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

Reactivity of a Reduced Metal Oxide Surface - Hydrogen, Water and Carbon Monoxide Adsorption on Oxygen Defective Rutile TiO2(110). Menetrey, M., Markovits, A., Minot, C.: Surface Science, 2003, 524[1-3], 49-62