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  Structural Analysis of Silica-Supported Molybdena Based on X-ray Spectroscopy: Quantum Theory and Experiment

Guo, C., Hermann, K., Hävecker, M., Thielemann, J. P., Kube, P., Gregoriades, L. J., et al. (2011). Structural Analysis of Silica-Supported Molybdena Based on X-ray Spectroscopy: Quantum Theory and Experiment. The Journal of Physical Chemistry C, 115, 15449-15458. doi:10.1021/jp2034642.

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 Creators:
Guo, Chunsheng1, Author           
Hermann, Klaus1, Author           
Hävecker, Michael2, Author           
Thielemann, Joerg Philipp2, Author           
Kube, Pierre2, Author           
Gregoriades, Laurence J.3, Author
Trunschke, Annette2, Author           
Sauer, Joachim3, Author
Schlögl, Robert2, Author           
Affiliations:
1Theory, Fritz Haber Institute, Max Planck Society, ou_634547              
2Inorganic Chemistry, Fritz Haber Institute, Max Planck Society, ou_24023              
3Humboldt University, Unter den Linden 6, 10099 Berlin, Germany, ou_persistent22              

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 Abstract: Oxygen core excitations in different molecular molybdena silica models are evaluated using density-functional theory (DFT). These results can be compared with in situ X-ray absorption fine structure (NEXAFS) measurements near the O K-edge of molybdena model catalysts supported on SBA-15 silica, used for exploratory catalytic activity studies. The comparison allows an analysis of structural details of the molybdena species. The silica support is found to contribute to the NEXAFS spectrum in an energy range well above that of the molybdena units, allowing a clear separation between the corresponding contributions. Different types of oxygen species, O(1) in terminal MdO bonds, O(2) in interphase Mo—O—Si bridges and in Mo—O—Mo linkages, as well as O(2) in terminal Mo—O—H groups can be distinguished in the theoretical spectra of the molybdena species with molybdenum in tetrahedral (dioxo species), pentahedral (monooxo species), and octahedral coordination. The experimental NEXAFS spectra exhibit a pronounced double-peak structure in the O 1s to Mo 4dO 2p excitation range of 529 536 eV. Comparison with the present theoretical data gives clear indications that dioxo molybdena species with tetrahedral MoO4 units can explain the experimental spectrum. This does not fully exclude species with other Mo coordination, like pentahedral. However, the latter are believed to exist in the present samples in much smaller amounts. The experimental NEXAFS spectrum for the supported molybdena species differs substantially from that for MoO3 bulk material with octahedral MoO6 units where the observed asymmetric peak structure is also reproduced by the calculations.

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Language(s): eng - English
 Dates: 2011-04-132011-07-052011
 Publication Status: Published in print
 Pages: 10
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1021/jp2034642
 Degree: -

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Title: The Journal of Physical Chemistry C
  Other : J. Phys. Chem. C
Source Genre: Journal
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Publ. Info: Washington DC : American Chemical Society
Pages: - Volume / Issue: 115 Sequence Number: - Start / End Page: 15449 - 15458 Identifier: ISSN: 1932-7447
CoNE: https://pure.mpg.de/cone/journals/resource/954926947766