Oxidative dehydrogenation of propane over vanadium and niobium oxides supported catalysts

The oxidative dehydrogenation of propane over niobium and vanadium oxides supported on high surface area TiO2 has been studied. The two different oxides have been investigated both as single and mixed supported phase. The vanadium containing catalysts are very active but poorly selective to propylene, while the presence of niobium increases the catalyst performances at low V/Nb ratio. Redox and acid properties of the catalysts have been investigated by isopropyl alcohol decomposition test. Results showed that strong acidity is associated with vanadia and niobia if present as single supported oxide, The interaction between vanadium and niobium leads to the formation of weaker acid centers. The presence of redox and acid sites at the same time is necessary for propane activation. At the same propane conversion, the selectivity to propylene increases when niobium, at a high coverage, is associated to vanadium with low coverage, while it decreases when associated to higher coverage of vanadium. This has been explained by differences in the local environment of vanadium sites with niobium sites at the surface of TiO2. The comparison of the same catalysts for oxidative dehydrogenation of ethane and propane shows that the formation of carbon oxides is more sensitive to the structure of the catalyst for ethane oxidative dehydrogenation. (C) 1999 Elsevier Science B.V. All rights reserved.