New insights into CO2 methanation mechanisms on Ni/MgO catalysts by DFT calculations: Elucidating Ni and MgO roles and support effects

Abstract

CO2 methanation mechanisms were investigated by DFT calculations on pure Ni(111), hydrogen-assisted MgO(110) and Ni/MgO surfaces to get insights into Ni and MgO roles and support effects on the mechanisms. For Ni/MgO catalysts, Ni is the active site and MgO acts as the promoter for CO2 methanation reaction. The role of Ni on the reaction is not only to decompose H2 to H atom but also the active site for CO2 hydrogenation. Compared with the pure Ni surface, Bader charge analysis has demonstrated strong metal–support interactions between Ni and MgO distinctly improve Ni reducibility of the Ni/MgO surface. This leads to that the C terminal of CO2 gains more electrons from the Ni/MgO surface, thus promoting the process of C-terminal hydrogenation on the surface. Consequently, CO2 methanation follows the formate pathway via the H2COO* intermediate on the Ni/MgO surface, differing from the formate pathway via the HCOOH* intermediate on the Ni(111) surface. In addition, the presence of MgO support is beneficial for the OH removal and then the H2O formation during CO2 methanation, due to the H-spillover effect and the strong OH adsorption on the MgO support.