Surface heterogeneity of zirconia-supported V{sub 2}O{sub 5} catalysts. The link between structure and catalytic properties in oxidative dehydrogenation of propane
Undoped and alkali-doped zirconia-supported vanadia catalysts for the oxidative dehydrogenation of propane were prepared by impregnation and characterized by various techniques. The chemical state of surface and bulk vanadium was investigated as a function of the calcination temperature, V{sub 2}O{sub 5} loading, and the nature and content of alkali-metal additives. It is found that on the surface vanadium is present in the form of isolated vanadyl species or oligomeric vanadates, or as nanocrystalline V{sub 2}O{sub 5} and that V{sup 5+} and V{sup 4+} ions coexist in octahedral and tetrahedral coordination, while within the bulk of zirconia matrix, V{sup 4+} ions are stabilized in a V{sub x}Zr{sub 1{minus}x}O{sub 2} solid solution. Presence of the alkali-metal additives and water changes the dispersion of surface vanadium species favoring, in both cases, formation of mononuclear vanadyl surface complexes. Surface heterogeneity plays a vital role for the catalytic performance of V{sub 2}O{sub 5}/ZrO{sub 2} catalysts in oxidative dehydrogenation of propane. Catalytic properties are related to the nature of VO{sub x} surface species and correlates well with their reducibility. The maximum of catalytic activity was observed for catalysts with vanadia content between 3 and 5 mol %, for which octahedral polyvanadate surface species are dominant. It is proposed that the catalytic activity is affected by the nucleophilicity of bridging oxygen in V-O-V entities, modified by the adjacent alkali cations.
- Research Organization:
- Jagiellonia Univ., Cracow (PL)
- OSTI ID:
- 20000515
- Report Number(s):
- CONF-9808111-; LANGD5
- Journal Information:
- Langmuir, Vol. 15, Issue 18; Conference: Third international symposium on effects of surface heterogeneity in adsorption and catalysis on solids, Torun (PL), 08/09/1998--08/16/1998; Other Information: PBD: 31 Aug 1999; ISSN 0743-7463
- Country of Publication:
- United States
- Language:
- English
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