Dynamic states of V2O5 supported on SnO2/SiO2 and CeO2/SiO2 mixed-oxide catalysts during methanol oxidation

A series of V2O5 supported on the SnO2/SiO2 and CeO2/SiO2 mixed oxides were investigated during methanol oxidation by in situ Raman spectroscopy, and the catalytic properties of these catalysts were probed by methanol oxidation kinetic studies. The Raman studies revealed that tin oxide forms a surface SnOx overlayer on the silica surface owing to the absence of Raman features of the SnO2 crystallite, but cerium oxide forms bulk CeO2 particles on the silica surface. The impregnated vanadium oxide formed a surface vanadia overlayer on all the catalysts owing to the absence of V2O5 crystallite Raman features. In situ Raman studies of the V2O5/SnO2/SiO2 and V2O5/CeO2/SiO2 catalysts during methanol oxidation indicate that the formation of the VOx-SnOx and VOx-CeO2 interactions totally blocks the formation of surface V-OCH3 groups, which are observed in the V2O5/SiO2 catalysts. The interaction between the surface VOx and the surface SnOx overlayer on silica increases the methanol oxidation reactivity by 1-2 orders of magnitude relative to V2O5/SiO2, and partial interaction between the surface VOx and bulk CeO2 particles increases the methanol oxidation reactivity by 0-1 order of magnitude relative to V2O5/SiO2. Temperature programmed reduction (TPR) studies indicate that the reducibility of the surface vanadium oxide species is dependent on the reducibility of the specific oxide support and confirm the formation of the VOx-SnOx bonds for the V2O5/SnO2/SiO2 catalyst and the formation of VOx-CeO2 as well as VOx-SiO2 bonds for the V(2)O5(/)CeO(2)/SiO2 catalyst.