Al_2O_3含量对Cu-ZnO-Al_2O_3-SiO_2催化剂性能的影响

Effect of Al_2O_3 Content on the Catalytic Performance of Cu-ZnO-Al_2O_3-SiO_2 Catalysts

研究了Al2O3含量对Cu-ZnO-Al2O3-SiO2催化剂在CO2加氢合成二甲醚中催化性能的影响,并用XRD,H2-TPR,XPS,NH3-TPD和CO2-TPD等手段进行了表征。研究结果表明,Al2O3延缓了CuO和ZnO晶粒的长大,同时使催化剂变得难以还原。加入的Al2O3富集于催化剂表面,改变了催化剂表面Cu2+和Zn2+的摩尔分数。Al2O3还与SiO2产生无定形SiO2-Al2O3混合相,提供二甲醚合成所必需的酸碱中心。反应结果表明,Al2O3在催化剂中的质量分数低于1.4%时,对转化率的提高有促进作用;当Al2O3在催化剂中的质量分数为4.0%时,甲醇合成以及甲醇脱水的活性中心呈现出较好的“协同催化效应”,目标产物二甲醚的收率最高。研究认为,Al2O3通过影响CuO与Al2O3之间的相互作用以及催化剂的表面酸性,从而使催化剂对CO2加氢合成二甲醚表现出不同的催化性能。

The effects of Al2O3 content on the catalytic performance of Cu - ZnO - Al2O3 - SiO2 catalysts used for the synthesis of dimethyl ether （DME） from CO2 by addition of H2 were investigated. And these catalysts were characterized by XRD, H2 - TPR, XPS, NH3 - TPD and CO2 - TPD techniques. The results show that Al2O3 delays the growth of CuO and ZnO and makes the reduction of catalysts difficult, The added Al2O3 is accumulated on the catalysts＇ surface, which changes mole fraction of Cu^2＋ and Zn^2＋ in the surface of the catalytic. Besides, Al2O3 incorporates into the SiO2 to form non definite - shape mixture phase of Al2O3. and SiO2, which provide the acid - base sites for ether formation. The reaction results shows that the addition of Al2O3 exhibits a promoting effect on the CO2 conversion only when its mass fraction is below 1,4%. And an optimal DME yield is obtained when the mass fraction of Al2O3 is 4.0%, indicating a better ＇ synergistic effect＇ presented between the methanol forming and the methanol dehydration active sites in Cu - ZnO - Al2O3 - SiO2 catalysts. The research shows that Al2O3 affects the interaction between CuO and Al2O3 and the surface acidity of catalyst and further makes the Cu ZnO- Al2O3 - SiO2 catalyst exhibit different catalytic perfrmance on the synthesis of dimethyl ether （DME） from CO2 by addition of H2.