Reaction path analysis of propane selective oxidation over V ₂O ₅ and V ₂O ₅/TiO ₂

The selective oxidation of propane on the vanadyl and bridging oxygen sites of the fully oxidized (0 0 1) V ₂O ₅ surface and of an epitaxial vanadia monolayer supported on (0 0 1) TiO ₂ anatase is analysed using periodic density functional theory (DFT). Both the oxidative dehydrogenation leading to propene and the formation of oxygenated products, namely n-propanol, i-propanol, propanal and acetone, are investigated. Selective oxidation proceeds via a Mars-van Krevelen redox mechanism, and its elementary steps on the vanadia surface are identified. Propane chemisorption preferentially occurs through a secondary CH bond activation via a direct hydrogen abstraction by a lattice oxygen. Supporting a vanadia monolayer on titania strongly enhances the CH bond activation as compared to unsupported V ₂O ₅, yielding a lower activation energy and a more exothermic propane chemisorption. In accordance with experimental observations, the calculations show that the titania support not only modifies the activity of the vanadia monolayer but it also affects the selectivity of the catalyst, favouring the formation of propene compared to the formation of i-propanol and acetone. The vanadyl oxygen is overall the most active site on V ₂O ₅ and V ₂O ₅/TiO ₂, while the bridging oxygen is more selective towards propane dehydrogenation.