First crystal structure studies of CaAlH5

A new member of the aluminum hydride family, CaAlH5, is formed during the decomposition of Ca(AlH4)2. The crystal structure of this new compound was calculated by density functional theory band-structure calculations and confirmed by X-ray powder diffraction analysis. The structure crystallizes in space group P21/n (No. 14), with a = 8.3797(9) Å, b = 6.9293(8) Å, c = 9.8138(11) Å, β = 93.78(1)°, and Z = 8

One Pot Cooperation of Single Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization - Hydrosilylation Process

[EN] 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 Ru-1/CeO2 and Rh-1/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 alpha-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.X-ray absorption experiments were performed at the ALBA Synchrotron Light Source (Spain), experiments 2018082961 and 2019023278. L. Simonelli and C. Marini (CLAESSALBA beamline) are thanked for beamline setup. E. Andres, M. E. Martinez, M. Garcia, and I. Lopez (ITQ), are acknowledged for their assistance with XAS experiments. J. Buscher, J. Ternedien, B. Spliethoff, and C. Wirtz (MPI-KOFO) are acknowledged for the performance of XPS, XRD, BF-TEM and 2H NMR experiments, respectively. I. C. de Freitas (MPIKOFO) is thanked for assistance with Raman spectroscopy. J. M. Salas (ITQ) is gratefully acknowledged for his contribution to CO-FTIR experiments. J. J. Barnes and Shell (Amsterdam) are acknowledged for kindly providing an industrial olefin mixture as feed. Authors are thankful to F. Schuth for the provision of lab space and continued support. Part of the HRSTEM and EDX-STEM studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Spain. R.A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016-79776-P (AEI/FEDER, UE) and from the European Union H2020 programs "ESTEEM3" (823717). The authors acknowledge support by the state of Baden-Wurttemberg through bwHPC (bwUnicluster and JUSTUS, RV bw17D01), by the GRK 2450 and by the Helmholtz Association. This research received funding from the Max Planck Society, and the Fonds der Chemische Industrie of Germany. Funding from the Spanish Ministry of Science, Innovation and Universities (Severo Ochoa program SEV-2016-0683 and grant RTI2018096399-A-I00) is also acknowledged. B.B.S. acknowledges the Alexander von Humboldt Foundation for a postdoctoral scholarship. Open Access funding is provided by the Max Planck Society.Sarma, BB.; Kim, J.; Amsler, J.; Agostini, G.; Weidenthaler, C.; Pfaender, N.; Arenal, R.... (2020). One Pot Cooperation of Single Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization - Hydrosilylation Process. Angewandte Chemie International Edition. 59(14):5806-5815. https://doi.org/10.1002/anie.201915255S580658155914Liang, S., Hao, C., & Shi, Y. (2015). The Power of Single-Atom Catalysis. ChemCatChem, 7(17), 2559-2567. doi:10.1002/cctc.201500363Liu, J. (2016). Catalysis by Supported Single Metal Atoms. 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Strontium doping in mullite-type bismuth aluminate: A vacancy investigation using neutrons, photons and electrons

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 Al2O7 double-tetrahedra forming “Al3O10” 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 SrAl12O19 formed during the temperature-dependent X-ray powder diffraction. The structural proof was carried out by refining the structure of (Bi0.94Sr0.06)2Al4O8.94 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

Synthetic ferripyrophyllite: preparation, characterization and catalytic application

[EN] 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 authors gratefully acknowledge the following people for support with analytical measurements and data analysis: Hans-Josef Bongard (SEM-EDX), Silvia Palm (EDX bulk), Adrian Schluter (TEM), Norbert Pfander (STEM), Jan Ternieden and Jan Nicolas Buscher (XRD and XPS), Prof. Dr Osamu Terasaki and Dr Yanghang Ma (3D electron diffraction tomography: failed due to the poor crystallinity and stability under strong beam irradiation), Dr Nicolas Duyckaerts (NH3-TPD measurements), Kai Jeske (GC gas analysis), Dr Yuxiao Ding (ATR-IR) and Dr Zhengwen Cao (titration). The authors also would like to thank Prof. Dr Robert Schlogl, Dr Thomas Lunkenbein, Fabian Pienkoss and Dr Gaetano Calvaruso for helpful and enthusiastic discussions, as well as Niklas Fuhrmann and Lars Winkel for technical support. The studies were carried out as part of our activities in the Cluster of Excellence "Tailor-Made Fuels from Biomass" (EXC 236) and "The Fuel Science Center" funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy -Exzellenzcluster 2186 "The Fuel Science Center" ID: 390919832. Open Access funding provided by the Max Planck Society.Qiao, Y.; Theyssen, N.; Spliethoff, B.; Folke, J.; Weidenthaler, C.; Schmidt, W.; Prieto González, G.... (2021). Synthetic ferripyrophyllite: preparation, characterization and catalytic application. Dalton Transactions. 50(3):850-857. https://doi.org/10.1039/d0dt03125aS85085750

The Impact of Antimony on the Performance of Antimony Doped Tin Oxide Supported Platinum for the Oxygen Reduction Reaction

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

Hydrogen storage in liquid hydrogen carriers: recent activities and new trends

Efficient storage of hydrogen is one of the biggest challenges towards a potential hydrogen economy. Hydrogen storage in liquid carriers is an attractive alternative to compression or liquefaction at low temperatures. Liquid carriers can be stored cost-effectively and transportation and distribution can be integrated into existing infrastructures. The development of efficient liquid carriers is part of the work of the International Energy Agency Task 40: Hydrogen-Based Energy Storage. Here, we report the state-of-the-art for ammonia and closed CO2-cycle methanol-based storage options as well for liquid organic hydrogen carriers

Materials for hydrogen-based energy storage - past, recent progress and future outlook

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

Systematic in situ Investigation of the Formation of NH3_3 Cracking Catalysts from Precursor Perovskites ABO3_3 (A=La,Ca,Sr and B=Fe,Co,Ni) and their Catalytic Performance

This work addresses the formation of ammonia (NH$_3$) decomposition catalysts derived from perovskites ABO$_3$ (A=La, Ca, Sr, and B=Fe, Co, Ni) precursors via operando synchrotron X-ray diffraction experiments. During the reaction in NH$_3$, the perovskite precursors are decomposed and the transition metals are reduced. Depending on their reduction properties, active metallic catalysts are formed in situ on La$_2$O$_3$ as support. The reduction behavior of the perovskites, formation of intermediate phases during activation, and catalytic performance was studied in detail. In addition, microstructure properties such as crystallite sizes and particle morphology were analyzed. Co-/Ni-based perovskites decomposed completely during activation to Co$_0$/Ni$_0$ supported on La$_2$O$_3$ while Fe-based perovskites were fully stable but inactive in catalysis. This difference is due to varying electronic properties of the transition metals, e. g., decreasing electronegativity from Ni to Fe. With decreasing reducibility, the intermediate phases during activation formed more distinct. La$^{3+}$ was partially substituted by Ca$^{2+}$/Sr$^{2+}$ in LaCoO$_3$ to test for advantageous effects in NH$_3$ decomposition. The best performance was observed using the precatalyst La$_{0.8}$Sr$_{0.2}$CoO$_3$ with a conversion of 86 % (100 % NH$_3$, 15000 mL g$^{−1}$ h$^{−1}$) at 550 °C