Diffusion of benzene through water film confined in silica mesopores: Effect of competitive adsorption of solvent

Effect of ZnSO4, MnSO4 and FeSO4 on the Partial Hydrogenation of Benzene over Nano Ru-Based Catalysts

Nano Ru-based catalysts, including monometallic Ru and Ru-Zn nanoparticles, were synthesized via a precipitation method. The prepared catalysts were evaluated on partial hydrogenation of benzene towards cyclohexene generation, during which the effect of reaction modifiers, i.e., ZnSO₄, MnSO₄, and FeSO₄, was investigated. The fresh and the spent catalysts were thoroughly characterized by XRD, TEM, SEM, XPS, XRF, and DFT studies. It was found that Zn²⁺ or Fe²⁺ could be adsorbed on the surface of a monometallic Ru catalyst, where a stabilized complex could be formed between the cations and the cyclohexene. This led to an enhancement of catalytic selectivity towards cyclohexene. Furthermore, electron transfer was observed from Zn²⁺ or Fe²⁺ to Ru, hindering the catalytic activity towards benzene hydrogenation. In comparison, very few Mn²⁺ cations were adsorbed on the Ru surface, for which no cyclohexene could be detected. On the other hand, for Ru-Zn catalyst, Zn existed as rodlike ZnO. The added ZnSO4 and FeSO₄ could react with ZnO to generate (Zn(OH)₂)₅(ZnSO₄)(H₂O) and basic Fe sulfate, respectively. This further benefited the adsorption of Zn²⁺ or Fe²⁺, leading to the decrease of catalytic activity towards benzene conversion and the increase of selectivity towards cyclohexene synthesis. When 0.57 mol·L⁻¹ of ZnSO₄ was applied, the highest cyclohexene yield of 62.6% was achieved. When MnSO₄ was used as a reaction modifier, H₂SO₄ could be generated in the slurry via its hydrolysis, which reacted with ZnO to form ZnSO₄. The selectivity towards cyclohexene formation was then improved by the adsorbed Zn²⁺.