to a complete decomposition to simple oxides. Based on in situ XRPD experiments, the temperature window and required amount of H2 for the transformation of LaCoO3 to La2CoO4±δ were determined. Systematic experiments reveal that 650 °C is the optimal temperature for the complete transformation of LaCoO3 into La2CoO4±δ and CoO/Co0. The information was then transferred to realize bulk synthesis of La2CoO4±δ at 650 °C in a tube furnace without extended heat treatments at elevated temperatures. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/ejic.201801162
- 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 abstract 10.1039/c7cp07840d
- Promoting effect of solvent on Cu/CoO catalyst for selective glycerol oxidation under alkaline conditions
Dodekatos, G. and Ternieden, J. and Schünemann, S. and Weidenthaler, C. and Tüysüz, H.
Catalysis Science and Technology 8 (2018)Cu/CoO catalysts were employed for the selective oxidation of glycerol in the aqueous phase under basic conditions. The effect of the solvent on the catalytic performance was investigated and the impact on the catalyst was thoroughly elucidated. Detailed characterization of the catalysts by HR-TEM, XRD, and XPS analysis before and after the reaction revealed that the addition of co-solvents (ethanol, n-propanol, or tert-butanol) drastically altered the catalyst properties. In particular, the amount of the catalytically active CoO(OH) phase generated during the reaction depends on the co-solvent used. Generally, the co-solvent has a beneficial effect on the catalytic activity and improves the glycerol conversion by a factor of up to 1.8, which could be linearly correlated to the ET(30) solvent polarity. © 2018 The Royal Society of Chemistry.
view abstract 10.1039/c8cy01284a
- Selective production of glycols from xylitol over Ru on covalent triazine frameworks-suppressing decarbonylation reactions
Beine, A.K. and Krüger, A.J.D. and Artz, J. and Weidenthaler, C. and Glotzbach, C. and Hausoul, P.J.C. and Palkovits, R.
Green Chemistry 20 (2018)Ru on covaltent triazine frameworks (CTF) are highly active and selective catalysts for the conversion of xylitol to glycols (80% C-yield) in basic media. With increasing N-content decarbonylation reactions are suppressed leading to high glycol selectivity. The suppression can be attributed to the presence of N in the support and to metal-support interactions. The catalysts exhibit high stability and could be recycled 5 times with minor loss of activity. © The Royal Society of Chemistry 2018.
view abstract 10.1039/c8gc00208h
- Synthesis, crystal structure analysis and decomposition of RbALH44
Weidenthaler, C. and Felderhoff, M. and Bernert, T. and Sørby, M.H. and Hauback, B.C. and Krech, D.
Crystals 8 (2018)RbAlH44, a member of the complex metal aluminum hydride family, can be synthesized phase pure by different synthesis routes. Synthesis from the metals by a mechanochemical reaction requires the presence of a catalyst, but also emphasizes the reversibility of hydrogenation. The structure refinement of neutron diffraction data confirms that RbAlD44 is isostructural to KAlD44. The decomposition proceeds via two distinct processes at temperatures above 275 °C. However, the structures formed during decomposition seem to be different from the compounds formed during hydrogen release of early alkali metal aluminum hydrides. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
view abstract 10.3390/cryst8020103
- Tracking the Active Catalyst for Iron-Based Ammonia Decomposition by In Situ Synchrotron Diffraction Studies
Tseng, J.-C. and Gu, D. and Pistidda, C. and Horstmann, C. and Dornheim, M. and Ternieden, J. and Weidenthaler, C.
ChemCatChem 10 (2018)Iron-based catalysts for NH3 decomposition have been studied by a combination of catalytic tests and in situ synchrotron diffraction experiments performed in an inert sapphire plug-flow cell. In contrast to steel-based reaction cells, sapphire or quartz glass cells show no blind activity. Starting from iron oxide precursors, iron nitrides form during the activation cycle. Nitrides remain as main crystalline phases and govern the conversion of NH3 decomposition in the subsequent cycles. In this work structural and compositional changes of the nitrides were monitored in situ during heating and cooling cycles. The state of the catalyst under reaction conditions was analyzed by high resolution in situ synchrotron diffraction experiments. The analyses enable establishing reaction pathways and correlation of structural features with catalytic conversions. The most active phases are iron nitrides with high mobility and solubility for nitrogen atoms, such as Fe3Nx. Phase changes from Fe3Nx to γ-FeNx were observed above 700 °C. The formation of γ-FeNx seems to suppress the catalytic conversion. Moreover, the positive influence of a mesostructured support/catalyst composite on the catalytic conversion and catalyst stability were studied in detail. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/cctc.201800398
- Iron-Induced Activation of Ordered Mesoporous Nickel Cobalt Oxide Electrocatalyst for the Oxygen Evolution Reaction
Deng, X. and Öztürk, S. and Weidenthaler, C. and Tüysüz, H.
