Samarium oxide (Sm₂O₃) is a versatile surface for CO₂ and H₂ interaction and conversion. Samarium oxide-supported Ni, samarium oxide-supported Co-Ni, and samarium oxide-supported Ru-Ni catalysts were tested for CO₂ methanation and were characterized by X-ray diffraction, nitrogen physisorption, infrared spectroscopy, H₂-temperature programmed reduction, and X-ray photoelectron spectroscopy. Limited H₂ dissociation and widely available surface carbonate and formate species over 20 wt.% Ni, dispersed over Sm₂O₃, resulted in ~98% CH₄ selectivity. The low selectivity for CO could be due to the reforming reaction between CH₄ (methanation product) and CO₂. Co-impregnation of cobalt with nickel over Sm₂O₃ had high surface adsorbed oxygen and higher CO selectivity. On the other hand, co-impregnation of ruthenium and nickel over Sm₂O₃ led to more than one catalytic active site, carbonate species, lack of formate species, and 94% CH₄ selectivity. It indicated the following route of CH₄ synthesis over Ru-Ni/Sm₂O₃; carbonate → unstable formate → CO → CH₄.