Synergistic effect of Cu and Ce bimetallic over MCM-41 zeolite for enhancing the catalytic hydrolysis performance of COS

Abstract

The presence of sulfur-containing impurities in natural gas not only diminishes its utilization value, but also results in the emission of sulfur-containing pollutants. In this study, a Cu-Ce bimetallic-loaded MCM-41 catalyst was prepared by ammonia evaporation method for the catalytic hydrolysis of carbonyl sulfide (COS). The desulfurization efficiency of Cu₂₅Ce₅/MCM-41 can reach a 100 % COS removal rate and maintain for 3.5 h. CuO furnishes the predominant weakly acidic and weakly basic sites for the desulfurization process, which are conducive to the adsorption of COS. Meanwhile, CeOx provides a greater abundance of moderately basic sites for the desulfurization process, which help to improve the removal efficiency of COS. The incorporation of Ce into the catalyst enhances the resistance to sulfur poisoning of Cu and prolongs the lifespan of the catalyst. The incorporation of Ce is capable of transforming the strongly basic sites on the surface of Cu₂₅/MCM-41 into moderately basic sites, avoiding excessive oxidation of H₂S. Additionally, the introduction of Ce offers a degree of protection for CuO, which improves the ability of the catalyst to resist sulfur poisoning. The combined effect of Cu and Ce was found to be instrumental in enhancing the adsorption of COS and in slowing down the oxidation of H₂S. The reduction of Cu²⁺ and Ce³⁺ indicated their direct participation in the oxidation of H₂S. Firstly, COS adsorbed on the catalyst surface is converted into H₂S and CO₂ through a catalytic hydrolysis reaction. Subsequently, H₂S adsorbed on the catalyst surface undergoes partial oxidation to sulfide, and partial further oxidation by oxygen-containing functional groups on the surface to S, SO₃^2-, and SO₄^2-, which results in the toxic deactivation of the catalyst.