A density functional theory study of methane activation on MgO supported Ni 9 M 1 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. CH 4 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 CH 4 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 CH 4 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 CH 4 at different Ni-M clusters, the Mulliken atomic charge was analyzed. In general, the electron gain of CH 4 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 CH 4 raises with the CH 4 electron gain increasing. This work provides insights into understanding the role of promoter metal M on thermal-catalytic activation of CH 4 over Ni/MgO catalysts, and is useful to interpret the reaction at an atomic scale.