Selective hydrogenation of benzene to cyclohexene over Ce-promoted Ru catalysts

Ru-Ce catalysts were prepared by a co-precipitation method. The effects of Ce precursors with different valences and Ce contents on the catalytic performance of Ru-Ce catalysts were investigated in the presence of ZnSO4. The Ce species in the catalysts prepared with different valences of the Ce precursors all exist as CeO2 on the Ru surface. The promoter CeO2 alone could not improve the selectivity to cyclohexene of Ru catalysts. However, almost all the CeO2 in the catalysts could react with the reaction modifier ZnSO4 to form (Zn(OH)2)3(ZnSO4)(H2O)3 salt. The amount of the chemisorbed salt increased with the CeO2 loading, resulting in the decrease of the activity and the increase of the selectivity to cyclohexene of Ru catalyst. The Ru-Ce catalyst with the optimum Ce/Ru molar ratio of 0.19 gave a maximum cyclohexene yield of 57.4%. Moreover, this catalyst had good stability and excellent reusability.