Deactivation mechanism of PtOx/TiO(2) photocatalyst towards the oxidation of NO in gas phase.

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(2) on 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(2) by electrons could lead to the deactivation of Pt/TiO(2) catalyst. Moreover, PtO particles could be corroded to form Pt(2+) ions by HNO(3), 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).