Partial hydrogenation of benzene on Ru-Zn/SiO₂ catalysts

A series of silica-supported ruthenium-zinc catalysts with various contents of zinc were prepared. These catalysts were characterized with temperature-programmed reduction (TPR), temperature-programmed desorption of hydrogen (H₂-TPD), and X-ray diffraction (XRD). The reaction of partial hydrogenation of benzene was carried out in a batch reactor at a pressure of 3.36 MPa. The reduction of Ru-Zn/SiO₂ catalysts occurs at a much higher temperature, as compared to the Ru/SiO₂ catalyst. The results suggested that ruthenium and zinc were in close proximity with each other. The reduction process of ruthenium oxide was retarded because of Ru-Zn interaction. The profiles of H₂-TPD for Ru-Zn/SiO₂ catalysts show two desorption peaks. The total amount of desorbed hydrogen decreased with an increase in the zinc concentration. The catalytic activity also decreased with an increase of the zinc concentration in the catalyst. The area of the low-temperature H₂-TPD peak, in contrast, increased with an increase of the zinc concentration. In addition, the selectivity to cyclohexene can be correlated with the area of this low-temperature desorption peak.