Deactivation mechanism of PtOx/TiO2 photocatalyst towards the oxidation of NO in gas phase

This study has been undertaken to investigate the roles of PtO and PtO2 deposits in photocatalytic oxidation of NO over Pt-modified TiO2 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 PtO2 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 PtO2 on the surface of Pt/TiO2 was reduced to PtO under UV irradiation. The migration of electrons to PtO2 particles could separate the electrons and holes, resulting in the improvement of photocatalytic activity. And the depletion of PtO2 by electrons could lead to the deactivation of Pt/TiO2 catalyst. Moreover, PtO particles could be corroded to form Pt2+ ions by HNO3, which was one of the products of photocatalytic oxidation of NO. NO would adsorb on Pt2+ related sites to form Ptn+–NO nitrosyls, retarding photocatalytic oxidation of NO to NO2.