Dual Regulation of Oxygen Vacancies and Metal−Support Interaction in Ni/Ni x CeO2-γ for Synergistic Enhancement of Low-Temperature CO2 Methanation

Abstract

Catalytic CO2 methanation converts CO2 with hydrogen into methane, enabling carbon recycling and chemical energy storage. However, the precise roles and synergy of critical active sites, oxygen vacancies and metal–support interfaces remain elusive in CO2 methanation, impeding the development of highly active and selective low-temperature catalysts. Based on density functional theory calculations, herein, Ni-doped CeO2 supports were designed to load Ni nanoparticles for constructing Ni/NixCeO2-γ catalysts. With 2 mol % Ni doping, the Ni/Ni0.02CeO2-γ catalyst exhibited 75.5% CO2 conversion and 100% CH4 selectivity at 250 °C, and maintained its activity over 200 h at 300 °C. Compared to Ni/CeO2, Ni/Ni0.02CeO2-γ features smaller CeO2 nanoparticles, higher oxygen vacancy concentration, and stronger metal–support interaction. The abundant oxygen vacancies create frustrated Lewis pairs with adjacent basic sites (e.g., hydroxyls and lattice oxygen) for effective CO2 adsorption and activation, while the strong metal–support interaction facilitated the adsorption and dissociation of H2 on the metallic Ni sites. Consequently, the above synergy boosted key steps including hydrogen spillover and intermediate hydrogenation, resulting in a marked improvement in the CO2 methanation rate at low temperatures. The in situ diffuse-reflectance infrared Fourier transform spectroscopy revealed that the formate pathway served as the principal reaction mechanism for CO2 methanation over Ni/Ni0.02CeO2-γ. This study elucidates the role of oxygen vacancy-mediated synergy in low-temperature CO2 methanation and offers a strategy for designing CO2 hydrogenation catalysts.