Selective hydrogenation of benzene to cyclohexene over monometallic ruthenium catalysts in the presence of CeO2 and ZnSO4 as co-modifiers

The monometallic Ru catalysts with the CeO2 without calcination and ZnSO4 as co-modifiers gave a cyclohexene yield of 58.5% at the optimum nominal CeO2/Ru molar ratio of 0.15. Moreover, this catalyst had a good stability. The chemisorbed (Zn(OH)2)3(ZnSO4)(H2O)3 salt on Ru surface, which was formed by the CeO2 reacting with ZnSO4, created the new Ru active sites suitable for the formation of cyclohexene and improved the selectivity to cyclohexene. In addition, the Zn2+ in the aqueous phase could form a stable complex with cyclohexene, stabilizing the cyclohexene in the liquid phase and improving the selectivity to cyclohexene. The calcination treatment of CeO2 was not beneficial for the enhancement of the selectivity to cyclohexene since it is difficult for the CeO2 calcinated to react with ZnSO4 to form the (Zn(OH)2)3(ZnSO4)(H2O)3 salt.