Insight into the reaction route of CO2 methanation: Promotion effect of medium basic sites

•CO2 methanation mechanism is compared on Ni/Ce0.5Zr0.5O2 and Ni/γ-Al2O3.•The only difference of the mechanism is the reactive basic sites.•Medium basic sites are proposed to promote the formation of monodentate formate.•Monodentate formate could be hydrogenated quickly compared with bidentate formate.•Medium basic sites are proposed to enhance the activity of CO2 methanation.

Ce0.5Zr0.5O2 and γ-Al2O3 supported nickel catalysts were investigated for CO2 adsorption and methanation using in-situ FTIR spectroscopy. The reaction pathway on Ni/γ-Al2O3 is similar to that on Ni/Ce0.5Zr0.5O2, only differing in reactive basic sites. CO2 adsorption on medium basic sites of Ni/Ce0.5Zr0.5O2 results in monodentate carbonates. CO2 adsorbed on strong basic sites of Ni/γ-Al2O3 will not participate in the reaction. It was assumed that monodentate formate derived from monodentate carbonate on medium basic sites, could be hydrogenated more quickly than bidentate formate derived from hydrogen carbonate. Medium basic sites were proposed to enhance CO2 methanation activity.

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