Solvent-Free Ball-Milling-Derived Ni-CeO2/SiO2 Catalysts for CO2 Methanation

The production of synthetic natural gas from captured CO2 and green H2 via methanation presents a compelling solution to long-term energy storage challenges and the imperative to mitigate CO2 emissions. In this study, we developed a facile solvent-free ball-milling technique to prepare CeO2-doped, SiO2-supported Ni-based catalysts for CO2 methanation. The effects of Ni loading (10–40 wt %), CeO2 content (0–10 wt %), and citric acid/Ni molar ratio (0–1) on the properties and catalytic performance of the catalysts were extensively investigated. The results demonstrate the critical role of Ni particle size and oxygen vacancy concentration in determining catalytic performance. In general, smaller Ni particle size and higher oxygen vacancy concentration enhance the CO2 conversion, although excessively small Ni particles (≤3 nm) detrimentally impact CH4 selectivity by promoting the reverse water gas shift reaction. The optimal catalyst, synthesized with a citric acid/Ni molar ratio of 0.15, contains 30 wt % Ni and 1 wt % CeO2, exhibiting stable CO2 conversion (81%) and CH4 selectivity (99%) over an 80-h time on stream under reaction conditions of 350 °C, H2/CO2 molar ratio of 4, and a gas hourly space velocity of 60 000 mL/(g·h). The developed solvent-free ball-milling technique is environmentally benign, economically viable, and readily scalable, offering a promising avenue for large-scale catalyst production that is essential for the practical application of CO2 methanation.