The hydrogenation of CO2 to methanol as a useful bulk chemical and fuel has been receiving increased attention.[1] Herein, we describe catalytic hydrogenation of CO2 to methanol using multinuclear iridium complexes in a gas–solid phase reaction under mild reaction conditions.[2] In our previous study, we have reported that hydrogenation of CO2 in a neutral aqueous solution afforded mainly formic acid even under high pressure conditions.[3] We concluded that the equilibrium limitation between FA and CO2/H2 in water suppresses further hydrogenation of formic acid. We envisioned an alternate route to circumvent the equilibrium limitation. Dinuclear iridium complex under gas-solid phase conditions hydrogenated CO2 to give methanol with high selectivity under mild reaction conditions (Table). On the other hand, using mononuclear analog produced a very small amount of methanol on prolonging the reaction time. It has been attributed to hydride complex formation upon exposure to H2 gas, suppression of the liberation of FA under gas-solid phase reaction conditions, and intramolecular multiple hydride transfer to CO2 by the multinuclear catalyst. It is worth noting that methanol was generated catalytically, even at low pressure and low temperature(30 °C, 5 MPa (TON 2.0) and 0.5 MPa, 70 °C (TON 3.0)). A final turnover number of 113 was obtained on recycling of the catalyst at 60 °C and 4 MPa of H2/CO2 (3:1). This catalytic system opens the door to new possibilities for hydrogenation of CO2 to methanol under mild reaction conditions and heterogenous catalysis of molecular catalyst.

CO2 hydrogenation to methanol using dinuclear iridium catalysts under gas-solid phase conditions

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.