ACS Applied Materials and Interfaces 9 (2017)Herein, ordered mesoporous nickel cobalt oxides prepared by the nanocasting route are reported as highly active oxygen evolution reaction (OER) catalysts. By using the ordered mesoporous structure as a model system and afterward elevating the optimal catalysts composition, it is shown that, with a simple electrochemical activation step, the performance of nickel cobalt oxide can be significantly enhanced. The electrochemical impedance spectroscopy results indicated that charge transfer resistance increases for Co3O4 spinel after an activation process, while this value drops for NiO and especially for CoNi mixed oxide significantly, which confirms the improvement of oxygen evolution kinetics. The catalyst with the optimal composition (Co/Ni 4/1) reaches a current density of 10 mA/cm2 with an overpotential of a mere 336 mV and a Tafel slope of 36 mV/dec, outperforming benchmarked and other reported Ni/Co-based OER electrocatalysts. The catalyst also demonstrates outstanding durability for 14 h and maintained the ordered mesoporous structure. The cyclic voltammograms along with the electrochemical measurements in Fe-free KOH electrolyte suggest that the activity boost is attributed to the generation of surface Ni(OH)2 species that incorporate Fe impurities from the electrolyte. The incorporation of Fe into the structure is also confirmed by inductively coupled plasma optical emission spectrometry. © 2017 American Chemical Society.
view abstract 10.1021/acsami.7b02571
- Monodispersed Mesoporous Silica Spheres Supported Co3O4 as Robust Catalyst for Oxygen Evolution Reaction
Deng, X. and Rin, R. and Tseng, J.-C. and Weidenthaler, C. and Apfel, U.-P. and Tüysüz, H.
ChemCatChem 9 (2017)Monodispersed mesoporous silica spheres (MSS) with fibrous nanostructure and highly open porosity were fabricated by a facile one-pot synthetic route and loaded with Co3O4 nanoclusters for catalyzing the oxygen evolution reaction with Ru(bpy)3 2+–S2O8 2− photosensitizer and sacrificial reagent system. The effect of the loading amount on the morphology and microstructure of Co3O4 was investigated and it was found that lower Co3O4 content in the composite materials results in smaller crystallite size, which in turn leads to significantly enhanced oxygen evolution activity. Furthermore, owing to the monodispersity of the spheres and good accessibility of active species offered by the fibrous pore structure, the material shows a clear advantage over nonsupported Co3O4 nanoparticles and the commonly used ordered mesoporous silica supports such as KIT-6 and SBA-15. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/cctc.201701001
- Role of Dissolved and Molecular Oxygen on Cu and PtCu Alloy Particle Structure during Laser Ablation Synthesis in Liquids
Marzun, G. and Bönnemann, H. and Lehmann, C. and Spliethoff, B. and Weidenthaler, C. and Barcikowski, S.
ChemPhysChem 18 (2017)The role of molecular oxygen dissolved in the solvent is often discussed as being an influential factor on particle oxidation during pulsed laser ablation in liquids. However, the formation of the particles during laser synthesis takes place under extreme conditions that enable the decomposition of the liquid medium. Reactive species of the solvent may then affect particle formation due to a chemical reaction in the reactive plasma. Experimental results show a difference between the role of dissolved molecular oxygen and the contribution from the oxygen in water molecules. Using a metallic Cu target in air-saturated water, laser ablation led to 20.5 wt % Cu, 11.5 wt % Cu2O, and 68 wt % CuO nanoparticles, according to X-ray diffraction results. In contrast to particles obtained in air-saturated water, no CuO was observed in the colloid synthesized in a Schlenk ablation chamber in completely oxygen-free water. Under these conditions, less-oxidized nanoparticles (25 wt % Cu and 75 wt % Cu2O) were synthesized. The results show that nanoparticle oxidation during laser synthesis is mainly caused by reactive oxygen species from the decomposition of water molecules. However, the addition of molecular oxygen promotes particle oxidation. Storage of the Cu colloid in the presence of dissolved oxygen leads, due to aging, to nanostructures with a higher oxidation state than the freshly prepared colloid. The XRD pattern of the sample prepared in air-saturated acetone showed no crystalline phases, which is possibly due to small crystallites or low particle concentration. Concentration of the particles by centrifugation showed that in the large fraction (>20 nm), even less oxidized nanoparticles (46 wt % Cu and 54 wt % Cu2O) were present, although the solubility of molecular oxygen is higher in acetone than in water. The nanoparticles in acetone were stable due to a Cu-catalyzed graphite layer formed on their surfaces. The influence of the solvent on alloy synthesis is also crucial. Laser ablation of PtCu3 in air-saturated water led to separated large CuO and Pt-rich spherical nanoparticles, whereas homogeneous PtCu3 alloy nanoparticles were formed in acetone. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/cphc.201601315
- The roles of Co-precipitation pH, phase-purity and alloy formation for the ammonia decomposition activity of Ga-promoted Fe/MgO catalysts
Rein, D. and Friedel Ortega, K. and Weidenthaler, C. and Bill, E. and Behrens, M.
