Surface aspects of bismuth-metal oxide catalysts
- Lehigh Univ., Bethlehem, PA (United States); and others
A series of conventional and model bismuth-metal oxide catalysts (vanadates, molybdates, tungstates, and niobates) were physically and chemically characterzied (Raman spectroscopy, BET, XPS, and methanol oxidation) to obtain additional insights into the structure-reactivity relationships of such catalytic materials. The reactivity for methanol oxidation over the conventional bismuth-metal oxide catalysts was found to be primarily related to the surface area of the oxide catalysts and was essentially independent of the near surface composition and the bulk structure. The selectivity for methanol oxidation over the conventional bismuth-metal oxide catalysts was essentially found not to be a function of the surface area, the near surface composition, and the bulk structure. A series of model bismuth-metal oxide catalysts was synthesized by depositing metal oxides on the surface of a bismuth oxide support. The model studies demonstrated that two-dimensional metal oxide overlayers are not stable on the bismuth oxide support and readily react to form bulk bismuth-metal oxide compounds upon heating. Furthermore, the model studies revealed that these bulk bismuth-metal oxide compounds are related to the active sites for the partial oxidation reaction. In situ Raman spectroscopy in methanol/oxygen, methanol, and oxygen reaction environments with helium as the diluent revealed no additional information regarding the nature of the active site. It was found that only highly crystalline bismuth-metal oxide phases are selective for the partial oxidation of methanol to formaldehyde. Thus, selective bismuth-metal oxide catalysts will always possess highly crystalline metal oxide phases containing extremely low surface areas which make it difficult to obtain fundamental surface information about the outermost layers. 48 refs., 11 figs., 9 tabs.
- OSTI ID:
- 264065
- Journal Information:
- Journal of Catalysis, Vol. 159, Issue 1; Other Information: PBD: Mar 1996
- Country of Publication:
- United States
- Language:
- English
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