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

摘要

A series of vanadium containing mesocellular silica foams (MCF) featuring a well-defined three-dimensional (3D) mesoporosity with ul-tralarge 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 dis-persity 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 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-SiO_2 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.