Study On Photo Stimulated Surface Catalysis Of CH₂=CHCOOH Synthesizing Directly From CO₂ And C₂H₄ Over Cu/ZnO-TiO₂ Catalysts

Direct synthesis of crylic acid from CO2 with C2H4 is important one of the atom-economic reaction, and the technology of photo stimulated surface catalytic reaction (PSSCR) has been used to this reaction system at first time. In this work, a series of Cu/ZnO-TiO2 solid materials were prepared by sol-gel method, and their preparation conditions, chemical composition and surface structure, chemisorption properties, absorptivity of UV light and photoreaction behaviors were investigated by techniques of DTA-TG, TPR, TEM, BET, XRD, IR, UV-vis and PSSCR-GC. The Cu/ZnO-TiO2 solid materials are composed of anatase TiO2, ZnTiO3 and ZnO with particle sizes around 10nm and surface area over 80m2/g, and metallic Cu clusters are dispersed in a high degree on the surface of solid materials. Three kinds of active sites of Lewis acid sites Zn2+ and Ti4+, Lewis base sites surface O- and bridge-O2- and metallic sites Cu appeared on the surface of these solid materials.The ZnO-TiO2 n-p coupled semiconductors can absorb UV light of 250-400 nm effectively with the absorptance over 85%. The absorbance of visible light obviously increase and UV absorbance limit shift to shorter wavelength region after Cu supported on ZnO-TiO2. CO2 can be chemisorbed on the Cu and Lewis acid sites of material surface to form bidentate, bridge and shearing adsorption states, while C2H4 can be chemisorbed on the Cu and Lewis base site to form undissociated intermediate. There exist competitive adsorption between CO2 and C2H4 on Cu.The PSSCR performance is influenced by the content of ZnO in the Cu/ZnO-TiO2 solid materials. The solid material, 1%Cu/20%Zn-TiO2, has the best PSSCR performance and the products are crylic acid, aldehyde and CO. The reaction temperature, space velocity, and reactant component have obvious effects on the PSSCR. IUnder the conditions of radiation of UV light (wavelength 365nm, intensity 10mw/cm2), 100℃, space velocity 200 h-1 and CO2:C2H4=1:1, the conversions of CO2 and C2H4 reache1.25% and 1.23% respectively, and the selectivity to crylic acid is over 90%;Based on the experimental results, a PSSCR mechanism for direct-synthesis of crylic acid from CO2 and C2H4, the action of each component in the solid material and the synergetic effects of "light-surface-thermal" in PSSCR process has been proposed.