CH_4 dissociation on the perfect and defective MgO(001) supported Ni_4

摘要

A theoretical understanding of CH_4 dissociation on Ni-based catalysts is of great importance for the development of CH_4 reforming catalysts with high activity and carbon-deposition resistance. Based on comparisons of CH_4 dissociation on perfect and defective MgO supported Ni_4, as well as Ni(111), the effects of the strong interactions between Ni_4 and MgO on CH_4 dissociation are systematically investigated by density functional theory (DFT) calculations. Our results indicate that the interaction between Ni_4 and the defective MgO is stronger than for the perfect MgO. Consequently, the adsorptions of CH_x(x = 0-4) are weaker than those on the perfect Ni_4/MgO. Hirshfeld charge analysis shows that electrons are transferred from MgO to Ni_4, then to CH_x adspecies; the stronger interactions between Ni_4 and MgO lead to less electronic transfer from Ni_4 to adspecies, which result in weaker adsorption of CH_x. Potential energy surface calculations of CH_4 dissociation indicate that there are lower energy barriers for the sequent dissociations of CH_4 → CH_2 + 2H and an appropriate barrier of CH oxidation matching up with that of CH_2 further dissociation on the model catalyst of Ni_4 supported on defective MgO. This might be an elementary requirement for an excellent CH_4 reforming catalyst, and may shed light on experimental catalyst development.