On the Mechanism of n-Butane Oxidation to Maleic Anhydride on VPO Catalysts. II. Study of the Evolution of the VPO Catalysts under n-Butane, Butadiene, and Furan Oxidation Conditions

Article abstract of DOI:10.1006/jcat.1994.1034

The evolution of the VOPO4 phases and of (VO)2P2O7 and the activated VPO catalyst has been studied by XRD, 31P MAS-NMR, laser Raman spectroscopy, and electron spin resonance after the oxidation of butane, butadiene, and furan.With the exception of δ VOPO4, which partly changes to α_II VOPO4, almost no evolution of the bulk structure has been observed.It is concluded that the mechanism of butane oxidation on the VPO catalyst implies principally the participation of a limited number of superficial layers of the structure.Catalytic properties depend on the redox properties of a limited number of V⁵⁺ ensembles on the (VO)2P2O7 matrix.A proposal for the mechanism of n-butane oxidation which implies an alkoxide route is presented.