Energy of Oxygen-Vacancy Formation on Oxide Surfaces: Role of the Spatial Distribution

Oxygen vacancy formation energies are often used as a descriptor of the catalytic activity of metal oxides for oxidation reactions having the Mars-van Krevelen mechanism. When these energies are calculated, it is often assumed that they depend only on the concentration of the vacancies in the top oxygen layer. Previous work has shown that in the case of TiO2 and V2O5, the energy of vacancy formation depends not only on their concentration but also on the manner in which they are distributed on the surface. However, the energy change due to the change of configuration in these systems is very small. Here, we find that in the case of alpha-MoO3(010) the dependence on the energy of vacancy formation of the distribution of vacancies is very large: if the lattice made by the vacancies consists of parallelograms, the energy of vacancy formation is 0.4 eV smaller than when the lattice consists of rectangles (the two systems having the same vacancy concentration).