M/WO₃-TiO₂ (M＝Pd, Cu, Ni, Ag) photocatalysts were prepared by sol-gel and impregna-tion-reaction method. The surface structure, photo absorption performance and photo catalytic performance of M/WO₃-TiO₂ catalysts were characterized by XRD, XPS, TPR, IR, TPD, UV-Vis-DRS and photoreactor techniques. The experiment results showed that the metal supported on coupled semiconductor WO₃-TiO₂ restrained the transformation from anatase TiO₂ to rutile TiO₂. The blue shift of photo absorption edge and increase of the photo absorption capacity to visible light were observed clearly after the addition of metal to WO₃-TiO₂. The photo absorption per-formance was decreased in the order of Pd/WO₃-TiO₂, Cu/WO₃-TiO₂, Ag/WO₃-TiO₂ and Ni/WO₃-TiO₂. It can be concluded from the analysis results that the adsorption capacity of CO₂ on Pd/WO₃-TiO₂ was much stronger than others. Its desorption temperature of horizontal adsorption state was increased, so its photo quantum efficiency became lower. Photo quantum efficiency of Cu/WO₃- TiO₂ was the highest, on which desorption temperature of CO₂ was approximate to C₃H₆. Photo quantum efficiency of the reaction reached 19.7% and the se-lectivity to MAA was over 95% on Cu/WO₃-TiO₂ catalyst under proper reaction conditions: v_s (space velocity) 200 h^－1, pressure 0.1 MPa, temperature 110 ℃ and UV light inten-sity 0.65 mW•cm^－2. Loaded metallic Cu on coupled semiconductor WO₃-TiO₂ realized photo- surface-thermal synergistic effects and improved photo quantum efficiency.

Key words: coupled semiconductor, photo quantum efficiency, carbon dioxide, propylene, methacrylic acid