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

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.

Effect of the concentration of the promoter precursor ZnSO4 on the performance of the Ru-Zn catalyst for selective hydrogenation of benzene to cyclohexene

The Ru-Zn catalysts were prepared by a co-precipitation method. The effect of the concentration of the promoter precursor ZnSO4 on the performance of Ru-Zn catalysts for selective hydrogenation of benzene to cyclohexene was investigated with ZrO2 as a dispersant. And the catalysts were characterized by X-ray diffraction (XRD), X-fluorescence (XRF), N2 physisorption, transimission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that when the concentration of the promoter precursor ZnSO4 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 ZnSO4 to form a (Zn(OH)2)3(ZnSO4)(H2O)3 salt during the hydrogenation. When the concentration of the promoter precursor ZnSO4 was further increased, the Zn in the catalyst existed in ZnO and a NaZn4(SO4)(Cl)(OH)6•6H2O salt. This salt and ZnO could be converted into a (Zn(OH)2)3(ZnSO4)(H2O)5 salt by reacting with the reaction modifier ZnSO4 during the hydrogenation. The Zn2+ of the (Zn(OH)2)3(ZnSO4)(H2O) x (x=3 or 5) salt could transform some electrons from metallic Ru. Therefore, the higher the concentration of the promoter precursor ZnSO4, the more the (Zn(OH)2)3(ZnSO4)(H2O) 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 ZnSO4 of 0.08 mol/L gave a high cyclohexene yield of 59.1%. Moreover, this catalyst exhibited a excellent reusability and a perfect stability.