A theoretical understanding of CH4 dissociation on Ni-based catalysts is of great importance for the development of CH4 reforming catalysts with high activity and carbon-deposition resistance. Based on comparisons of CH4 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 CH4 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 CHx(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 CHx 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 CHx. Potential energy surface calculations of CH4 dissociation indicate that there are lower energy barriers for the sequent dissociations of CH4 -> CH2 + 2H and an appropriate barrier of CH oxidation matching up with that of CH2 further dissociation on the model catalyst of Ni-4 supported on defective MgO. This might be an elementary requirement for an excellent CH4 reforming catalyst, and may shed light on experimental catalyst development. (C) 2014 Elsevier Ltd. All rights reserved.