Structure and properties of vanadium oxide-zirconia catalysts for propane oxidative dehydrogenation
- Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.
The structure of vanadia species supported on zirconia depends on VO{sub x} surface density and on the temperature of catalyst oxidation pretreatments. X-ray diffraction and Raman and UV-visible spectroscopies show that supported VO{sub x} species form polyvanadate domains of increasing size and ultimately monolayers and clusters as vanadium surface density increases. Initial propene selectivities in oxidative dehydrogenation of propane at 606 K increase with increasing VO{sub x} surface density and reach constant values of 80% at surface densities of about 2--3 VO{sub x}/nm{sup 2}. High selectivities to CO{sub x} products at low surface densities and on bulk ZrV{sub 2}O{sub 7} appear to be associated with exposed unselective V-O-Zr and Zr-O-Zr sites. Propane oxidative dehydrogenation rates increase initially as the size of polyvanadate domains increases with increasing VO{sub x} surface density. Oxidative dehydrogenation rates decreases eventually as the formation of V{sub 2}O{sub 5} clusters at high surface densities leads to a decrease in the fraction of VO{sub x} exposed at cluster surfaces. The ratio of rate constants for propane oxidative dehydrogenation and propene combustion to CO{sub x} remains constant throughout the entire range of VO{sub x} surface density (0.4--100 VO{sub x}/nm{sup 2}), suggesting that primary oxidative dehydrogenation steps and secondary oxidation reactions of desired propene products require identical polyvanadate structures.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 653324
- Journal Information:
- Journal of Catalysis, Vol. 177, Issue 2; Other Information: PBD: 25 Jul 1998
- Country of Publication:
- United States
- Language:
- English
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