A simple statistical model for V2O5 catalysis

In this work we propose a model to describe the selective oxidation of hydrocarbons at the surface of the V2O5 catalyst. The main ingredients of the model are the concentration of vanadium active sites, the surface and bulk diffusion rates of oxygen vacancies and the probability rate of a hydrocarbon reaction. The reactions take place at the free V2O5 (0 1 0) surface, and the diffusion of vacancies occur along the [0 1 0] (bulk) and [0 0 1] (surface) directions. The coupling between V2O5 and a given metal oxide support determines the concentration of the active vanadium sites, where the reactions can occur. Only the oxygen atoms, which are coordinated to three vanadium sites, take part of the oxidation process. In our calculations we employed two different approaches, single site and pair approximations, and some Monte Carlo simulations. We have found the dependence of the critical concentration of vacancies on the diffusion rates, probability of reaction, and fraction of active vanadium sites, for the catalyst to operate in an active steady state.