Applied Catalysis A: General 548 (2017)A series of mesoporous MgFe1.75Ga0.25O4 mixed spinel oxides obtained upon calcination of hydrotalcite-like precursors was investigated in the ammonia decomposition reaction at 1 atm after reduction in H2 atmosphere. The corresponding precursors were synthesized from metal salt solutions at five constant pH values in the range between 8.5 and 10.5 by co-precipitation in aqueous media to study the impact of pH variation on the catalyst's structure and activity. N2 physisorption, thermogravimetric analysis, powder X-ray diffraction, Mössbauer spectroscopy, and temperature programmed techniques (H2-TPR and NH3-TPD) were applied to gather information about the textural, (micro-)structural, and adsorption properties of the samples. While phase purity in the precursor and oxide stages is only observed for pH = 10, undesired by-phases (MgFe2O4 and/or Fe3O4) are additionally formed during co-precipitation at the remaining pH values. This is partly related to an incomplete precipitation of Mg2+ cations in less alkaline environments. In situ XRD measurements during reduction revealed that Fe-Ga alloys are formed between 500 and 600 °C. The absence of by-phases avoids the formation of α-Fe, thus improving the structural and compositional homogeneity of the nitridated samples. This beneficial effect is reflected by the low activation energy (70 kJ/mol) and the enhanced low temperature activity (<450 °C) of the phase pure material in the catalytic decomposition of ammonia. © 2017 Elsevier B.V.
view abstract 10.1016/j.apcata.2017.09.004
- 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 abstract 10.1002/anie.201604673
- Complex and liquid hydrides for energy storage
Callini, E. and Atakli, Z.Ö.K. and Hauback, B.C. and Orimo, S.-I. and Jensen, C. and Dornheim, M. and Grant, D. and Cho, Y.W. and Chen, P. and Hjörvarsson, B. and de Jongh, P. and Weidenthaler, C. and Baricco, M. and Paskevicius, M. and Jensen, T.R. and Bowden, M.E. and Autrey, T.S. and Züttel, A.
Applied Physics A: Materials Science and Processing 122 (2016)The research on complex hydrides for hydrogen storage was initiated by the discovery of Ti as a hydrogen sorption catalyst in NaAlH4 by Boris Bogdanovic in 1996. A large number of new complex hydride materials in various forms and combinations have been synthesized and characterized, and the knowledge regarding the properties of complex hydrides and the synthesis methods has grown enormously since then. A significant portion of the research groups active in the field of complex hydrides is collaborators in the International Energy Agreement Task 32. This paper reports about the important issues in the field of complex hydride research, i.e. the synthesis of borohydrides, the thermodynamics of complex hydrides, the effects of size and confinement, the hydrogen sorption mechanism and the complex hydride composites as well as the properties of liquid complex hydrides. This paper is the result of the collaboration of several groups and is an excellent summary of the recent achievements. © 2016, Springer-Verlag Berlin Heidelberg.
view abstract 10.1007/s00339-016-9881-5
- Covalent Attachment of the Water-insoluble Ni(PCy 2NPhe 2)2 Electrocatalyst to Electrodes Showing Reversible Catalysis in Aqueous Solution
Rodríguez-Maciá, P. and Priyadarshani, N. and Dutta, A. and Weidenthaler, C. and Lubitz, W. and Shaw, W.J. and Rüdiger, O.
Electroanalysis 28 (2016)Hydrogenases are a diverse group of metalloenzymes which catalyze the reversible conversion between molecular hydrogen and protons at high rates. The catalytic activity of these enzymes does not require overpotential because their active site has been evolutionarily optimized to operate fast and efficiently. These enzymes have inspired the development of molecular catalysts, which have dramatically improved in efficiency in recent years, to the point that some synthetic catalysts even outperform hydrogenases under certain conditions. In this work, we use a reversible noble-metal-free homogeneous catalyst, the [Ni(PCy 2NPhe 2)2]2+ complex, and we covalently immobilize it on a functionalized highly oriented pyrolytic graphite “edge” (HOPGe) electrode surface. This catalyst is not water soluble, but once it is surface-confined on the electrode, it maintains its catalytic properties in aqueous solutions, showing reversibility for H2 oxidation/reduction. Immobilization of the [Ni(PCy 2NPhe 2)2]2+ complex onto a multi-walled carbon nanotubes coated electrode leads to even higher catalytic current densities and enhanced stability. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/elan.201600306
- 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 abstract 10.1021/jacs.6b04251
- Influence of the degree of infiltration of modified activated carbons with CuO/ZnO on the separation of NO2 at ambient temperatures
Sager, U. and Däuber, E. and Bathen, D. and Asbach, C. and Schmidt, F. and Tseng, J.-C. and Pommerin, A. and Weidenthaler, C. and Schmidt, W.
