DFT investigation into the experimentally observed influence of oxide support in the ODH of propane over supported vanadia catalysts

Oxidative dehydrogenation (ODH) of propane on the supported vanadia catalysts is studied experimentally and by periodic density functional theory (DFT) calculations. About half monolayer of vanadia supported over amorphous silica, gamma-alumina and anatase titania are prepared and characterized by Raman spectroscopy. Typical peaks due to the presence of molecularly dispersed species are detected. The ODH activity of these catalysts showed that titania is a better oxide support than alumina, which is even better than silica. Among the different surface vanadia species possible, a monomeric VO4 species is modeled on periodic surfaces of amorphous silica, gamma-alumina, and anatase titania and the structure was validated by comparing the calculated V=O stretch with the experimentally measured value. Theoretical analysis using DFT over the modeled catalysts provided mechanistic insights into the activity trend of the supported vanadia catalysts for the ODH activity. Specific attention is given to understand the effect of the oxide support. Comparison of the rate determining step on these modeled catalysts suggested that titania is a better oxide support for this reaction, which is consistent with the experimentally observed trends in the turnover frequency values of propane. Furthermore, the mechanism over titania and alumina supported vanadia catalysts are similar and involve bridging oxygen, whereas terminal oxygen is more favorable for silica supported vanadia catalysts.