Theoretical study of the effect of (001) TiO₂ anatase support on V₂O₅

The effect of (001) TiO₂ anatase support on the electronic and catalytic properties of a V₂O₅ monolayer is analyzed using density functional theory (DFT). The catalyst is represented by both clusters and periodic slabs. Using two experimentally relevant models of monolayer V ₂O₅/TiO₂ (anatase) catalyst, both weak and strong interactions between a V₂O₅ monolayer and the TiO₂ support have been investigated. In the first model, where a crystallographic (001) V₂O₅ layer is placed on top of the (001) TiO₂ support, the weak interaction between vanadia and titania does not result in a major reconstruction of the active phase. Nevertheless, the changes in the electronic properties of the system are evident. The deposition of the vanadia monolayer on the titania substrate results in charge redistribution, enhancing the Lewis acidity of vanadium and the chemical hardness above the vanadyl oxygen, and in a shift of the Fermi level to lower binding energies accompanied by a reduction in the band gap. In the second model, where the (001) titania anatase structure is extended with a VO ₂ film terminated by half a monolayer of vanadyl oxygen, apart from a similar electronic effect, the strong interaction of the vanadia phase with the titania support resulting from a high order of epitaxy has an important effect on the structure of the active phase. Atomic hydrogen adsorption is most favorable on the vanadyl oxygen of all the investigated surfaces, while the adsorption energy on this site increases by ∼10 kJ/mol due to the weak interaction between vanadia and titania and is further increased by ∼50 kJ/mol as a stronger interaction between the two phases is achieved, all in agreement with the increase in the negative electrostatic potential above the vanadyl site. The observed trends in the reactivity of the oxygen sites in H adsorption for the different catalyst models are successfully explained in terms of a frontier orbital analysis.