Novel Reaction-Adsorption Method for Preparation of Ru–Zn–La/ZrO2 Catalysts with High Catalytic Performance for Selective Hydrogenation of Benzene

Abstract

A novel wet-chemistry reaction-adsorption strategy via the facile acid–base interaction under mild conditions is demonstrated to fabricate the state-of-the-art Ru–Zn–La/ZrO2 catalysts for selective hydrogenation of benzene to cyclohexene. The catalyst preparation process is systematically investigated and verified with the combination of various characterization techniques. Preloading of lanthanide salts and alkali treatment after calcination not only favor the introduction of ruthenium and zinc species in the later stages but also help enhance the dispersion of the catalysts. The reaction rate constants (k1 and k2) decrease with the increment of the Zn/Ru molar ratio, and the selectivity at 40% conversion (S40) is positively correlated with the k1/k2 ratio, demonstrating the role of Zn species in retarding the hydrogenation activity of Ru and improvement of the selectivity to cyclohexene. In general, the catalytic behavior is dependent on the particle size of Ru, the La-to-Ru electron transfer effect, the content of Zn species, and the surface hydrophilicity of catalyst. These factors are generated by using different precursors and various predesigned La/Ru molar ratios in the preparation recipe. Moreover, a passivation treatment before the hydrogenation reaction can promote the cyclohexene selectivity of the catalyst Ru–Zn–La/ZrO2 (1.6 La/Ru) to 80.6% at a benzene conversion of 43.7%, which meets the industrial requirement. Notably, the specific activity of the catalyst is as high as 1224 gBZ·gRu–1·h–1, over 10 times higher than the industrial criterion. This work provides new insights into the design of Ru-based catalysts for benzene hydrogenation and other hydrogenation reactions as well.