Catalytic Hydrogenation of Carbon Dioxide to Methanol by a Homogenous Ruthenium(II) Hydrido Carbonyl Complexes

Abstract

Ruthenium(II) hydrido carbonyl complexes [RuH(CO)(CH3CN)2(PPh3)2]+X- [X=BF4 (1), PF6 (2)] were synthesized and characterized spectroscopically. The molecular structure of 2 was determined by single crystal X-ray diffraction technique. Structure study for 2 revealed a mononuclear complex about the ruthenium centre which is distorted octahedral. These complexes were used as catalysts towards catalytic hydrogenation of CO2 to methanol at 90°C in an integrated one-pot system where CO2 was hydrogenated to methanol with high yields in acid media. Among the two ruthenium-based catalysts, 1 showed superior catalytic performance compared to 2 when the amount of catalyst was reduced. This difference is attributed to the varying proton-accepting abilities of the counterions, which affected the catalytic rate. The catalytic performance makes [RuH(CO)(PPh3)2(CH3CN)2]BF4, a potential candidate for realizing the large-scale production of methanol by CO2 hydrogenation. Here, we conclude that aluminum tris(trifluoromethanesulfonate) acid has shown superior catalytic activity over other acidic media for the conversion of CO2 to methanol in a scalable process.