二氧化碳加氢直接合成二甲醚催化剂的研究——沉淀次序对复合催化剂结构和性能的影响

以草酸乙醇溶液为沉淀剂,采用不同的沉淀次序(并流、反加和正加)制备了CuO-ZnO-Al2O3/HZSM-5复合型催化剂,对CO2加氢直接合成二甲醚反应的催化活性顺序为:并流法催化剂>反加法催化剂>正加法催化剂。3种复合催化剂的还原温度由低到高的顺序为:并流法催化剂<反加法催化剂<正加法催化剂。在沉淀过程中,反加法和正加法均形成类胶体沉淀,相应催化剂的比表面积也较大。IR研究发现,催化剂在1101cm-1处表现Cu/Zn/Al氧化物与HZSM-5分子筛之间相互作用的IR吸收峰强度与其催化活性间存在对应关系。XRD结果表明,并流法得到的催化剂前驱体中有铜锌同形取代现象,有利于催化剂活性的发挥。

Study on Direct Synthesis of Dimethyl Ether from Carbon Dioxide Hydrogenation--Effects of Precipitation Order on Structure and Properties of Catalyst

Three composite catalysts(CuO-ZnO-Al_2O_3/HZSM-5) for dimethyl ether synthesis were prepared using oxalic acid ethanol solution as the precipitator,by parallel-flow,reverse and normal precipitation methods respectively.It was demonstrated by the activity of the catalyst that the parallel-flow-precipitation method was the best,and the reverse-precipitation was also much better than the normal one.The reduction temperatures order of the catalysts from low to high was: parallel-flow,reverse,and normal precipitation catalyst.Colloid precipitate formed in both the reverse and normal precipitation processes,so that the specific surface areas of these two catalysts rose.The IR results of the catalysts showed that there was a corresponding relation between the activity of the catalyst and the adsorption peak intensity at 1101cm~(-1),which indicated an interaction existed between the metal oxides and HZSM-5.The XRD characterization of the catalyst precursors revealed that the isomorphous substitution between copper and zinc could take place in the parallel-flow precipitation process,which might yield better catalytic activity.