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

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 H-2 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.