Ethane and n-butane oxidation over supported vanadium oxide catalysts: An in situ UV-visible diffuse reflectance spectroscopic investigation

The coordination/oxidation states of surface vanadium oxide species on seve ral oxide supports (Al2O3, ZrO2, SiO2) during ethane and n-butane oxidation were examined by in situ UV-vis diffuse reflectance spectroscopy (DRS). On ly a small amount of the surface V(V) cations are reduced to V(IV)/V(III) c ations under present steady-state reaction conditions. The extents of reduc tion of the surface V(V) species are a strong function of the specific oxid e support, V2O5/ZrO2 > V2O5/Al2O3 > V2O5/SiO2, and also correlate with thei r reactivities (turnover frequencies) for ethane and n-butane oxidation rea ctions. For ZrO2-supported samples, the polymerized surface vanadia species were found to be more easily reduced than the isolated surface vanadia spe cies in reducing environments (i.e., ethane or n-butane in He), but no sign ificant differences in the extents of reduction were observed under present steady-state reaction conditions (i.e., ethane/O-2/He or n-butane/O-2/He). This observation is also consistent with the ethane oxidation catalytic st udy, which revealed that the polymerization degree, the domain size, of the surface vanadia species does not appear to significantly affect the reacti vity of the supported vanadia catalysts for ethane oxidation. (C) 1999 Acad emic Press.