title: Atomic-Scale Determination of Active Facets on the MoVTeNb Oxide M1 Phase and Their Intrinsic Catalytic Activity for Ethane Oxidative Dehydrogenation.
abstract: Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) has been used to image the basal {001} plane of the catalytically relevant M1 phase in MoVTeNb complex oxides. Facets {010}, {120}, and {210} are identified as the most frequent lateral termination planes of the crystals. Combination of STEM with He ion microscopy (HIM) images, Rietveld analysis, and kinetic tests reveals that the activation of ethane is correlated to the availability of facets {001}, {120}, and {210} at the surface of M1 crystals. The lateral facets {120} and {210} expose crystalline positions related to the typical active centers described for propane oxidation. Conversely, the low activity of the facet {010} is attributed to its configuration, consisting of only stable M6 O21 units connected by a single octahedron. Thus, we quantitatively demonstrated that differences in catalytic activity among M1 samples of equal chemical composition depend primarily on the morphology of the particles, which determines the predominant terminating facets.
authors.affiliation: Department of Chemistry and Catalysis Research Center, Technische Universität München, Lichtenbergstraße 4, 85748, Garching, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Melzer
authors.affiliation: Department of Chemical Engineering and Materials Science, University of California, Davis, One Shields Avenue, Davis, CA, 95616, USA.
authors.forename: Pinghong
authors.initials: P
authors.lastname: Xu
authors.affiliation: Department of Chemistry and Catalysis Research Center, Technische Universität München, Lichtenbergstraße 4, 85748, Garching, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Hartmann
authors.affiliation: Fundamental and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Fundamental and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA, 99352, USA. nigel.browning@pnnl.gov.
authors.forename: Nigel D
authors.initials: ND
authors.lastname: Browning
authors.affiliation: Department of Chemistry and Catalysis Research Center, Technische Universität München, Lichtenbergstraße 4, 85748, Garching, Germany. m.sanchez@tum.de.
authors.forename: Maricruz
authors.initials: M
authors.lastname: Sanchez-Sanchez
authors.affiliation: Department of Chemistry and Catalysis Research Center, Technische Universität München, Lichtenbergstraße 4, 85748, Garching, Germany. johannes.lercher@ch.tum.de.
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Lercher
mesh_terms: D002384:Catalysis; D006865:Hydrogenation; D017348:Microscopy, Electron, Scanning Transmission; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D010087:Oxides; D028561:Transition Elements
keywords: heterogeneous catalysis; oxidative dehydrogenation; scanning probe microscopy; surface chemistry; surface structures