Photodecomposition of NOx on Ag/TiO₂ composite catalysts in a gas phase reactor

With NO as model gas component, photocatalytic NOx decomposition under UV and visible light irradiation has been investigated in a gas phase photocatalytic reactor over anatase TiO₂ and Ag/TiO₂, respectively. TiO₂ and Ag/TiO₂ were prepared by a solvothermal method and characterized by X-ray diffraction (XRD), BET, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) etc. The activity of the photocatalysts was evaluated by decomposition rate of NO and yield of N₂, respectively. It was found that although photodecomposition of NO over pure TiO₂ is very quick, NO has not been converted into N₂ and O₂. It means that some by-products have formed. N₂ formation is a relatively slower process. It was found that the selectivity for photodecomposition of NOx into N₂ can be significantly improved by introducing appropriate amount of Ag into TiO₂. The 1 wt% Ag loaded on TiO₂ showed the highest activity for both NO decomposition and N₂ production. The possible mechanism for the enhancement of photocatalytic activity of anatase Ag/TiO₂ was attributed to the coexistence of Ag⁰ and Ag⁺ on the surface of TiO₂, with a Ag⁺/Ag ratio of ca. 0.86, which played different roles in the photocatalytic process. Our study could be valuable for the development of efficient photocatalyst for NOx photodecomposition with a high selectivity.