Surface structures of supported molybdenum oxide catalysts. Characterization by Raman and Mo L{sub 3}-edge XANES
- Lehigh Univ., Bethlehem, PA (United States)
- Dow Chemical Co., Midland, MI (United States)
Supported molybdenum oxide catalysts on TiO{sub 2}, Al{sub 2}O{sub 3}, ZrO{sub 2}, SiO{sub 2}, and Nb{sub 2}0s were prepared by the incipient-wetness impregnation method employing aqueous solutions of ammonium heptamolybdate ((NH{sub 4}){sub 6}Mo{sub 7}O{sub 24}{center_dot}H{sub 2}O). The molecular structures of the surface molybdenum oxide species were investigated. Under ambient conditions, the structures of the hydrated surface molybdenum oxide species are controlled by the net surface pH at the point of zero charge (PZC) and are the same as observed in aqueous solutions: MoO{sub 4}{sup 2-}, Mo{sub 7}O{sub 24}{sup 6-}, and Mo{sub 8}O{sub 26}{sup 4-}. Under dehydrated conditions, the structures of the surface molybdenum oxide species depend on both the specific oxide support and surface coverage. At low surface coverages of MoO{sub 3} on Al{sub 2}O{sub 3} and TiO{sub 2} the primary species is isolated and tetrahedral coordinated. At high surface coverages of MoO{sub 3}, for TiO{sub 2} the primary species is polymerized and octahedral coordinated, but for Al{sub 2}O{sub 3} there is a mixture of tetrahedral and octahedral coordinated species. The surface molybdenum oxide species on SiO{sub 2} is isolated and appears to possess a coordination that is in between tetrahedral and octahedral. Monolayer coverage was achieved at the same surface density of molybdenum oxide on the different oxide supports with the exception of SiO{sub 2}. 90 refs., 18 figs., 5 tabs.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 81326
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 27 Vol. 99; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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