Cu/WO_3-TiO_2光催化剂上丙烯和二氧化碳合成MAA反应性能

Photocatalytic Synthesis of MAA from Propylene and Carbon Dioxide over Cu/WO_3-TiO_2 Catalyst

研究了Cu/WO3-TiO2对CO2和C3H6的吸附特性和光催化性能.结果表明,在Cu/WO3-TiO2催化剂表面存在金属位Cu,Lewis酸位W6+和Ti4+以及Lewis碱位W—O—Ti的桥氧和WO的端氧三类活性中心;在金属位Cu和Lewis酸位Ti4+(或W6+)的协同作用下,CO2形成活性较高的卧式吸附态Cu—(CO)—O→Ti4+(或W6+),C3H6的β-H和β-C分别吸附在Lewis碱位WO与金属位Cu上,形成Cu—(CH2)C(CH3)—H→OW吸附态;Cu/WO3-TiO2催化剂吸收阈值蓝移和光吸收量的提高均有利于其催化活性的提高,担载质量分数为10%的WO3光催化剂的催化活性优于其它含量的催化剂,光量子效率最高(19.7%);在383K,0.1MPa,空速200h-1和125W紫外灯辐照下,C3H6转化率为7.4%,甲基丙烯酸(MAA)的选择性超过95%.根据实验结果提出了光促表面催化合成反应的机理.

Photocatalytic synthesis of hydrocarbon oxygenates from CO_2 with hydrocarbons is of great importance to environmental protection, utilization of carbon resources and synthetic chemistry. Adsorption property of CO_2 and C_3H_6 and photo-stimulated surface reaction to synthesize methacrylic acid from CO_2 and C_3H_6 over the coupled semiconductor WO_3-TiO_2 catalyst with metallic Cu supported were studied. The experimental results reveal that the three kinds of active sites exist on the surface of Cu/WO_3-TiO_2 catalyst: Metallic site Cu, Lewis acid sites W^(6+) and Ti^(4+), Lewis base sites bridge O in W\_O\_Ti and terminal O in WO. Chemisorbed CO_2 on the surface of Cu/WO_3-TiO_2 catalyst forms high active horizontal state Cu\_(CO)\_O→Ti^(4+)(or W^(6+)) with the synergic action of metallic site Cu and Lewis acid sites Ti^(4+)(or W^(6+)), while dual-sites adsorption of β-H and β-C of C_3H_6 which forms state Cu\_(CH_2)C(CH_3)\_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/WO_3-TiO_2 catalyst improve the catalysis property of Cu/WO_3-TiO_2 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%WO_3-TiO_2 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 CO_2 and C_3H_6 over Cu/WO_3-TiO_2 catalysts.