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Fundamental Studies of Butane Oxidation over Model-Supported Vanadium Oxide Catalysts: Molecular Structure-Reactivity Relationships

By I.E. Wachs, J.M. Jehng, G. Deo, B.M. Weckhuysen, V.V. Guliants, J.B. Benziger and S. Sundaresan


The oxidation of n-butane to maleic anhydride was investigated over a series of model-supported vanadia catalysts where the vanadia phase was present as a two-dimensional metal oxide overlayer on the different oxide supports (TiO2, ZrO2, CeO2, Nb2O5, Al2O3, and SiO2). No correlation was found between the properties of the\ud terminal V==O bond and the butane oxidation turnover frequency (TOF) during in situ Raman spectroscopy study. Furthermore, neither the n-butane oxidation TOF nor maleic anhydride selectivity was related to the extent of reduction of the surface vanadia species. The n-butane oxidation TOF was essentially independent of the surface vanadia coverage, suggesting that the n-butane activation requires only one surface vanadia site. The maleic anhydride TOF,\ud however, increased by a factor of 2–3 as the surface vanadia coverage was increased to monolayer coverage. The higher maleic anhydride TOF at near monolayer coverages suggests that a pair of adjacent vanadia sites may efficiently oxidize n-butane to maleic anhydride, but other factors may also play a contributing role (increase in surface Brønsted acidity and decrease in the number of exposed support cation sites). Varying the specific oxide support changed\ud the n-butane oxidation TOF by ca. 50 (Ti>Ce>Zr~Nb>Al>Si)as well as the maleic anhydride selectivity. The maleic anhydride\ud selectivity closely followed the Lewis acid strength of the oxide support cations, Al> Nb> Ti> Si> Zr> Ce. The addition of\ud acidic surface metal oxides (W, Nb, and P) to the surface vanadia layer was found to have a beneficial effect on the n-butane\ud oxidation TOF and the maleic anhydride selectivity. The creation of bridging V–O–P bonds had an especially positive effect on the maleic anhydride selectivity

Topics: Scheikunde
Year: 1997
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