Efficient hydrogenation of CO2 to formic acid in water without consumption of a base

Abstract

CO₂ hydrogenation to formic acid is full of challenges due to the high stability of both H₂ and CO₂. For a long time, unrecyclable bases had been widely used in CO₂ hydrogenation to shift the reaction equilibrium by the formation of formate, while a low turnover number (TON) was obtained in the absence of a base. Herein, an efficient method of hydrogenation of CO₂ to formic acid in water without consumption of a base is realized. The base can be easily regenerated by the transformation between imidazolium bicarbonate ionic liquid and imidazolium formate in the presence of CO₂. A TON of up to 364 249could be achieved in the CO₂ hydrogenation performed in an aqueous solution. Formic acid is isolatable with a separation yield of up to 86.8%. The catalyst and base could be recycled simultaneously and their activities remained quite well preserved in a five-cycle experiment.