Ru-Zn catalysts for selective hydrogenation of benzene using coprecipitation in low alkalinity

Abstract Several unsupported Ru-Zn catalysts were successfully prepared using the coprecipitation method under low alkaline conditions, and their catalytic performance was evaluated for the selective liquid-phase hydrogenation of benzene. The effect of the amount of ZnCl 2 added to the coprecipitation solution on the physical and catalytic properties of the Ru-Zn catalysts was studied whilst keeping the amount of the NaOH precipitant constant. The properties of the resulting catalysts were characterized by N 2 adsorption, X-ray diffraction, and temperature-programmed reduction. The effects of the stirring rate and the amount of ZnSO 4 additive on the catalytic properties of the Ru-Zn catalysts were investigated using the optimal Zn content. The recyclability of the optimal Ru-Zn catalyst was also explored. The results revealed that the optimal Zn content for the Ru-Zn catalysts was 16.7 wt%, and the selectivity for cyclohexene could reach up to 80% (yield > 45%) when the benzene conversion was 57% in an aqueous solution of ZnSO 4 (0.45 mol/L) under the optimal reaction conditions (i.e., hastelloy reactor, 1200 r/min, 150 °C and 5 MPa of H 2 pressure). The presence of ZnO crystals in the Ru catalysts was found to be critical to obtaining high selectivity for cyclohexene (>80%). The Ru-Zn catalysts prepared under the low alkaline conditions also showed good stability, which indicates that they could potentially be used for industrial application.