助剂Fe和反应修饰剂修饰的Ru催化剂上苯选择加氢制环己烯

共沉淀法制备了Ru-Fe(x)催化剂,并利用X射线衍射(XRD)、X射线荧光光谱(XRF)、N2物理吸附和透射电镜等手段对催化剂进行了表征.结果表明,Ru-Fe(x)催化剂中助剂Fe以Fe3O4形式存在.单独Fe3O4并不能提高Ru催化剂的环己烯选择性.但在加氢过程中Fe3O4可与反应修饰剂ZnSO4反应生成(Zn(OH)2)3(ZnSO4)(H2O)x(x=1 or 3).化学吸附的(Zn(OH)2)3(ZnSO4)(H2O)x(x=1 or 3)在提高Ru催化剂环己烯选择性中起着关键作用.此外,Ru-Fe(x)催化剂的性能还与浆液中的Zn2+浓度和pH值有关.在0.61 mol/L ZnSO4溶液中Ru-Fe(0.47)催化剂不但给出了56.7%的环己烯收率,而且具有良好的稳定性和重复使用性能.化学吸附在Ru表面的Fe2+同样能提高Ru催化剂的环己烯选择性.在0.29 mol/L和0.61 mol/L FeSO4溶液中Ru-Fe(0.47)催化剂上化学吸附Fe2+量近似,性能近似.因为Fe2+和Zn2+性质的差异,在0.29 mol/L和0.61 mol/L FeSO4溶液中Ru-Fe(0.47)催化剂的环己烯选择性分别低于在同浓度的ZnSO4溶液中的.

Selective hydrogenation of benzene to cyclohexene over the Ru catalyst modified by the promoter Fe and the reaction modifiers

The Ru-Fe(x) catalysts were prepared by a co-precipitation method. The catalysts were characterized by X-ray diffraction (XRD), X-fluorescence (XRF), N2 physisorption and transimission electron microscopy (TEM). The results showed that the promoter Fe existed as Fe3O4 in the catalysts. The Fe3O4 alone could not improve the selectivity to cyclohexene of Ru catalyst. However, the Fe3O4 on the surface could react with the reaction modifier ZnSO4 to form the (Zn(OH)2)3(ZnSO4)(H2O)x (x=1 or 3) salt. The chemisorbed (Zn(OH)2)3(ZnSO4)(H2O)x (x=1 or 3) salt played a key role in improving the selectivity to cyclohexene. Besides, the performance of the Ru-Fe(0.47) catalyst was closely related to the concentration of Zn2 and the pH values of the slurry. The Ru-Fe(0.47) catalyst gave a cyclohexene yield of 56.7% in the presence of 0.61 M ZnSO4. The reaction modifier FeSO4 also could enhance the selectivity to cyclohexene of the Ru-Fe(0.47) catalyst since the chemisorbed Fe2 could not be reduce to the metallic Fe on Ru surface. The Ru-Fe(0.47) catalyst exhibited the similar performance in 0.29 M and 0.61 M of FeSO4 solutions due to the similar amounts of the chemisorbed Fe2 . The Ru-Fe(0.47) catalyst showed the lower selectivity to cyclohexene in 0.29 M and 0.61 M of ZnSO4 solutions than that in the same concentrations of ZnSO4 for the different natures of Fe2 and Zn2 .