Highly Selective and Stable Hydrogenation of CO ₂ /H ₂ S to Methyl Mercaptan over a Synergistic Cu−Mo Catalyst

Selective hydrogenation of carbon dioxide (CO2) with hydrogen sulfide (H2S) to methyl mercaptan (CH3SH) offers a strategy for the simultaneous utilization of CO2 and H2S waste gases from chemical processes. However, achieving activation of the C=O bond while maintaining high CH3SH selectivity remains a challenge. In this study, we report a Cu-doped porous spherical KMoS2/SiO2 catalyst (4CuKMo/SiO2) that overcomes this challenge to afford selective CH3SH synthesis. Under optimized conditions (1.5 MPa, 320 °C), the catalyst achieves a CO2 conversion of 28% with 96% CH3SH selectivity. Furthermore, the catalytic activity remains stable with no sharp degradation over a continuous 160-h operation. Mechanistic studies reveal that the Cu doping promotes the formation of sulfur vacancies, which facilitate the adsorption and activation of both CO2 and H2S. In addition, the synergistic interaction between Cu and Mo species redirects the reaction pathway from the typical COS intermediate route to a thermodynamically favorable CH3OH-mediated pathway, thereby enhancing the selective formation of CH3SH.