活性形貌对CuO/ZnO/Al_2O_3催化加氢反应的影响

Effect of Active Morphology on Catalytic Hydrogenation of CuO/ZnO/Al_2O_3

以硝酸铜、硝酸锌等为原料,采用沉淀-沉积法制备了载体是介孔Al_2O_3的CuO/ZnO/Al_2O_3催化剂,通过改变焙烧时间可得到不同活性组分形貌(团簇球状和棒状)的催化剂,并用于CO/CO_2加氢反应。通过XRD、BET、N_2吸附-脱附、TEM、H_2-TPR、CO_2-TPD、NH_3-TPD和FTIR对催化剂进行了表征与测试。结果表明,活性组分(CuO/ZnO)形貌的改变影响了催化剂的Cu O晶粒尺寸、比表面积、孔径及其还原性能,且对催化剂的酸性位点和碱性位点的相对数量影响较大。团簇球状催化剂中活性组分的分散度高、易还原、碱性位多、酸性位少,有利于甲醇的生成;而棒状催化剂中孔道不均匀、碱性位少、酸性位多,更有利于二甲醚(DME)的生成。活性测试结果表明,团簇球状催化剂表现出高甲醇选择性(95.05%)和低DME选择性(4.18%);棒状催化剂的产物选择性与团簇球状相反,表现出高DME选择性(75.41%)和低甲醇选择性(12.81%)。

CuO/ZnO/Al2O3 catalysts with mesoporous Al2O3 as support were prepared by precipitationdeposition method using cupric nitrate and zinc nitrate as raw materials.Catalysts possessing differen active component morphologies(globular clusters and rod-like structure)were obtained by changing calcination time and used for CO/CO2 hydrogenation reaction.The catalysts were characterized and tested by XRD,BET,N2 adsorption-desorption,TEM,H2-TPR,CO2-TPD,NH3-TPD and FTIR.The results showed that the morphology of the active components affects the CuO grain size,specific surface area,pore size and reduction performance of the catalyst and has a great influence on the relative quantity of acid sites and basic sites of the catalysts.The catalyst with globular clusters has high dispersion of active components easy to reduce,more basic sites and less acid sites,which is favorable for the formation of methanol.While the rod-like catalyst has uneven pores,less basic sites and more acid sites,which is more conducive to the formation of dimethyl ether(DME).The activity test results revealed that the catalyst with globular clusters exhibited high methanol selectivity(95.05%)and low DME selectivity(4.18%).The rod-like catalyst displayed the opposite trend with high DME selectivity(75.41%)and low methanol selectivity(12.81%).