Chemical nature of point defects at the (VO)2P2O7(1 0 0) surface

Generally, the chemistry of VPO-based catalysts is controlled by the properties of surface defects. Therefore, the effect of isolated vacancies on the reactivity of vanadyl pyrophosphate, the main component of VPO catalysts, seems to be a natural starting point for a theoretical analysis to understand better the real material. Here, we report density functional calculations of the electronic structure for different clusters modeling the defective (VO)2P2O7(1 0 0) surface, where a neutral oxygen monovacancy is incorporated. This study is complementary to our previous investigations on the energetics and the Lِwdin charge analysis of the same type of defects. The electronic structure of the defective (1 0 0) surface is discussed by means of the total and atomic (partial) density of states to show modifications of the electronic states caused by the differently located vacancies. A theoretical estimation of the density of states reveals evidence for the presence of color center-induced levels for high-coordinated vacant sites and their absence in the case of low-coordinated vacancies. It is shown that only in the case of high-coordinated oxygen vacancies the band gap is reduced relative to the clean surface. Specific features of the density of states projected onto different cationic and anionic surface sites agree with experimental evidence on their implications for catalytic performance.