The oxygen-assisted transformation of propane to CO x/H 2 through combined oxidation and WGS reactions catalyzed by vanadium oxide-based catalysts

Abstract

This paper reports about the gas-phase oxidation of propane catalyzed by bulk vanadium oxide and by alumina- and silica-supported vanadium oxide. The reaction was studied with the aim of finding conditions at which the formation of H 2 and CO 2 is preferred over that of CO, H 2O and of products of alkane partial oxidation. It was found that with bulk V 2O 5 considerable amounts of H 2 are produced above 400 °C, the temperature at which the limiting reactant, oxygen, is totally consumed. The formation of H 2 derived from the combination of: (i) oxidation reactions, with generation of CO, CO 2, oxygenates (mainly acetic acid), propylene and H 2O, all occurring in the fraction of catalytic bed that operated in the presence of gas-phase oxygen, and (ii) WGS reaction, propane dehydrogenation and coke formation, that instead occurred in the fraction of bed operating under anaerobic conditions. This combination of different reactions in a single catalytic bed was possible because of the reduction of V 2O 5 to V 2O 3 at high temperature, in the absence of gas-phase oxygen. In fact, vanadium sesquioxide was found to be an effective catalyst for the WGS, while V 2O 5 was inactive in this reaction. The same combination of reactions was not possible when vanadium oxide was supported over high-surface area silica or alumina; this was attributed to the fact that in these catalysts vanadium was not reduced below the oxidation state V 4+, even under reaction conditions leading to total oxygen conversion. In consequence, these catalysts produced less H 2 than bulk vanadium oxide.