Deactivation mechanism of PtO_x/TiO_2 photocatalyst towards the oxidation of NO in gas phase

摘要

This study has been undertaken to investigate the roles of PtO and PtO_2 deposits in photocatalytic oxidation of NO over Pt-modified TiO_2 catalysts. These photocatalysts were prepared by neutralization method and characterized by XRD, BET, XPS, TEM and FTIR. It was found that Pt dopant existed as PtO and PtO_2 particles in as-prepared photocatalysts. And these Pt dopants would change their oxidation states during the photocatalytic oxidation reaction. An in situ XPS study indicated that a portion of PtO_2on the surface of Pt/TiO_2 was reduced to PtO under UV irradiation. The migration of electrons to PtO_2 particles could separate the electrons and holes, resulting in the improvement of photocatalytic activity. And the depletion of PtO_2by electrons could lead to the deactivation of Pt/TiO_2 catalyst. Moreover, PtO particles could be corroded to form Pt~(2+) ions by HNO_2, which was one of the products of photocatalytic oxidation of NO. NO would adsorb on Pt~(2+) related sites to form Pt~(n+)-NO nitrosyls, retarding photocatalytic oxidation of NO to NO_2.