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 MoS2(101¯0) Mo-edge, the dissociation of hydrogen with the formation of SH groups is an exothermic process and energetically most favoured. On a partially nickel-promoted (101¯0) surface, the dissociation of molecular hydrogen to form a surface SH group and a MoH or NiH species is an endothermic process, and requires higher energy than on an unpromoted (101¯0) Mo-edge surface. On a fully promoted (101¯0) Ni-edge, associative adsorption of H2 is exothermic, and dissociation to a pair of NiH and SH groups or two NiH species is endothermic. Hydrogen sulfide can be strongly adsorbed on the vacant nickel sites on the partially and fully nickel-promoted (101¯0) Mo-edge surface, and surface SH groups can be formed by dissociation of adsorbed H2S.