助剂前体ZnSO4浓度对苯选择加氢制环己烯Ru-Zn催化剂性能的影响

Effect of the Concentration of the Promoter Precursor ZnSO_4 on the Performance of the Ru-Zn Catalyst for Selective Hydrogenation of Benzene to Cyclohexene

共沉淀法制备了Ru-Zn催化剂,在ZrO_2作分散剂下考察了助剂前体ZnSO_4浓度对苯选择加氢制环己烯Ru-Zn催化剂性能的影响.并用X-射线衍射(XRD)、X-射线荧光光谱(XRF)、N_2-物理吸附、透射电镜(TEM)和X-射线光电子能谱(XPS)等手段对催化剂进行了表征.结果表明,当ZnSO_4前体浓度低于0.10 mol/L时,Ru-Zn催化剂中Zn以ZnO形式存在,在加氢过程中ZnO可以与反应修饰剂ZnSO_4反应生成(Zn( OH)_2)_3(ZnSO_4)(H_2O)_3盐.继续增加ZnSO_4前体浓度,催化剂中Zn以ZnO和NaZn_4(SO_4)(Cl)(OH)_6·6H_2O盐存在,在加氢过程中ZnO和NaZn_4(SO_4)(Cl)(OH)_6·6H_2O盐可以与反应修饰剂ZnSO_4反应生成(Zn( OH)_2)_3(ZnSO_4)(H_2O)_5.(Zn( OH)_2)_3(ZnSO_4)(H_2O)_x(x=3或5)盐的Zn^(2+)可以转移金属Ru的部分电子.因此,随ZnSO_4前体浓度的增加,(Zn( OH)_2)_3(ZnSO_4)(H_2O)_x的量逐渐增加,金属Ru失电子越多,催化剂活性越低,环己烯选择性越高.0.08 mol/L ZnSO_4前体制备Ru-Zn催化剂给出了59.1%的环己烯收率,而且该催化剂具有良好的重复使用性能和稳定性.

The Ru-Zn catalysts were prepared by a co-precipitation method. The effect of the concentration of the promoter precursor ZnSO_4 on the performance of Ru-Zn catalysts for selective hydrogenation of benzene to cyclohexene was investigated with ZrO_2 as a dispersant. And the catalysts were characterized by X-ray diffraction（ XRD）,X-fluorescence（ XRF）,N_2 physisorption,transimission electron microscopy（ TEM）,and X-ray photoelectron spectroscopy（ XPS）. It was found that when the concentration of the promoter precursor ZnSO_4 was lower than 0. 10 mol / L the Zn in the Ru-Zn catalyst were mostly in the form of ZnO,which could react with the reaction modifier ZnSO_4 to form a（ Zn（ OH）_2）_3（ZnSO_4）（H_2O）_3 salt during the hydrogenation. When the concentration of the promoter precursor ZnSO_4 was further increased,the Zn in the catalyst existed as ZnO and a NaZn_4（SO_4）（Cl）（OH）_6·6H_2O salt. This salt and ZnO could be converted into a（ Zn（ OH）_2）_3（ZnSO_4）（H_2O）_5 salt by reacting with the reaction modifier ZnSO_4 during the hydrogenation. The Zn^（2＋）of the（ Zn（ OH）_2）_3（ZnSO_4）（H_2O）_x（x = 3or 5） salt could transform some electrons from metallic Ru. Therefore,the higher the concentration of the promoter precursor ZnSO_4,the more the（Zn（OH）_2）_3（ZnSO_4）（H_2O）_x salt formed,and the more electrons metallic Ru lost. And the activity of the Ru-Zn catalysts decreased and the selectivity to cyclohexene increased. The Ru-Zn catalyst prepared with the promoter precursor ZnSO_4 of 0. 08 mol / L gave a high cyclohexene yield of 59. 1%. Moreover,this catalyst exhibited a excellent reusability and a perfect stability.