Adsorption Science and Technology 34 (2016)The reduction of NO2 in air at ambient temperatures with activated carbons can be increased by the infiltration of metal oxide nanoparticles into the sorbents. The NO2 is first adsorbed to the activated carbon and subsequently catalytically reduced to physiologically neutral substances by the metal oxides. The catalytic reduction at ambient temperatures is rather slow. In a former study concerning the application in cabin air filters, it was shown that the modification of activated carbon with 5 wt% CuO/ZnO leads to reduced breakthrough of NO2 and that the adsorbent was able to regenerate between repeated NO2 adsorption cycles. Here we show that the efficiency of the sorbent can be more than doubled by increasing the metal oxide infiltration to 20 wt% whereas a further increase in loading yields no additional improvement, due to a partial transformation of the oxidic compounds. © 2016, © The Author(s) 2016.
view abstract 10.1177/0263617416653120
- 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 abstract 10.1021/acscatal.5b02305
- Molecular structure of diethylaminoalane in the solid state: An X-ray powder diffraction, DFT calculation and Raman spectroscopy study
Bernert, T. and Ley, M.B. and Ruiz-Fuertes, J. and Fischer, M. and Felderhoff, M. and Weidenthaler, C.
Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials 72 (2016)The crystal structure of diethylaminoalane, [H2Al - N(C2H5)2]2, was determined by X-ray powder diffraction in conjunction with DFT calculations. Diethylaminoalane crystallizes in the monoclinic space group P21/c with a = 7.4020 (2), b = 12.9663 (3), c = 7.2878 (2) Å and β = 90.660 (2)° at 293 K. The crystal structure was confirmed by DFT calculations and Raman spectroscopy. The molecular structure of diethylaminoalane consists of dimers of [H2Al - N(CH2CH3)2] in which an Al2N2 four-membered ring is formed by a center of inversion. Such an arrangement of the aminoalane moieties in the crystal structure is well known for this class of compound, as shown by the comparison with ethylmethylaminoalane and diisopropylaminoalane.The crystal structure of diethylaminoalane, [H2Al - N(C2H5)2]2, was determined by X-ray powder diffraction, geometry optimization by density functional theory (DFT) and Raman spectroscopy. The DFT calculations were validated by calculating the ground state structures of two known aminoalanes while the Raman spectrum of diethylaminoalane was measured and compared to the simulated ones. Furthermore, the crystal structure of diethylaminoalane is compared with chemically and structurally similar compounds. © International Union of Crystallography, 2016.
view abstract 10.1107/S2052520616000093
- 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 abstract 10.1002/anie.201511558
- The plastic crystalline A15 phase of dimethylaminoalane, [N(CH3)2-AlH2]3
Ley, M.B. and Bernert, T. and Ruiz-Fuertes, J. and Goddard, R. and Farès, C. and Weidenthaler, C. and Felderhoff, M.
Chemical Communications 52 (2016)A plastic crystalline phase of dimethylaminoalane has been discovered at T > 332 K. The phase transitions solid-plastic phase-liquid are fully reversible. The plastic crystalline phase exhibits a cubic unit cell, space group Pm3n, in which the dimethylaminoalane molecules rotate and adopt a structural arrangement reminiscent of the A15 phase. © 2016 The Royal Society of Chemistry.
view abstract 10.1039/c6cc06166d
- An in situ powder diffraction cell for high-pressure hydrogenation experiments using laboratory X-ray diffractometers
Moury, R. and Hauschild, K. and Kersten, W. and Ternieden, J. and Felderhoff, M. and Weidenthaler, C.
Journal of Applied Crystallography 48 (2015)An in situ diffraction cell is presented which has been designed and constructed for in-house powder diffraction experiments under high gas pressures up to 30MPa. For a proof of principle, the in situ cell has been tested for several hydrogenation experiments under elevated pressures and temperatures. LaNi5 was chosen as an example for hydrogenation, applying simultaneously 5.5MPaH2 pressure at a temperature of 423K. For testing the high-pressure-temperature suitability of the in situ cell, pressure-temperature experiments up to 14MPa at 373K were performed, studying the rehydrogenation of NaH and Al to NaAlH4. The experimental setup enables recording of in situ X-ray diffraction data on laboratory instruments with short data acquisition times at elevated hydrogen pressures and temperatures. © 2015 International Union of Crystallography.
view abstract 10.1107/S1600576714025692
- Controllable Synthesis of Mesoporous Peapod-like Co
3O 4@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 abstract 10.1002/anie.201501475
- Crystal Structure Relation between Tetragonal and Orthorhombic CsAlD4: DFT and Time-of-Flight Neutron Powder Diffraction Studies
Bernert, T. and Krech, D. and Kockelmann, W. and Felderhoff, M. and Frankcombe, T.J. and Weidenthaler, C.
