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

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. [ABSTRACT FROM AUTHOR]