Density functional theory calculation for H2 dissociation on MoS2 and NiMoS cluster models

Quantum chemical calculations for H2 dissociation on NiMoS and MoS2 catalysts were carried out using the ab initio density functional theory and the pseudopotential approaches. The catalysts were modeled by XMo4S17H16, X=Ni, Mo cluster models. Two dissociation route, the heterolytic and the homolytic, were studied on the MoS2 cluster model. The results show that the homolytic dissociation is favored over the heterolytic route. On the NiMoS cluster model, the homolytic route is less favored thermodynamically than in the MoS2. The topological analysis of the electron density indicates the presence of S2 groups on the MoS2 and NiMoS surfaces, as well as a Mo-Mo bond in the MoS2 model. No Ni-Mo bond was found in the NiMoS cluster model. The presence of Ni activates the Mo-S bond, produces a polarization at this bond and decreases the chemical hardness of the solid.