European Journal of Inorganic Chemistry 2015 (2015)The crystal structures of orthorhombic and tetragonal CsAlD4 were refined from time-of-flight neutron powder diffraction data starting from atomic positions predicted from DFT calculations. The earlier proposed crystal structure of orthorhombic CsAlH4 is confirmed. For tetragonal CsAlH4, DFT calculations predicted a crystal structure in I41/amd as potential minimum structure, while from neutron diffraction studies of CsAlD4 best refinement is obtained for a disordered structure in the space group I41/a, with a = 5.67231(9) Å, c = 14.2823(5) Å. While the caesium atoms are located on the Wyckoff position 4b and aluminium at Wyckoff position 4a, there are two distinct deuterium positions at the Wyckoff position 16f with occupancies of 50 % each. From this structure, the previously reported phase transition between the orthorhombic and tetragonal polymorphs could be explained. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/ejic.201500841
- 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 abstract 10.1021/jacs.5b06336
- In Situ X-ray Diffraction Study of Co-Al Nanocomposites as Catalysts for Ammonia Decomposition
Gu, Y.-Q. and Fu, X.-P. and Du, P.-P. and Gu, D. and Jin, Z. and Huang, Y.-Y. and Si, R. and Zheng, L.-Q. and Song, Q.-S. and Jia, C.-J. and Weidenthaler, C.
Journal of Physical Chemistry C 119 (2015)Co-Al nanocomposite materials as active and stable catalysts for ammonia decomposition have been synthesized by a one-pot evaporation-induced self-assembly method. The catalysts were characterized by various techniques including powder X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), N<inf>2</inf> adsorption/desorption, and transmission/scanning electron microscopy (TEM/SEM). Especially, in situ XRD under catalytic reaction conditions was performed, and metallic Co with a cubic structure was identified to be most probably the active crystalline phase for the decomposition of ammonia; also, contribution of CoO to the catalytic activity cannot be excluded. Most importantly, the introduction of alumina can significantly suppress the agglomeration of the active metallic Co phase and thus maintain the high activity of the cobalt catalyst. © 2015 American Chemical Society.
view abstract 10.1021/acs.jpcc.5b02932
- Iron(II) disulfides as precursors of highly selective catalysts for hydrodeoxygenation of dibenzyl ether into toluene
Ji, N. and Wang, X. and Weidenthaler, C. and Spliethoff, B. and Rinaldi, R.
ChemCatChem 7 (2015)In this report, we show that nanocrystalline pyrite and marcasite (FeS2), supported on SBA-15, aerosil SiO2, activated carbon or Al2O3, are precursors of highly active catalysts for the hydrodeoxygenation of dibenzyl ether into toluene. High yields of toluene (up to 100 %) were achieved in experiments performed at 250 C under initial H2 pressure of 100 bar for 2 h. In the recycling experiments, results from XRD and XPS analyses indicate that a fresh surface, formed upon the chemical transformation of FeS2 into Fe(1-x)S, is responsible for the high activity and high selectivity achieved in the conversion of dibenzyl ether into toluene. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/cctc.201500041
- Kinetics enhancement, reaction pathway change, and mechanism clarification in LiBH4 with Ti-catalyzed nanocrystalline MgH2 composite
Shao, H. and Felderhoff, M. and Weidenthaler, C.
Journal of Physical Chemistry C 119 (2015)A composite of 2LiBH4 + nano-MgH2* (Ti-catalyzed) shows significantly enhanced desorption kinetics compared to a conventional mixture of 2LiBH4 + MgH2. The desorption mechanism was studied in the temperature range between 304 and 383 °C and under different pressure conditions. Desorption temperatures are 50-70 °C lower compared to conventional 2LiBH4 + MgH2 mixtures. During the hydrogen release from a mixture of 2LiBH4 + nano-MgH2* at a hydrogen back-pressure of 0.4 MPa, MgB2 is formed and three different plateaus of equilibrium were detected. The reaction pathway is changed at 360 °C for the 2LiBH4 + MgH2 system when the nano-MgH2* is used. © 2015 American Chemical Society.
view abstract 10.1021/jp511479d
- Microstructure analysis of complex CuO/ZnO@carbon adsorbers: What are the limits of powder diffraction methods?
Tseng, J.C. and Schmidt, W. and Sager, U. and Däuber, E. and Pommerin, A. and Weidenthaler, C.
