A density functional theory study of CO methanation mechanism on Ni4/SiC catalyst

Abstract

The reaction mechanism of CO methanation on the Ni4/3C-SiC(1 1 1) catalyst surface was explored by the density functional theory in this paper. The configuration of Ni4/3C-SiC(1 1 1) is built and the binding energy of Ni4 cluster on Ni4/3C-SiC(1 1 1) is higher than that on Ni4/t-ZrO2 and Ni4/Al2O3 surface, which may be contributed to improve the dispersion and stability of Ni-based catalyst. And the main pathway of CH4 formation on Ni4/3C-SiC(1 1 1) surface is CO + H → CHO + H → CH2O + H → CH3O → CH3 + H → CH4. The results show that the rate-determining step for CO methanation on Ni4/3C-SiC(1 1 1) is the formation of CH3 from CH3O dissociation with an energy barrier of 241.3 kJ/mol, which is lower than that on Ni4/t-ZrO2. In addition, the activation energy of CH3OH formation is higher than that of CH4 synthesis on Ni4/3C-SiC(1 1 1) surface (254.5 vs. 241.3 kJ/mol). Different from Ni(1 1 1), Ni4/γ-Al2O3, and Ni4/t-ZrO2 catalysts, the Ni4/3C-SiC(1 1 1) catalyst has a much higher selectivity for CH4 in the reaction of CO methanation, which may be attributed to the lower activation energy of CH3O dissociation to CH3 than that hydrogenation to CH3OH. Therefore, Ni4/3C-SiC(1 1 1) can be recommended preferentially for CH4 synthesis via CO hydrogenation, rather than CH3OH formation.