CO_2加氢直接合成二甲醚催化剂的研究——沉淀方法对复合催化剂性能的影响

Study on Direct Synthesis of Dimethyl Ether by Hydrogenation of Carbon Dioxide——Effects of Co-Precipitation Method on Structure and Properties of Catalysts

分别采用三种不同的共沉淀方法(一步法、两级法和两步法)制备了 CuO-ZnO-Al_2O_3/HZSM-5复合催化剂。对 CO_2加氢直接合成二甲醚的催化活性顺序(自高至低)依次为:两步法催化剂>两级法催化剂>一步法催化剂。X 射线衍射(XRD)表征结果表明,采用两步共沉淀法时,催化剂的前驱体中有类水滑石[Cu_2Zn_4Al_2(OH)_(16)CO_3·4H_2O]结构的 Cu-Zn-Al 三元物相生成,焙烧后的催化剂中 CuO 和 ZnO的相互分散程度较好,Cu 和 Zn 物种之间相互作用程度较强,有利于催化剂活性的发挥。红外光谱(IR)研究发现,催化剂在1 101 cm^(-1)和450 cm^(-1)处的 IR 吸收峰强度,可表现 Cu/Zn/Al 氧化物与 HZSM-5之间相互作用程度,且与催化剂的活性之间存在着对应关系。

Three composite catalyst samples （CuO-ZnO-AlO3/HZSM-5） were prepared with different co-precipitation methods, i. e., one-step method, two-stage method and two-step method. The activity evaluation data on direct synthesis of dimethyl ether by CO2 hydrogenation indicated that their activity in sequence was： two-step method was the best, two-stage method was in middle, and both were better than one-step method. The XRD characterization showed that there existed the Cu-Zn-Al ternary phase with the hydrotalcite-like structure [Cu2Zn4Al2 （OH）,6COa · 4H2O] in the catalyst precursor prepared by two-step method, and the CuO and ZnO in the calcined catalyst sample were of better degree of dispersion, stronger interaction between the Cu and Zn species, which might contribute to the better catalytic activity. IR results indicated that the intensity of absorption peaks positioned at the wave numbers of 1 101 cm^-1 and 450 cm^-1 for catalyst could express the degree of interaction between the metal oxide component and the HZSM-5 zeolite component, and might be related to its catalytic activity.