Exploring the Reaction Mechanism of HS Decomposition with MS (M = Mo, W) Clusters.

HS 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 (HS) to produce hydrogen. In this study, density functional theory (DFT) calculations are carried out to explore the reaction mechanisms of HS with MS (M = Mo, W) clusters. The reaction mechanism of HS with MoS is roughly the same as that of the reaction with WS, and the free-energy profile of the reaction with MoS is slightly higher than that of the reaction with WS. The overall driving forces (-Δ) are positive, and the overall reaction barriers (Δ ) are rather small, indicating that such H productions are product-favored. MS (M = Mo, W) clusters have clawlike structures, which have electrophilic metal sites to receive the approaching HS molecule. After several hydrogen-atom transfer (HAT) processes, the final MS·H (IM-4) complexes are formed, which could desorb H at a relatively low temperature. The singlet product MS clusters contain the singlet S moiety, similar to the adsorbed singlet S on the surface of sulfide catalysts. The theoretical results are compared with the experiments of heterogeneous catalytic decomposition of HS by MoS catalysts. Our work may provide some insights into the optimal design of the relevant catalysts.