Highly Selective Oxidative Dehydrogenation of Propane to Propylene over VOx–SiO2 Catalysts

Abstract

To avoid combustion of propane and/or propylene and to obtain high propylene selectivity, oxidative dehydrogenation of propane (ODHP) was carried out using the lattice oxygen of metal oxides in the absence of gas-phase oxygen. This paper summarized the results of our recent attempts to develop new concept and effective catalysts for ODHP. As metal oxides V2O5 was active for ODHP, especially isolated VO4 3− species were active and selective catalysts. The isolated VO4 3− species loaded on a moderate surface area SiO2 and the isolated VO4 3− species into SiO2 framework catalyst exhibited very high propylene selectivities in ODHP. Also, the mechanism of the formation of the isolated VOx species into SiO2 framework catalyst was studied by instrumental analyses. To obtain isolated VO4 3− species in the silica framework, alkoxy-exchange rates between (Si(OC2H5)4 and V(Ot-Bu)3O with PEG is of crucial importance. Isolated VO4 3− was dispersed in the silica framework of catalysts, when the catalysts were prepared with the higher degree of polymerization (over 10) of PEG and the lower vanadium contents (below 1.0 mmol/g-SiO2). During ODHP, lattice oxygen of isolated VO4 3− species was consumed to give propylene and water, was reduced to isolated V3+ species. Therefore regeneration of reduced isolated V3+ species with air is indispensable, and the performance was maintained for at least ten repeated cycles, suggesting that VOx–SiO2 would be a promising catalyst for ODHP.