Adsorption and dissociation of H2 and H2S on MoS2 and NiMoS catalysts

The formation and stable structures of surface hydrogen species on unpromoted and nickel-promoted MoS2 catalyst surfaces is studied by investigating the adsorption and dissociation of molecular hydrogen and hydrogen sulfide using periodic DFT calculations under generalized gradient approximation (GGA). On the stable image Mo-edge, the dissociation of hydrogen with the formation of single bondSH groups is an exothermic process and energetically most favoured. On a partially nickel-promoted image surface, the dissociation of molecular hydrogen to form a surface single bondSH group and a Mosingle bondH or Nisingle bondH species is an endothermic process, and requires higher energy than on an unpromoted image Mo-edge surface. On a fully promoted image Ni-edge, associative adsorption of H2 is exothermic, and dissociation to a pair of Nisingle bondH and single bondSH groups or two Nisingle bondH species is endothermic. Hydrogen sulfide can be strongly adsorbed on the vacant nickel sites on the partially and fully nickel-promoted image Mo-edge surface, and surface single bondSH groups can be formed by dissociation of adsorbed H2S.