Physical Chemistry Chemical Physics 17 (2015)Activate carbon impregnated with a mixture of copper oxide and zinc oxide performs well as active adsorber for NO<inf>2</inf> removal in automotive cabin air filters. The oxide-loaded activated carbon exhibits superior long-term stability in comparison to pure activated carbon as has been shown in previous studies. The carbon material was loaded only with 2.5 wt% of each metal oxide. Characterization of the oxide nanoparticles within the pores of the activated carbon is difficult because of the rather low concentration of the oxides. Therefore, a systematic study was performed to evaluate the limits of line profile analysis of X-ray powder diffraction patterns. The method allows evaluation of crystalline domain size distributions, crystal defect concentrations and twinning probabilities of nanoscopic materials. Here, the analysis is hampered by the presence of several phases including more or less amorphous carbon. By using physical mixtures of defined copper oxide and zinc oxide particles with activated carbon, potential errors and limits could be identified. The contribution of the activated carbon to the scattering curve was modeled with a convolution of an exponential decay curve, a Chebyshev polynomial, and two Lorentzian peaks. With this approach, domain size distributions can be calculated that are shifted only by about 0.5-1.0 nm for very low loadings (≤4 wt%). Oxide loadings of 4 wt% and 5 wt% allow very reliable analyses from diffraction patterns measured in Bragg-Brentano and Debye-Scherrer geometry, respectively. For the real adsorber material, mean domain sizes have been calculated to be 2.8 nm and 2.4 nm before and after the NO<inf>2</inf> removal tests. © the Owner Societies 2015.
view abstract 10.1039/c5cp01135c
- 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 abstract 10.1002/cctc.201500703
- 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 abstract 10.1002/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 abstract 10.1002/adfm.201302239
- Crystal structure and microstructural changes of molybdenum nitrides traced during catalytic reaction by in situ X-ray diffraction studies
Tagliazucca, V. and Leoni, M. and Weidenthaler, C.
Physical Chemistry Chemical Physics 16 (2014)X-ray diffraction was used to study changes in the crystal structure and microstructure of molybdenum nitrides during ammonia decomposition. In addition, electron microscopy was employed to analyse morphological changes of the nitrides caused by the catalytic reaction. Molybdenum nitride catalysts (Mo xNy) were prepared via high temperature ammonolysis of molybdenum oxide (MoO3) at 650 °C and 800 °C. The materials are nanocrystalline and highly porous, the samples produced at 650 °C still contain the partly reduced precursor (MoO2). In situ X-ray diffraction studies performed on a laboratory instrument equipped with a catalysis reaction chamber reveal significant compositional and structural changes taking place during the reaction. Ball milling, known to enhance the activity of catalysts, has a deleterious effect on the molybdenum nitride specimens: it gives an initial boost due to the reduction of size and increase in dislocation content, but it also favours the formation of the less active hexagonal MoN. This journal is © 2014 the Owner Societies.
view abstract 10.1039/c3cp54578d
- Erratum: Crystal structure and microstructural changes of molybdenum nitrides traced during catalytic reaction by in situ X-ray diffraction studies (Physical Chemistry Chemical Physics (2014) 16 (6182-6188))
Tagliazucca, V. and Leoni, M. and Weidenthaler, C.
Physical Chemistry Chemical Physics 16 (2014)
view abstract 10.1039/c4cp90131b
- Flexibility versus rigidity: What determines the stability of zeolite frameworks? A case study
Verheyen, E. and Joos, L. and Martineau, C. and Dawson, C.J. and Weidenthaler, C. and Schmidt, W. and Yuan, R. and Breynaert, E. and Van Speybroeck, V. and Waroquier, M. and Taulelle, F. and Treacy, M.M.J. and Martens, J.A. and Kirschhock, C.E.A.
Materials Horizons 1 (2014)All silica COK-14/-COK-14 with OKO topology is the first case of a zeolite which reversibly transforms from a systematically interrupted to a fully connected state and back. Analysis of the opening/closing behavior allowed the study of entropy and framework flexibility as determinants for the stability of zeolite topologies, which, until now, has been experimentally inaccessible. Interconversion of the all-silica COK-14 zeolite with fully connected OKO topology and its -COK-14 variant with systematic framework interruption was investigated using high-temperature XRD, thermogravimetric analysis, 29Si MAS NMR, nitrogen adsorption and a range of modelling techniques. Specific framework bonds in the OKO framework can be reversibly hydrolyzed and condensed. Structural silanols of the parent -COK-14, prepared by degermanation of the IM-12 zeolite, were condensed by heating at 923 K, and hydrolyzed again to the initial state by contacting the zeolite with warm water. Molecular modelling revealed an inversion of the relative stabilities for both variants depending on temperature and hydration. Condensation of the structural silanols in -COK-14 to COK-14 is entropy driven, mainly resulting from the release of water molecules. Framework reopening in the presence of water is spontaneous due to the high rigidity of the fully connected OKO framework. Isomorphous substitution was demonstrated as a viable option for stabilization of the fully connected OKO framework as this renders the closed framework flexible. © the Partner Organisations 2014.
view abstract 10.1039/c4mh00127c
- On the preparation and structure of caesium aluminium tetrahydride
Krech, D. and Zibrowius, B. and Weidenthaler, C. and Felderhoff, M.
