氨铜比对蒸氨法Cu/SiO_2催化剂活性组分演变及二氧化碳加氢性能的影响

Effect of ammonia-copper ratio on the structural evolution and catalytic activity of Cu/SiO_2 catalysts prepared by ammonia evaporation method in CO_2 hydrogenation reaction

铜催化剂表面铜活性物种的性质与分散度是影响CO_2加氢性能的关键因素。以硅溶胶为载体、铜氨络合物为铜源采用蒸氨法制备了Cu/SiO_2催化剂考察了氨铜比对Cu/SiO_2催化剂表面铜活性物种的形成和CO_2加氢制甲醇反应性能的影响。通过N_2-physisorption、TEM、XRD、IR和BET等技术对催化剂的结构和性质进行了表征。结果显示,铜氨溶液中适当的氨浓度,有利于铜氨配体的形成和蒸氨过程中铜活性组分的均匀分布,有利于层状硅酸铜和氧化铜双活性组分的形成。在反应温度523 K,反应压力2.5 MPa,进气比V(CO_2):V(H_2):V(N_2)=10:30:4,反应空速1800 mL_(STP)/(g·h)的条件下,氨铜比为4的Cu/SiO_2-N4催化剂获得较优CO_2加氢催化性能,CO_2的转化率31%,CH_3OH的选择性54.8%,CH_3OH的收率17%。

The nature and distribution of surface copper active species on the copper based catalysts are crucial for the catalytic hydrogenation of CO 2 to methanol .Silica supported copper catalyst Cu /SiO2 was pre-pared by ammonia evaporation （ AE） method with different ammonia-copper molar ratio and characterized by N2-physisorption ,TEM,XRD,IR and BET techniques .Performance of the Cu/SiO2 catalysts on the hy-drogenation of CO2 reaction was also evaluated with a feed gas ratio of V（CO2）∶V（H2）∶V（N2）=10∶30∶4 under 523 K,2.5 MPa.The results indicated that the ammonia-copper molar ratio in the AE method exerted profound effects on the copper loading ,texture properties and surface composition of the Cu /SiO2 catalysts. Catalysts with the proper copper loading ,smaller copper particle size ,larger metallic copper surface area and good dispersion of copper species could be obtained by using a proper ammonia -copper molar ratio .The Cu/SiO2-N4 catalyst with an optimal ratio of ammonia to copper of 4 can achieve CO 2 conversion of 31%,CH3 OH selectivity of 54.8%and CH3 OH yield of 17%under the above condition .