Adsorption and dissociation of H2S on monometallic and monolayer bimetallic Ni/Pd(111) surfaces: A first-principles study

Periodic density functional theory calculations have been performed to investigate the adsorption structures and dissociative reaction pathways for H2S molecule on Ni(111), Pd(111) and Ni/Pd(111) monolayer bimetallic surfaces with surface monolayer and subsurface monolayer structures. Our results indicate that, for the molecular adsorption mode, the introducing Pd atoms on Ni(111) can enhance the binding strength between H2S and the surface, while an opposite effect is achieved when the Ni monolayer is formed on Pd(111) surface. The decompositions of H2S molecule on all Ni/Pd(111) surfaces are exothermic, especially for the surfaces that the top layer is composed of Ni atoms. According to the predicted minimum energy paths that connect the molecular and dissociative states, two elementary steps are found for all Ni/Pd(111) metal surfaces, and the breaking of the first HS bond is the rate-determining step for the H2S dissociation. Our results reveal that in most cases, the decomposition of H2S molecule on the monometallic and Ni/Pd(111) monolayer bimetallic surfaces is easy to happen. However, on the monolayer Ni-Pd(111) surface, there is a competition between the trapping-desorption channel and activated dissociation channel, which implies that depositing one monolayer Ni on a Pd(111) surface may help reducing sulfur poisoning by hindering the dissociation of H2S molecule.