Density functional theory study of hydrogen sulfide dissociation on bi-metallic Ni-Mo catalysts

This work presents results on the dissociation of H₂S over Ni-Mo catalysts suggesting that the presence of surface Mo-atom(s) has a significant impact on both the energetics of the process and the reaction mechanism. The presence of one Mo atom provides an additional energetic advantage of 10.2 kcal/mol overall. While increasing the energetic advantage of the process, the presence of Mo atom also increases the activation barriers by at most 3 kcal/mol. The large exothermic nature of this process combined with the comparatively small activation barriers suggests that the H₂S dissociation process is a facile process on all of the surfaces studied here. Additionally, analysis was provided to explain the difference in catalytic behavior between a bi-metallic alloy and a bi-metallic sulfide. It was determined that the bi-metallic alloy binds sulfur strongly (>100 kcal/mol) which can be compared with the results of Sun and co-workers [M. Sun, A.E. Nelson, J. Adjaye, Catal. Today 105 (2005) 36] who predict that S adsorption on the metal sulfide phase is not energetically favorable. It is suggested that the sulfide surface does not bind S in an energetically favorable manner because the sulfide surface structure does not possess a binding site that can emulate the hollow site on a metal surface.