Al2O3含量对Cu-ZnO-Al2O3-SiO2催化剂性能的影响

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.

Effect of Al2O3 Content on the Catalytic Performance of Cu-ZnO-Al2O3-SiO2 Catalysts

The effects of Al_2O_3 content on the catalytic performance of Cu-ZnO-Al_2O_3-SiO_2 catalysts used for the synthesis of dimethyl ether(DME) from CO_2 by addition of H_2 were investigated.And these catalysts were characterized by XRD,H_2-TPR,XPS,NH_3-TPD and CO_2-TPD techniques.The results show that Al_2O_3 delays the growth of CuO and ZnO and makes the reduction of catalysts difficult.The added Al_2O_3 is accumulated on the catalysts' surface,which changes mole fraction of Cu~(2+) and Zn~(2+) in the surface of the catalytic.Besides,Al_2O_3 incorporates into the SiO_2 to form non-definite-shape mixture phase of Al_2O_3 and SiO_2,which provide the acid-base sites for ether formation.The reaction results shows that the addition of Al_2O_3 exhibits a promoting effect on the CO_2 conversion only when its mass fraction is below 1.4%.And an optimal DME yield is obtained when the mass fraction of Al_2O_3 is 4.0%,indicating a better 'synergistic effect'presented between the methanol forming and the methanol dehydration active sites in Cu-ZnO-Al_2O_3-SiO_2 catalysts.The research shows that Al_2O_3 affects the interaction between CuO and Al_2O_3 and the surface acidity of catalyst and further makes the Cu-ZnO-Al_2O_3-SiO_2 catalyst exhibit different catalytic performance on the synthesis of dimethyl ether(DME) from CO_2 by addition of H_2.