Theoretical and Experimental Study of Light Hydrocarbon Ammoxidation and Oxidative Dehydrogenation on (110)-VSbO4 Surfaces

Abstract

Density Functional Theory (DFT) calculations have been performed for ethane, ethylene, propane, and propylene adsorption on the rutile VSbO4 structure to uncover the reaction mechanism during both ODH and ammoxidation reactions. This study is complementary to a previous paper in which the adsorption of ammonia on this structure was deeply analyzed, and in addition, experimental activity results for both reactions are shown to complete the theoretical DFT calculations. These results show that ammonia, ethane, and ethylene compete for the same active sites, the former adsorbing strongly. This explains why this catalytic system is not active for ethane ammoxidation; the presence of ammonia blocks the other molecule adsorption sites and prevents ethane oxidative dehydrogenation to ethylene. Such competition does not occur with propane or propene since the adsorption of both ammonia and hydrocarbon is possible at different sites, explaining why this catalytic system is active for propane ODH reaction. During ammoxidation, molecularly dispersed VOx species are able to transform the propane molecule into propylene. Then, intermediate propylene can coadsorb along with ammonia on the trirutile VSbO4, inserting the nitrogen atom that forms acrylonitrile. Calculations show that the adsorptions studied are more favored when the rutile structure presents a cationic vacancy.