还原介质和还原温度对Ru-Zn催化苯选择加氢制环己烯性能的影响

Effect of reduction medium and reduction temperature on the performance of Ru-Zn catalysts for selective hydrogenation of benzene to cyclohexene

用共沉淀法分别在5%NaOH溶液、蒸馏水、0.035mol/L ZnSO_4溶液和0.145mol/L ZnSO_4溶液中用H_2还原制备了Ru-Zn(5%NaOH)催化剂、Ru-Zn(H_2O)催化剂、Ru-Zn(0.035mol/L ZnSO_4)催化剂和Ru-Zn(0.145mol/L ZnSO_4)催化剂。结果表明,它们催化苯选择加氢制环己烯的活性高低顺序为Ru-Zn(5%NaOH)催化剂>Ru-Zn(H_2O)催化剂>Ru-Zn(0.035mol/L ZnSO_4)催化剂≈Ru-Zn(0.145mol/L ZnSO_4)催化剂,环己烯选择性高低顺序与活性顺序正好相反。因为还原介质可以影响Ru-Zn催化剂的组成和织构性质,进而影响它的催化性能。Ru-Zn(H_2O)催化剂的环己烯收率最高,说明蒸馏水作还原介质最好。随还原温度升高,Ru-Zn(H_2O)催化剂比表面积逐渐减小,催化剂活性逐渐降低。同时粒径逐渐增大,Ru粒子上有利于环己烯加氢生成环己烷的楞位和顶点位减少,环己烯选择性升高。在100℃还原温度下制备的Ru-Zn(H_2O)催化剂的环己烯收率可达58.1%。

The catalysts of Ru-Zn(5%NaOH),Ru-Zn(H2O),Ru-Zn(0.035mol/L ZnSO4)and Ru-Zn(0.145mol/L ZnSO4)were prepared by H2reduction in5%NaOH,distilled water,0.035mol/L ZnSO4and0.145mol/L ZnSO4using a co-precipitation method.The activities of the catalysts for selective hydrogenation of benzene to cyclohexene were in the order of:Ru-Zn(5%NaOH)>Ru-Zn(H2O)>Ru-Zn(0.035mol/L ZnSO4)≈Ru-Zn(0.145mol/L ZnSO4),but their selectivities to cyclohexene were in the inverse order.The reason is that the reduction media could influence the composition and texture properties of the Ru-Zn catalysts,and further affects their catalytic performance.The Ru-Zn(H2O)catalyst gave the highest cyclohexene yield among these catalysts,suggesting that the distilled water was the best reduction medium.The specific surface of Ru-Zn(H2O)catalysts decreased with the increase of the reduction temperature,and the activity of the catalysts was lowered.Meanwhile,the particle sizes of the Ru-Zn catalysts increased resulting in the decrease of numbers of the corner sites and the edge sites on the catalysts suitable for hydrogenation of cyclohexene to cyclohexane.Thus the selectivity to cyclohexene increased with the increase of the reduction temperature.The Ru-Zn(H2O)catalyst reduced at100℃gave a cyclohexene yield of58.1%.