Enhanced Oxidation Reactivity of WO3(001) Surface through the Formation of Oxygen Radical Centers

The gamma-WO3(001) surfaces doped by a series of group VB elements have been investigated by means of first-principles density functional theory (DFT) calculations doping of VB element is preferential under O-rich growth conditions and that the replacement of tungsten by Ta atom is energetically favorable among three group VB elements. The introduction of a group VB atom into the surface results in the downward shift of the Fermi level, and in most cases, the 2p states derived from the in-plane oxygen atom are still the dominate components at the Fermi level as before doping. However, the substitution of Ta dopant for 6-fold-coordinated tungsten atom (W-6f) at the top layer is a special case in which the 2p states of the top terminal oxygen atom just above Ta become the primary compositions at the Fermi level. Only in this model, the spin densities are mainly located on the terminal oxygen atoms near the Ta site, and the oxygen radical center observed in the gas-phase W3O9+ cluster is reproduced. Therefore, the formation of radical oxygen center in the condensed phase depends on not only the substituent site but also the type of the dopant. Moreover, additional calculations are performed to study the oxidation reaction of CO molecule on the above Ta doped surface, and results indicate that the energy barrier for CO oxidization is obviously reduced compared to the undoped one, which implies that the introduction of Ta at W-6f site can efficiently improve the oxidation reactivity of the WO3(001) surface.