Influence of secondary metal oxide additives on molecular structure and reactivity of V2O5/SnO2/SiO2 catalysts during methanol oxidation

Abstract

In situ Raman studies of the CrO3, Nb2O5, and WO3-V2O5/SnO2/SiO2 catalysts have revealed that chromium oxide forms a surface CrO3 overlayer and niobium oxide and tungsten oxide form bulk Nb2O5 and WO3 particles, respectively, on the surface. The interaction of the surface CrO3 species with the V-O-Sn bridging bond in the V2O5/SnO2/SiO2 catalyst induces the total reduction of the surface vanadium oxide species during methanol oxidation. The absence of V+5 atom in the catalyst during reaction conditions results in a lower reactivity of the methanol oxidation reaction. The formation of bulk Nb2O5 and WO3 particles on the V2O5/SnO2/SiO2 surface also decrease methanol oxidation reactivity. The formation of new surface acid sites on the promoted-V2O5/SnO2/SiO2 catalysts does not alter the reaction mechanisms toward the acid site's product (CH3OCH3), and only one site (redox) is needed to perform the methanol oxidation reaction. TPR studies indicate that the reducibility of the surface vanadium oxide species is affected by the reducibility of the secondary metal oxide.