Abstract: A series of Ru-Zn catalysts with different Zn loadings were prepared by co-precipitation. X-ray diffraction and X-ray photoelectron spectroscopy results showed that a large part of the Zn in the Ru-Zn catalysts were present in the form of ZnO and the ZnO on the catalyst surface could react with ZnSO₄ in the slurry to form a basic zinc sulfate salt during hydrogenation. The content of the basic salt increased with an increase in the Zn loading of the catalysts. This resulted in a decrease in catalyst activity and an increase in selectivity for cyclohexene. When the Zn loading was 8.6%, the basic salt dispersion was close to monolayer dispersion on the catalyst surface. When the catalysts were pretreated in the presence of 0.6 mol/L ZnSO₄ solution at 140 °C and at 5 MPa H₂, a cyclohexene selectivity of 69.8% and a benzene conversion of 84.4% was achieved after 20 min.

Key words: monolayer dispersion, ruthenium, zinc, benzene, selective hydrogenation, cyclohexene