Solvent effect on the activity of Ru-Co₃O₄ catalyst for liquid-phase hydrogenation of CO₂ into methane

Ru-Co₃O₄ catalyst was prepared by the co-precipitation method. Its catalytic performance in liquid-phase hydrogenation of CO₂ into methane was investigated, and compared with those of the conventional Ru-based catalysts (Ru/SiO₂, Ru/CeO₂, Ru/ZrO₂, Ru/TiO₂) prepared by impregnation method. The solvents including H₂O, n-butanol, 1,4-butyrolactone, DMF, n-nonane, decalin, cyclohexane and isooctane had significant solvent effects on the catalytic performance. Compared with other solvents, the catalyst showed higher activity and selectivity catalytic performance when decalin and isooctane was applied as the solvent. At 200 °C and H₂/CO₂=3:1 (v/v, 4 MPa) and with decalin as the solvent, the conversion of CO₂ and the selectivity of CH₄ reached 45.6% and 97%, respectively. The isotope labeling experiments and in-situ diffuse reflectance infrared spectra showed that the hydrogen atoms of the tertiary carbon in decalin and isooctane were active for CO₂ hydrogenation reaction, thus improving the catalytic activity.