Oxidative dehydrogenation of ethane and propane over vanadia and molybdena supported catalysts

The catalytic performance of vanadia and molybdena catalysts with monolayer coverage supported on alumina and titania in the oxidative dehydrogenation (ODH) of ethane and propane was investigated. The surface structure of the MO, species (M = Mo, V) was investigated with laser Raman spectroscopy, while the acidity and reducibility of the materials were probed by temperature programmed NH3 desorption and H-2 reduction, respectively. Testing of the materials showed that in both ethane and propane oxidative dehydrogenation, vanadia catalysts were much more active than the molybdena ones, irrespective of the support used. Comparison of the catalysts based on the support used, showed that titania-supported catalysts exhibit superior activity but inferior selectivity than the corresponding alumina-supported ones. Taking into account that the oxygen involved in the M-O-support bonds is kinetically relevant, the behavior of each catalytic system can be explained based on the electronegativity of each cation involved in these bonds. The apparent activation energies for ethane and propane ODH, derived from kinetic measurements, follow the reactivity of the samples. Despite the higher reactivity of propane at same reaction conditions, similar values of activation energy were calculated. The pre-exponential factors could be responsible for the lower reaction rates in ethane ODH. (c) 2005 Elsevier B.V. All rights reserved.