Effects of loaded metal on structure and photocatalytic performance of photocatalyst for MAA synthesis from propylene and carbon dioxide

M/MoO_3-TiO_2 (M=Pd, Cu, Ni, Ag) photocatalysts were prepared by sol-gel and impregnation-reaction method. The surface structure, adsorption property, photo absorption performance and photo catalytic performance of M/MoO_3-TiO_2 catalysts were characterized by XRD, TPR, IR, TPD, UV-VisDRS and photoreaction techniques. The experiment results showed that the supported metallic M (M=Pd, Cu) on coupled semiconductor MoO_3-TiO_2 restrains TiO_2 transformation from anatase to rutile and improves the transformation from the tetrahedrally coordinated Mo oxide species to the octahedrally coordinated Mo oxide species. The blue shifting of photo absorption edge and increasing of the photo absorption capacity to visible light were observed clearly after the addition of metallic M (M=Pd, Cu, Ag) on the surface of MoO_3-TiO_2. The photo absorption decreases in the order of Pd/MoO_3-TiO_2, Cu/MoO_3-TiO_2, Ag/MoO_3-TiO_2 and Ni/MoO_3-TiO_2. It can be concluded that the adsorption of CO_2 on Pd/MoO_3-TiO_2 is very strong, and its desorption temperature of horizontal adsorption state increases, thus its photo quantum efficiency is lower than that of Cu/MoO_3-TiO_2 , on which desorption temperature for both CO_2 and C_3H_6 is about the same. Loaded metallic Cu realizes “photo-surface-thermal” synergistic effects and improves photo quantum yield.