Dynamics of CrO3–Fe2O3 catalysts during the high-temperature water-gas shift reaction: molecular structures and reactivity

A series of supported CrO3/Fe2O3 catalysts were investigated for the high-temperature water-gas shift (WGS) and reverse-WGS reactions and extensively characterized using in situ and operando IR, Raman, and XAS spectroscopy during the high-temperature WGS/RWGS reactions. The in situ spectroscopy examinations reveal that the initial oxidized catalysts contain surface dioxo (O═)2Cr6+O2 species and a bulk Fe2O3 phase containing some Cr3+ substituted into the iron oxide bulk lattice. Operando spectroscopy studies during the high-temperature WGS/RWGS reactions show that the catalyst transforms during the reaction. The crystalline Fe2O3 bulk phase becomes Fe3O4 ,and surface dioxo (O═)2Cr6+O2 species are reduced and mostly dissolve into the iron oxide bulk lattice. Consequently, the chromium–iron oxide catalyst surface is dominated by FeOx sites, but some minor reduced surface chromia sites are also retained. The Fe3–-xCrxO4 solid solution stabilizes the iron oxide phase from reducing to metallic Fe0 and imparts an enhanced surface area to the catalyst. Isotopic exchange studies with C16O2/H2 → C18O2/H2 isotopic switch directly show that the RWGS reaction proceeds via the redox mechanism and only O* sites from the surface region of the chromium–iron oxide catalysts are involved in the RWGS reaction. The number of redox O* sites was quantitatively determined with the isotope exchange measurements under appropriate WGS conditions and demonstrated that previous methods have undercounted the number of sites by nearly 1 order of magnitude. The TOF values suggest that only the redox O* sites affiliated with iron oxide are catalytic active sites for WGS/RWGS, though a carbonate oxygen exchange mechanism was demonstrated to exist, and that chromia is only a textural promoter that increases the number of catalytic active sites without any chemical promotion effect

TISSUE DECELLULARIZATION METHODS

Provided herein are methods of producing an acellular tissue product wherein the method can include the step of inducing apoptosis and washing the tissue after induction of apoptosis with a tonic solution. Also provided herein are acellular tissue products produced by the methods provided herein and methods of administering the acellular tissue products to a subject in need thereof

Looking back to see the future: building nuclear power plants in Europe

The so-called ‘nuclear renaissance’ in Europe is promulgated by the execution of two large engineering projects involving the construction of two European Pressurized Reactors (EPRs) in Flamanville, France and Olkiluoto in Finland. As both projects have faced budget overruns and delays, this paper analyses their governance and history to derive lessons useful for the construction of future projects. Analysis indicates that the reasons for these poor outcomes are: overoptimistic estimations, first-of-a-kind (FOAK) issues and undervaluation of regulation requirements. These pitfalls have the potential to impact on many other engineering construction projects and highlight fruitful areas of further research into project performance

Five-Torsion in the Homology of the Matching Complex on 14 Vertices

J. L. Andersen proved that there is 5-torsion in the bottom nonvanishing homology group of the simplicial complex of graphs of degree at most two on seven vertices. We use this result to demonstrate that there is 5-torsion also in the bottom nonvanishing homology group of the matching complex $M_{14}$ on 14 vertices. Combining our observation with results due to Bouc and to Shareshian and Wachs, we conclude that the case $n=14$ is exceptional; for all other $n$, the torsion subgroup of the bottom nonvanishing homology group has exponent three or is zero. The possibility remains that there is other torsion than 3-torsion in higher-degree homology groups of $M_n$ when $n \ge 13$ and $n \neq 14$.Comment: 11 page

Anomalous reactivity of supported V2O5 nanoparticles for propane oxidative dehydrogenation: influence of the vanadium oxide precursor

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The oxidative dehydrogenation (ODH) of propane to propylene by supported vanadia catalysts has received much attention in recent years, but different reactivity trends have been reported for this catalytic reaction system. In the present investigation, the origin of these differing trends are investigated with synthesis of supported V/SiO2, V/TiO2, and V/Al2O3 catalysts prepared with three different vanadium oxide precursors (2-propanol/vanadyl triisopropoxide [VO(O-Pri)3] (VTI), oxalic acid/ammonium metavanadate [NH4VO3] (AMV), and toluene/vanadyl acetylacetonate [VO(C5H7O2)2] (VAA)) in order to elucidate the influence of the precursor on supported vanadia phase and propane ODH activity. In situ Raman spectroscopy revealed that the choice of vanadium precursor does not affect the dispersion of the supported vanadium oxide phase below 4 V nm−2 (0.5 monolayer coverage), where only isolated and oligomeric surface VO4 species are present, and only the AMV precursor favors crystalline V2O5 nanoparticle (NP) formation below monolayer coverage (8 V nm−2). The propane ODH specific reactivity trend demonstrated that there is no significant difference in TOF for the isolated and oligomeric surface VO4 sites. Surprisingly, V2O5 NPs in the ∼1–2 nm range exhibit anomalously high propane ODH TOF values for the supported vanadia catalysts. This was found for all supported vanadium oxide catalysts examined. This comparative study with different V-precursors and synthesis methods and oxide supports finally resolves the debate in the catalysis literature about the dependence of TOF on the surface vanadium density that is related to the unusually high reactivity of small V2O5 NPs.DFG, SFB 546, Struktur, Dynamik und Reaktivität von Übergangsmetalloxid-Aggregate

