Reactivity of a reduced metal oxide surface: hydrogen, water and carbon monoxide adsorption on oxygen defective rutile TiO2(1 1 0)

The reactivity at reduced surface differs from that on the stoichiometric perfect surfaces. This does not originate uniquely from the modification of the coordination; electron count also is determining. The general trend is a decrease of the heat of adsorption on the metal cations. The reactivity decreases at sites in the vicinity of the defects due to the reduction induced by the O vacancies. At the defect site the decrease is less pronounced for H, H2, CO and molecular H2O. In the case of H2O dissociative adsorption, the defect site is more reactive than the perfect surface. Thus, a hydration converting the defective-reduced TiO2 to the hydrogenated non-defective-reduced surface is easy. The resulting structure possesses surface hydroxyl groups. It is probably the easiest way to form the hydrogenated non-defective surface. On TiO2, the defective surface requires very anhydrous conditions.