二氧化碳加氢直接合成二甲醚催化剂的研究 Ⅱ 铜/锌对复合催化剂结构和性能的影响

In order to systemically investigate the effects of Cu/Zn ratio on physical-chemical properties and catalytic performance of catalyst, a series of CuO-ZnO-Al2O3/HZSM-5 composite catalysts with different Cu/Zn ratios (Cu/Zn=1/2；4/5；5/4 and 2/1, weight ratio of oxides) were prepared. And their catalytic performance for hydrogenation of CO2 was evaluated in a laboratory fixed-bed reactor system. The physical-chemical properties of these catalyst samples were also studied by means of H2-TPR, XRD, BET, IR and XPS. The results showed that Cu/Zn ratio in catalyst could affect the catalytic activity, the crystal phase structure and the reduction property of the catalyst to a certain extent. Among the concerned catalysts with different Cu/Zn ratios, the catalyst with Cu/Zn=1/2 showed better catalytic performance for dimethyl ether and methanol synthesis. The TPR profiles of different catalysts showed some difference. With the increase of Cu content, the areas of the reduction peaks increased and the reductive peak temperature decreased slightly. The XRD results indicated that the degree of copper dispersion was decreased with the increase of Cu content in the catalysts. There was no evident difference between the catalysts in BET specific surface areas, and there was also no obvious relation between BET specific surface area and catalytic performance. The IR results of the catalysts presented that there was a corresponding relation between the catalytic activity and the intensity of absorption peak at 1 101 cm-1, which indicated the interaction between the metal oxides and HZSM-5. The XPS characterization proved that the active sites could be in two forms, i.e., Cu+ and Cu0, which supported the viewpoint that the Cu+ and Cu0 both were active species during methanol synthesis.