分子筛硅铝比及晶粒粒径对Cu-ZnO-Al_2O_3/HZSM-5催化剂直接合成二甲醚反应性能的影响

Effects of silicon to aluminum ratio and crystal size of zeolite on catalytic properties of Cu-ZnO-Al_2O_3/HZSM-5 for the direct synthesis of dimethyl ether from syngas

采用水热晶化法合成了硅铝比(SiO2/Al2O3)为60、120、200和晶粒粒径分别为1.00和0.25μm的HZSM-5分子筛,并以其为甲醇脱水活性组分与铜基甲醇合成活性组分(Cu-ZnO-Al2O3)组成双功能催化剂(Cu-ZnO-Al2O3/HZSM-5),在连续流动加压固定床反应器上考察了Cu-ZnO-Al2O3/HZSM-5对合成气直接制二甲醚反应的催化性能。结果表明,随着分子筛硅铝比的提高,二氧化碳副产物的生成量逐渐减少,从而使目的产物二甲醚的选择性逐渐增大。与常规分子筛相比,小晶粒分子筛的反应活性接近,但二氧化碳和烃类副产物的选择性较低。

A series of HZSM-5 zeolite samples with different n（SiO2）/n（Al2O3） ratios and crystal sizes were hydrothermally synthesized and physically mixed with a methanol synthesis component（CuO-ZnO-Al2O3） to form hybrid catalysts.The direct synthesis of dimethyl ether（DME） from syngas was carried out over the prepared hybrid catalysts in a pressurized fixed-bed under continuous flow conditions.The results indicated that the selectivity for CO2 decreased with the increase of n（SiO2）/n（Al2O3） ratios in HZSM-5 zeolite due to the decrease in the amount and strength of the acid sites,so the selectivity for DME was enhanced greatly.On the other hand,although the activity was not enhanced on the smaller sized HZSM-5 compared to the larger sized one,the selectivity for CO2 and hydrocarbons was decreased evidently.