Structure and catalytic properties of vanadium oxide supported on mesocellulous silica foams (MCF) for the oxidative dehydrogenation of propane to propylene

A series of vanadium containing mesocellular silica foams (MCF) featuring a well-defined three-dimensional (3D) mesoporosity with ultralarge mesopores were studied with regard to their performance in the oxidative dehydrogenation (ODH) of propane. Catalysts supported on two-dimensional hexagonally ordered siliceous SBA-15 and MCM-41, as well as conventional amorphous silica, were also examined. The dispersity and the nature of the vanadium oxide species were characterized by means of DRIFTS, Raman spectroscopy, DR UV–vis, and H2-TPR. Textural, SAXS, and TEM results indicate that the characteristic mesocellular structural features of MCFs are preserved after the vanadium incorporation. Spectroscopic measurements show that vanadium exists mainly in a tetrahedral environment in dehydrated V-MCF catalysts with V content <4.2 wt%, indicating that a very high surface concentration of isolated or low-polymeric VOx species could be achieved on the present V-MCF systems. The MCF-supported vanadia catalysts exhibit much higher propane conversion and propylene productivity than their conventional V-SBA, V-MCM, and V–SiO2 counterparts in the ODH of propane, demonstrating that apart from the active redox sites, internal molecular transport in mesopores of the catalyst also plays an important role in the gas-phase selective oxidation reactions.