European Journal of Inorganic Chemistry 2014 (2014)A new tetragonal phase of CsAlH4 was observed after the precipitation of CsAlH4 from a diglyme solution with an inert solvent. This new phase and the previously described orthorhombic phase were characterized by a combination of Xray powder diffraction analysis and 27Al and 133Cs solid-state NMR spectroscopy. The transformation of the tetragonal CsAlH4 phase into the orthorhombic CsAlH4 phase can be induced by thermal treatment, whereas the opposite process can be stimulated by mechanical treatment. The phase transformation processes are almost completely reversible and can be performed several times without any observable decomposition of CsAlH4. The structure of the tetragonal CsAlH4 phase (space group I41/a) was solved from X-ray powder diffraction data, and the lattice parameters were determined to be a = 5.6732(4) and c = 14.2795(11) A. © 2014 Wiley-VCH Verlag GmbH & Co.
view abstract 10.1002/ejic.201402629
- 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 abstract 10.1016/j.apcatb.2014.01.011
- Oxidation of bioethanol using zeolite-encapsulated gold nanoparticles
Mielby, J. and Abildstrøm, J.O. and Wang, F. and Kasama, T. and Weidenthaler, C. and Kegnæs, S.
Angewandte Chemie - International Edition 53 (2014)With the ongoing developments in biomass conversion, the oxidation of bioethanol to acetaldehyde may become a favorable and green alternative to the preparation from ethylene. Here, a simple and effective method to encapsulate gold nanoparticles in zeolite silicalite-1 is reported and their high activity and selectivity for the catalytic gas-phase oxidation of ethanol are demonstrated. The zeolites are modified by a recrystallization process, which creates intraparticle voids and mesopores that facilitate the formation of small and disperse nanoparticles upon simple impregnation. The individual zeolite crystals comprise a broad range of mesopores and contain up to several hundred gold nanoparticles with a diameter of 2-3 nm that are distributed inside the zeolites rather than on the outer surface. The encapsulated nanoparticles have good stability and result in 50%conversion of ethanol with 98% selectivity toward acetaldehyde at 200°C, which (under the given reaction conditions) corresponds to 606 mol acetaldehyde/mol Au hour-1. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA Weinheim.
view abstract 10.1002/anie.201406354
- 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 abstract 10.1038/nmat3872
- 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 abstract 10.1002/anie.201305992
- 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 abstract 10.1021/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 abstract 10.1016/B978-0-08-097774-4.00501-5
- 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 abstract 10.1016/j.jcat.2013.05.011
- 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 abstract 10.1021/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 abstract 10.1002/chem.201103650
- Magnetization enhancement and cation valences in nonstoichiometric (Mn,Fe) 3-δO 4 nanoparticles
Antic, B. and Kremenovic, A. and Jovic, N. and Pavlovic, M.B. and Jovalekic, C. and Nikolic, A.S. and Goya, G.F. and Weidenthaler, C.
Journal of Applied Physics 111 (2012)We present a study of the structural and magnetic properties of (Mn,Fe) 3-δO 4 nanoparticles synthesized by soft mechanochemistry using Mn(OH) 2 × 2 H 2O and Fe(OH) 3 powders as starting compounds. The resulting nanoparticles with a composition of the (Mn,Fe) 3-δO 4 type are found to have a core/shell structure with different Mn/Fe ratios in the core and at the surface. XPS analysis points to valences of 2, 3, and 4 for Mn and 3 for Fe at the particle surface. Combined results of XRPD, Mössbauer spectroscopy, and EDX analysis suggest that there is a deviation from stoichiometry in the nanoparticle core compared to the shell, accompanied by creation of cation polyvalence and vacancies. The value of saturation magnetization, M S, of 73.5 emu/g at room temperature, is among the highest reported so far among nanocrystalline ferrite systems of similar composition. © 2012 American Institute of Physics.
view abstract 10.1063/1.3700228
- 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 abstract 10.1021/jp306166g
- Strontium doping in mullite-type bismuth aluminate: A vacancy investigation using neutrons, photons and electrons
Gesing, T.M. and Schowalter, M. and Weidenthaler, C. and Murshed, M.M. and Nénert, G. and Mendive, C.B. and Curti, M. and Rosenauer, A. and Buhl, J.-C. and Schneider, H. and Fischer, R.X.
