A series of Ru-based catalysts for CO2 methanation at low temperature were synthesized by the dispersion of Ru nanoparticles in different 1-butyl-3-methylimidazolium ionic liquids on a silica support. The effect of various ionic liquids and loadings on the physicochemical properties of the catalysts and the methanation catalytic activity were investigated. The Ru/[BMIM]BF4(1:10)/SiO2 catalyst demonstrated the best catalytic performance with CO2 conversion of 70.47% at 250 degrees C, which was related to the highly dispersed small Ru nanoparticles, basic property, and readily reducible RuO2 species. The results revealed that ionic liquids can not only be used as a protectant to effectively prevent the aggregation and oxidation of the nanoparticles by space resistance and electrostatic protection, but can also be adsorbed on the surface of Ru nanoparticles as a modification layer with strong adsorption to ultimately determine the size of the nanoparticles and maintain high dispersion, which can significantly affect the catalytic activity.