Abstract: Photocatalytic synthesis of hydrocarbon oxygenates from CO₂ with hydrocarbons is of great importance to environmental protection, utilization of carbon resources and synthetic chemistry. Adsorption property of CO₂ and C₃H₆ and photo-stimulated surface reaction to synthesize methacrylic acid from CO₂ and C₃H₆ over the coupled semiconductor WO₃-TiO₂ catalyst with metallic Cu supported were studied. The experimental results reveal that the three kinds of active sites exist on the surface of Cu/WO₃-TiO₂ catalyst: Metallic site Cu, Lewis acid sites W⁶⁺ and Ti⁴⁺, Lewis base sites bridge O in W_OTi and terminal O in WO. Chemisorbed CO₂ on the surface of Cu/WO₃-TiO₂ catalyst forms high active horizontal state Cu_COO→Ti⁴⁺(or W⁶⁺) with the synergic action of metallic site Cu and Lewis acid sites Ti⁴⁺(or W⁶⁺), while dual-sites adsorption of β-H and β-C of C₃H₆ which forms state Cu_CH2C(CH₃)_H→OW, is found mainly on the Lewis base-site WO and the metallic site Cu, respectively. Blue-shifting of band edge of the absorption spectra and increasing of the photo absorption capacity on Cu/WO₃-TiO₂ catalyst improve the catalysis property of Cu/WO₃-TiO₂ catalysts. Photo-quantum efficiency of the reaction is the highest among the others, which reaches 19.7%. The selectivity of MAA is over 95% on 1%Cu/10%WO₃-TiO₂ catalyst under the proper reaction conditions(SV=200 h^-1, p=0.1 MPa, T=383 K and P=125 W). Based on the experimental results above, a possible mechanism is proposed for the photo-stimulated surface reaction to synthesize methacrylic acid from CO₂ and C₃H₆ over Cu/WO₃-TiO₂ catalysts.

Key words: Photocatalyst, Carbon dioxide, Propylene, Methacrylic acid, Reaction performance