Nature of catalytically active sites in the supported WO3/ZrO2 solid acid system: a current perspective

Tungstated zirconia (WO3/ZrO2) is one of the most well-studied solid acid catalyst systems and continues to attract the attention of both academia and industry. Understanding and controlling the properties of WO3/ZrO2 catalysts has been a topic of considerable interest over almost the past three decades, with a particular focus on discovering the relationship between catalytic activity and the molecular structure of the surface acid site. Amorphous tungsten oxide (WOx) species on ZrO2 surfaces were previously proposed to be very active for different acidic reactions such as alcohol dehydration and alkane isomerization. Recent developments in electron optical characterization and in situ spectroscopy techniques have allowed researchers to isolate the size, structure, and composition of the most active catalytic species, which are shown to be three-dimensional distorted Zr-WOx clusters (0.8–1.0 nm). Complementary theoretical calculations of the Brønsted acidity of these Zr-WOx clusters have confirmed that they possess the lowest deprotonation energy values. This new insight provides a foundation for the future characterization and theory of acidic supported metal oxide catalytic materials that will, hopefully, lead to the design of more active and selective catalysts. This perspective presents an up-to-date, comprehensive summary of the leading models of WO3/ZrO2 solid acid catalysts

Anomalous Surface Compositions of Stoichiometric Mixed Oxide Compounds

The surface compositions of bulk mixed metal oxides stoichiometric vanadate and molybdate compounds have been systematically examined, for the first time, by combined synchroton-based depth-resolved XPS profile analysis, conventional XPS and LEIS spectroscopy. The outer surfaces of many, but not all, of the bulk mixed vanadates and molybdates tend to be enriched with surface VOx and MoOx species approaching monolayer coverage. Furthermore, this surface enrichment phenomenon can be dramatically enhanced in the presence of minor amount of alkali impurities. These new findings have significant implications for the fundamental understanding of how bulk mixed oxide materials function in numerous technical applications.Fil: Merzlikin, Sergiy V. . Ruhr-Universitt Bochum, Lehrstuhl fr Technische Chemie; AlemaniaFil: Tolkachev, Nikolay N. . Russian Academy of Sciences, N. D. Zelinsky Institute of Organic Chemistry; RusiaFil: Briand, Laura Estefania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Strunskus,Thomas . Ruhr-Universitt Bochum, Lehrstuhl Physikalische Chemie; AlemaniaFil: Wöll, Christof. Ruhr-Universitt Bochum, Lehrstuhl Physikalische Chemie; AlemaniaFil: Wachs, Israel E.. Lehigh University Bethlehem, Department of Chemical Engineering, Operando Molecular Spectroscopy and Catalysis Laboratory; Estados UnidosFil: Grüenert, Wolfgang . Ruhr-Universitt Bochum, Lehrstuhl fr Technische Chemie; Alemani

Anomalous Surface Compositions of Stoichiometric Mixed Oxide Compounds

The surface compositions of bulk mixed metal oxides stoichiometric vanadate and molybdate compounds have been systematically examined, for the first time, by combined synchroton-based depth-resolved XPS profile analysis, conventional XPS and LEIS spectroscopy. The outer surfaces of many, but not all, of the bulk mixed vanadates and molybdates tend to be enriched with surface VOx and MoOx species approaching monolayer coverage. Furthermore, this surface enrichment phenomenon can be dramatically enhanced in the presence of minor amount of alkali impurities. These new findings have significant implications for the fundamental understanding of how bulk mixed oxide materials function in numerous technical applications.Fil: Merzlikin, Sergiy V. . Ruhr-Universitt Bochum, Lehrstuhl fr Technische Chemie; AlemaniaFil: Tolkachev, Nikolay N. . Russian Academy of Sciences, N. D. Zelinsky Institute of Organic Chemistry; RusiaFil: Briand, Laura Estefania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Strunskus,Thomas . Ruhr-Universitt Bochum, Lehrstuhl Physikalische Chemie; AlemaniaFil: Wöll, Christof. Ruhr-Universitt Bochum, Lehrstuhl Physikalische Chemie; AlemaniaFil: Wachs, Israel E.. Lehigh University Bethlehem, Department of Chemical Engineering, Operando Molecular Spectroscopy and Catalysis Laboratory; Estados UnidosFil: Grüenert, Wolfgang . Ruhr-Universitt Bochum, Lehrstuhl fr Technische Chemie; Alemani