Exploring the Reaction Mechanism of H₂S Decomposition with MS₃ (M = Mo, W) Clusters

H₂S is abundantly available in nature, and it is a common byproduct in industries. Molybdenum sulfides have been proved to be active in the catalytic decomposition of hydrogen sulfide (H₂S) to produce hydrogen. In this study, density functional theory (DFT) calculations are carried out to explore the reaction mechanisms of H₂S with MS₃ (M = Mo, W) clusters. The reaction mechanism of H₂S with MoS₃ is roughly the same as that of the reaction with WS₃, and the free-energy profile of the reaction with MoS₃ is slightly higher than that of the reaction with WS₃. The overall driving forces (-ΔG) are positive, and the overall reaction barriers (ΔG _b) are rather small, indicating that such H₂ productions are product-favored. MS₃ (M = Mo, W) clusters have clawlike structures, which have electrophilic metal sites to receive the approaching H₂S molecule. After several hydrogen-atom transfer (HAT) processes, the final MS₄·H₂ (IM-4) complexes are formed, which could desorb H₂ at a relatively low temperature. The singlet product MS₄ clusters contain the singlet S₂ moiety, similar to the adsorbed singlet S₂ on the surface of sulfide catalysts. The theoretical results are compared with the experiments of heterogeneous catalytic decomposition of H₂S by MoS₂ catalysts. Our work may provide some insights into the optimal design of the relevant catalysts.