Journal of Materials Chemistry 22 (2012)We report on strontium doped dibismuth-nonaoxoaluminate(iii) produced at 1023 K. Partial substitution of bismuth by strontium in the structure yields oxygen vacancies for charge balance. Introducing oxygen vacancies rearranged the associated Al<inf>2</inf>O<inf>7</inf> double-tetrahedra forming "Al <inf>3</inf>O<inf>10</inf>" tri-clusters which were identified by multi-quantum 27Al MAS NMR. Both STEM-EDX and XPS showed homogeneous distribution of strontium in the bulk and on the surface, respectively. Moreover, XPS confirms the valence state of bismuth after doping. The orientations of bismuth 6s2 lone electron pairs were calculated using DFT methods. The amount of strontium in the crystal structure was further confirmed from the decomposition product SrAl<inf>12</inf>O<inf>19</inf> formed during the temperature-dependent X-ray powder diffraction. The structural proof was carried out by refining the structure of (Bi<inf>0.94</inf>Sr <inf>0.06</inf>)<inf>2</inf>Al<inf>4</inf>O<inf>8.94</inf> from powder neutron and X-ray diffraction data. Rietveld refinements clearly showed the under occupation of one oxygen site and the shift of two aluminum atoms from the double-tetrahedra to two tri-cluster sites. © The Royal Society of Chemistry.
view abstract 10.1039/c2jm33208f
- 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 abstract 10.1002/chem.201102718
- 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 abstract 10.1021/ic202492v
- 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 abstract 10.1021/ja2028926
- 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 abstract 10.1002/chem.201001827
- 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 abstract 10.1088/0957-4484/22/23/235401
- Pitfalls in the characterization of nanoporous and nanosized materials
Nanoscale 3 (2011)With the advent of highly sophisticated analytical tools, numerous physical methods are nowadays available for comprehensive characterization of inorganic matter and, as special cases, of porous and nanosized materials. Intelligent experimental setup and correct evaluation of the experimental data can provide helpful insights into the chemical and physical properties of such materials. However, scanning of literature reports shows that in many cases evaluation and interpretation of experimental data are erroneous. As a result, the description of a new material can be useless or even worse, misleading. Wrong evaluation is even more critical if mechanistic theories are based on such data. Characterization of porous and/or nanosized materials is mainly performed by gas adsorption, X-ray powder diffraction, electron microscopy and surface spectroscopy. For correct interpretation of experimental data one should be aware of certain pitfalls. The present paper summarizes prominent faults and may show how they can be avoided. It is supposed to provide some hand-on knowledge on correct analysis of materials. Addressed are primarily non-experts and researchers being new to the field of characterization of inorganic nanosized or nanoporous materials. © 2011 The Royal Society of Chemistry.
view abstract 10.1039/c0nr00561d
- Solid-state hydrogen storage for mobile applications: Quo Vadis?
Weidenthaler, C. and Felderhoff, M.
Energy and Environmental Science 4 (2011)In times of severe shortage of fossil fuels new strategies have to be developed to assure future mobility. Fuel cell driven automotives with hydrogen as an energy carrier is one alternative discussed for the substitution of gasoline in the long term. Both the generation as well as the storage of hydrogen are technical challenges which have to be solved before hydrogen technology can be a real alternative for mobile applications. This perspective paper highlights the state-of-the art in the field of hydrogen storage, especially in solids, including the technical limitations. New potential research fields are discussed which may contribute to future energy supply in niche applications. © 2011 The Royal Society of Chemistry.
view abstract 10.1039/c0ee00771d
- Complex Hydrides
Weidenthaler, C. and Felderhoff, M.
Handbook of Hydrogen Storage: New Materials for Future Energy Storage (2010)
view abstract 10.1002/9783527629800.ch5
- 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 abstract 10.1016/j.scriptamat.2009.12.041
- Facile and reproducible synthesis of ITQ-29 zeolite by using Kryptofix 222 as the structure directing agent
Huang, A. and Weidenthaler, C. and Caro, J.
Microporous and Mesoporous Materials 130 (2010)In pioneering papers Corma et al. reported the synthesis of the Al-free zeolite ITQ-29 with LTA topology by using supramolecular self-assembled molecules as the organic structure directing agent (SDA). However, the SDA used to synthesize ITQ-29 is not commercial and rather difficult to synthesize and purify. Thus the development of a more convenient and more effective method for the synthesis of ITQ-29 is highly desired. Therefore, in this communication we propose a facile and reproducible method to synthesize uniform and well-shaped ITQ-29 crystals by using the crown ether Kryptofix 222 as the SDA. © 2009 Elsevier Inc. All rights reserved.
view abstract 10.1016/j.micromeso.2009.10.021
- 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 abstract 10.1016/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 abstract 10.1021/jp106436h
- 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 abstract 10.1021/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 abstract 10.1016/j.apcata.2010.07.036
- 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 abstract 10.1021/ja105308e
- 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 abstract 10.1021/cm100277k