Configurations of V⁴⁺ centers in the MoVO catalyst material. A systematic stability analysis of DFT results

The reactivity of a catalyst is in part determined by its geometric and electronic structure. Here we present a model that is able to describe the energy trend of the important oxidation catalyst material MoVO, as obtained from hybrid density functional calculations for various V⁴⁺/V⁵⁺ configurations. For an exemplary V/Mo occupancy, we systematically examined the universe of all V⁴⁺ distributions. The distribution of these V⁴⁺ centers, in combination with the induced lattice distortions, plays a key role in determining the stability of the material, entailing energy variations of up to ~140 kJ mol⁻¹ per unit cell. Hence, for this kind of catalyst, it is crucial to account for the V⁴⁺ distributions. To this end, we are proposing novel predictive models based on features like the number of Mo centers with two reduced neighbors V⁴⁺ and the locations of potentially reducible centers V⁵⁺. For the V/Mo occupancy chosen, these models are able to describe the energy variation due to the V⁴⁺ distribution with root mean square errors as low as 6 kJ mol⁻¹. Accordingly, catalytically selective sites featuring pentameric units with a single polaron center are among the most of stable configurations. Another aspect of this work is to understand energy contributions of polaron arrangements bracketing Mo centers.