V-containing MCM-41 and MCM-48 catalysts for the selective oxidation of propane in gas phase

Well-organised V-containing MCM-41 and -48 (0.3-1 wt.% of V content) have been synthesised by one-pot synthesis or by grafting using VOSO4 or VOCl3 as V sources, respectively. The samples before and after the calcination step have been characterised by several physicochemical techniques (Ar and N-2 adsorption, XRD, diffuse reflectance-UV-VIS (DR-UV-VIS) spectroscopy, temperature-programmed reduction). It was found that V species in the as-prepared catalysts were mainly as vanadyl ions (VO2+), while highly dispersed V5+ species with tetrahedral coordination were observed in the calcined materials. The catalytic behaviour of the calcined materials for the gas phase oxidation of propane has been studied using low propane/oxygen ratios in the 500-550 degreesC temperature range. Also, the catalytic results of V-containing mesoporous materials have been compared to those obtained on SiO2-supported vanadia catalysts with similar vanadia contents. In all cases, propylene, CO and CO2 were the main reaction products although partial oxygenated products (selectivities lower than 10%) were also observed. V-containing MCMs materials show a selectivity to propylene higher than SiO2-supported vanadia catalysts. These results can be explained by taking into account the higher surface area of MCMs materials which allows a better dispersion of V species on the mesoporous supports. (C) 2001 Elsevier Science B.V. All rights reserved.