Remarkable spreading behavior of molybdena on silica catalysts: an in situ EXAFS-Raman study

M. Boer, de, A.J. Dillen, van, D.C. Koningsberger, J.W. Geus, M.A. Vuurman, I.E. Wachs

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In contrast to the frequently reported lack of interaction between hexavalent Mo and SiO2 and the tendency of SiO2 supported MoO3 to coalescence, it has been found that on dehydration small Mo oxide clusters spread over a SiO2 support. A combined Raman spectroscopy-x-ray absorption study shows a significantly altered structure of the Mo oxide phase after dehydration. In EXAFS the total Mo-Mo coordination no. drops from 3.27 to 0.20 after an in situ thermal treatment at 673 K. The increase of the peak in the XANES region (1s -> 4d) indicates that the coordination sphere of the Mo atoms strongly alters after dehydration. The Raman spectra reflect the change of the structure through a shift of the position of the terminal Mo:O bond from 944 986 cm-1 and the disappearance of the bridged Mo-O-Mo vibration at 880 cm-1. Dehydration produces almost isolated Mo sites in this highly dispersed sample. Water ligands stabilize the oligomeric clusters under ambient conditions; the removal of water causes spreding of these clusters. [on SciFinder (R)]
Original languageEnglish
Pages (from-to)227-239
JournalCatalysis Letters
Issue number2
Publication statusPublished - 1991


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