Monolayer Dispersed Ru-Zn Catalyst and Its Performance in the Selective Hydrogenation of Benzene to Cyclohexene

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. ：采用共沉淀法制备了一系列不同 Zn 负载量的 Ru-Zn 催化剂. XRD 和 XPS 结果表明, 催化剂中的 Zn 大部分以 ZnO 形式存在, 在加氢过程中催化剂表面的 ZnO 可以与浆液中的 Zn2+形成碱式硫酸锌盐. 随催化剂中 Zn 负载量的增加, 碱式硫酸锌盐的量也增加, 这导致催化剂活性降低和环己烯选择性升高. 当 Zn 负载量为 8.6% 时, 加氢后碱式硫酸锌盐在 Ru-Zn 催化剂表面上接近单层分散态. 单层分散型 Ru-Zn 催化剂催化性能最佳, 该催化剂在 140 °C, 5 MPa H2 下和 0.6 mol/L 硫酸锌溶液中预处理 22 h 后, 反应 20 min, 苯转化率 84.4% 时, 环己烯选择性为 69.8%.