Mechanistic understanding of CO2 hydrogenation to methane over Ni/CeO2 catalyst

Abstract

Ni/CeO2 is considered as a potentially efficient catalyst for CO2 methanation. Herein, all possible reaction pathways of CO2 methanation were investigated by the first-principles calculations based on density functional theory to uncover the intrinsic reaction mechanism over Ni/CeO2 catalyst. Theoretical analysis results indicate that the strong metal-support interaction between Ni nanoparticle and CeO2 support is closely associated with the transfer and accumulation of electrons towards the interface. Ni nanocluster on Ni/CeO2 catalyst is the most active adsorption and activation site of CO2 molecule. CO2 methanation over Ni/CeO2 catalyst is mainly governed by the RWGS + CO-hydro pathway, rather than the pathways of formate formation and direct CO bond cleavage. The main reaction channel of CO2 methanation is CO2* → HOCO* → CO* → HCO* → H2CO* → CH2* → CH3* → CH4*. H-assisted CO bond breakage of H2CO* plays a critical role in CO2 methanation, and is the rate-limiting step of RWGS + CO-hydro pathway. The optimal pathway and rate-limiting step of CO2 methanation are altered in the presence of CeO2. A complete reaction network is proposed for further understanding the molecular-level reduction mechanism of CO2 hydrogenation to methane on Ni/CeO2 catalyst.