State-of-art modifications of heterogeneous catalysts for CO2 methanation - Active sites, surface basicity and oxygen defects

CO2 methanation has drawn tremendous attentions since it can alleviate the environmental issues caused by the rapid increase of CO2 and realize the carbon cycle. To effectively activate the stable CO2 molecule and facilitate the complicated 8 electron-involved process, it is necessary to develop highly efficient and robust catalysts, aiming at large-scale applications in CO2 methanation. In this review, three major modification strategies for improving the catalysts are discussed, including active sites, surface basicity and oxygen defects. A smaller size and higher dispersion of metallic sites enhance the adsorption of H2 and CO2, thus leading to a higher yield of CH4. Also, basic sites with medium strength promote the crucial intermediate formation while acidic sites or strong basic sites might adversely affect the CH4 production. Furthermore, oxygen defects increase the CO2 adsorption and oxygen mobility, gasifying the cokes and prolonging the lifespan. In addition to the structure -performance relationship, reaction and deactivation mechanisms are introduced at the beginning while conclusive remarks and future works are proposed in the end.