Vanadia Aggregates on an Ultrathin Aluminum Oxide Film on NiAl(110)

We model vanadia species of varying sizes and compositions supported on an ultrathin aluminum oxide film on NiAl(110), using density functional theory and statistical thermodynamics. Under typical reducing conditions (UHV, 800 K), the stable species anchor at the support via V−O(2)(−Al) bonds, are vanadyl-terminated, and have the tendency to form islands, growing in height rather than wetting the film. The stretching of the V−O(2)(−Al) interface bonds gives rise to IR active vibration in the 900−960 cm−1 range, in agreement with experiment (945 cm−1). Using the oxygen defect formation energy as a reactivity descriptor, we discuss possible effects of vanadia loading and of the support structure in Mars−van Krevelen-type oxidation reactions. We compare the thin film with the α- and κ-alumina supports.