Oxidative dehydrogenation of propane over vanadium and niobium oxides supported catalysts

The oxidative dehydrogenation of propane over niobium and vanadium oxides s upported on high surface area TiO2 has been studied. The two different oxid es have been investigated both as single and mixed supported phase. The van adium containing catalysts are very active but poorly selective to propylen e, while the presence of niobium increases the catalyst performances at low V/Nb ratio. Redox and acid properties of the catalysts have been investiga ted by isopropyl alcohol decomposition test. Results showed that strong aci dity is associated with vanadia and niobia if present as single supported o xide, The interaction between vanadium and niobium leads to the formation o f weaker acid centers. The presence of redox and acid sites at the same tim e is necessary for propane activation. At the same propane conversion, the selectivity to propylene increases when niobium, at a high coverage, is ass ociated to vanadium with low coverage, while it decreases when associated t o higher coverage of vanadium. This has been explained by differences in th e 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 sensi tive to the structure of the catalyst for ethane oxidative dehydrogenation. (C) 1999 Elsevier Science B.V. All rights reserved.