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 H ₂-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 VO_x 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.