Reaction Performance of Cu/V_2O_5-TiO_2 Photocatalyst for Synthesis of MAA from Propylene and Carbon Dioxide

Adsorption property and photo-stimulated surface reaction of CO_2 and C_3H_6 on the loaded metal Cu coupled semiconductor V_2O_5-TiO_2 catalyst was studied by IR、 TPD、 UV-Vis and photo-microreactor techniques. The experimental results pointed out that the three kinds of active sites exist on the surface of the catalysts: Metallic site Cu, Lewis acid sites V~(5+) and Ti~(4+), Lewis base sites bridge O in V-O-Ti and terminal O in V=O. CO_2 chemisorbed on the surface of Cu/V_2O_5-TiO_2 catalyst forms high active horizontal state Cu-(CO)-O→Ti~(4+)(or V~(5+)) with the synergic action of metallic site Cu and Lewis acid sites Ti~(4+) (or V~(5+)), while dual-sites adsorption state of β-H and β-C of C_3H_6, Cu-C(CH_2CH_3)-H→O=V, has been found mainly on the Lewis base-site V=O and the metallic site Cu, respectively. Red-shift of band edge of absorption spectra and increase of the photo absorption capacity on Cu/V_2O_5-TiO_2 catalyst improves catalysis property of Cu/V_2O_5-TiO_2 catalyst. Photo-quantum efficiency of the reaction on 1%Cu/10%V_2O_5-TiO_2 catalyst is highest among the others, which reaches 15.1%, and the selectivity of MAA is over 95% under the proper reaction conditions. Based on the experimental results above, a possible mechanism is proposed for the photo-stimulated surface reaction to synthesize methacrylic acid from CO_2 and C_3H_6 on the Cu/ V_2O_5-TiO_2 catalyst.