A density functional theory study of methane activation on MgO supported Ni9M1 cluster: role of M on C-H activation

Methane activation is a pivotal step in the application of natural gas converting into high-value added chemicals via methane steam/dry reforming reactions. Ni element was found to be the most widely used catalyst. In present work, methane activation on MgO supported Ni-M (M = Fe, Co, Cu, Pd, Pt) cluster was explored through detailed density functional theory calculations, compared to pure Ni cluster. CH4 adsorption on Cu promoted Ni cluster requires overcoming an energy of 0.07 eV, indicating that it is slightly endothermic and unfavored to occur, while the adsorption energies of other promoters M (M = Fe, Co, Pd and Pt) are all higher than that of pure Ni cluster. The role of M on the first C-H bond cleavage of CH4 was investigated. Doping elements of the same period in Ni cluster, such as Fe, Co and Cu, for C-H bond activation follows the trend of the decrease of metal atom radius. As a result, Ni-Fe shows the best ability for C-H bond cleavage. In addition, doping the elements of the same family, like Pd and Pt, for CH4 activation is according to the increase of metal atom radius. Consequently, C-H bond activation demands a lower energy barrier on Ni-Pt cluster. To illustrate the adsorptive dissociation behaviors of CH4 at different Ni-M clusters, the Mulliken atomic charge was analyzed. In general, the electron gain of CH4 binding at different Ni-M clusters follows the sequence of Ni-Cu (−0.02 e) < Ni (−0.04 e) < Ni-Pd (−0.08 e) < Ni-Pt (−0.09 e) < Ni-Co (−0.10 e) < Ni-Fe (−0.12 e), and the binding strength between catalysts and CH4 raises with the CH4 electron gain increasing. This work provides insights into understanding the role of promoter metal M on thermal-catalytic activation of CH4 over Ni/MgO catalysts, and is useful to interpret the reaction at an atomic scale.