Vanadium Oxide Supported on Mesoporous MCM-41 as Selective Catalysts in the Oxidative Dehydrogenation of Alkanes

Abstract

The application of different techniques (51V NMR, diffuse reflectance, and TPR-H2) in the characterization of vanadia supported on mesoporous MCM-41 catalysts shows that the nature of the vanadium species depends on the V loading. In dehydrated catalysts with V content lower than 7 wt%, vanadium is mainly in a tetrahedral environment. In the presence of moisture, most V5+, placed in accessible positions, binds to water molecules, becoming hexacoordinated, while some V5+ species, probably located within the pore walls, keep their tetrahedral coordination. Higher V contents in the catalyst leads to the formation of polymeric V2O5-like species. Both XRD and textural results indicate that the mesoporous structure of the support is mostly maintained after the vanadium incorporation, and therefore high surface areas were obtained on the final catalysts. MCM-41-suppported vanadia catalysts are active and selective in the oxidative dehydrogenation of propane and ethane, although the catalytic behavior depends on the V loading. A high rate of formation of propylene or ethylene per unit mass of catalyst per unit time have also been observed as a consequence of the high dispersion of V atoms achieved on the surface of the support.