Abstract
On the surface: Adsorption of O~2~ at the surface oxygen vacancy (SOV) sites of TiO~2~ reconstructs the lattice oxygen (healing SOVs), resulting in a decrease of the photocatalytic activity of oxidizing CO over vacuumβpretreated TiO~2~ with increasing temperature (see scheme). Adsorption of H~2~ produces new SOVs at the TiO~2~ surface and stabilizes the photocatalytic activity.magnified image
Photocatalytic oxidation of CO over vacuumβpretreated TiO~2~ is performed in a series of systems with the introduction of O~2~, CO, and H~2~ in different orders. The photocatalytic oxidation of CO is dependent on the order of introduction of O~2~, CO, or H~2~, and introducing O~2~ prior to CO promotes the oxidation of CO. Moreover, an increase of reaction temperature suppresses the oxidation of CO, but the preintroduction of H~2~ reduces this suppression effect. The results of the chemisorption of O~2~, CO, and H~2~ at the TiO~2~ surface reveal that the adsorbed O~2~ heals the surface oxygen vacancy (SOV) sites of TiO~2~, while the adsorbed CO and H~2~ promote the formation of new SOVs. It is proposed that changes in the amounts of adsorbed O~2~ and SOVs are mainly responsible for the differences of CO conversion in different systems.