Reactivity of the Oxygen Sites in the V2O5/TiO2 Anatase Catalyst

We present for the first time a theoretical investigation on the reactivity of the different oxygen sites in a dispersed V 2 O 5 /TiO 2 slab model. Our model represents anhydrous conditions and contains all the potentially active oxygen sites proposed to date in the literature: vanadyl V O, bridging V−O−V, interface V−O−Ti, and surface Ti−O−Ti oxygen sites. Geometric features are analyzed in terms of bond distances and site accessibility. Projected density of states diagrams show a decrease of the band gap for the supported system with respect to pure anatase (001). The most energetic levels of the valence band correspond to the oxygen atoms in the V 2 O 5 unit, although a further decomposition in terms of mono- and dicoordinated oxygen is not obvious. Atomic hydrogen adsorption on the different sites is tracked. The most exothermic systems are those where H adsorbs on the V 2 O 5 oxygen sites due to their higher basicity regarding pure anatase. The heats of adsorption referred to atomic H are V−O−Ti (2.95 eV) > V O (2.60 eV) > V−O−V (2.17 eV) > Ti−O−Ti (2.07 eV). This means that the most reactive sites are those located at the interface between the V 2 O 5 and the TiO 2 unit, while the vanadyl V O bonds are more stable and would react at a lower extent in hydrogen atomic adsorption. Relaxation makes the adsorption energy decrease: the support relaxes less when hydrogen adsorbs than for the bare V 2 O 5 /TiO 2 system. H adsorption forms hydroxyl OH bonds by reduction of the vanadium atom, even when the adsorption site is located on the TiO 2 surface sites.