(545c) Oxidative Dehydrogenation of Ethane and Propane By CO2
The vanadia silica catalysts at sub-monolayer VOx coverage were found to be active and selective in propane ODH by O2 and CO2, while VOx multilayers and nano-sized clusters showed lower activity and selectivity. Moreover, due to its acidic character of silica, it showed undesirable carbon deposition (coking) in propane ODH by CO2 in a short period of reaction time and as a result catalyst deactivated quickly. Around 20 % weight loss observed for the used catalyst after 30 hours propane ODH by CO2 reaction under conditions of TGA in air. On the other hand, the same catalyst employed to propane ODH by O2, almost no carbon deposition was observed. Our experimental observations are in agreement with recent theoretical calculations indicating that in this catalytic system, carbon deposition is thermodynamically favorable, unless the surface character is modified by basic additives, such as Na+. Moreover, basic additives were recently reported to enhance the monolayer coverage of VOx species on silica which also improved their activity and selectivity in propane ODH by CO2.
The catalytic activity of these species may be optimized by varying the surface coverage of VOx species and the nature of the support and promoters.