Molecular H2O promoted catalytic bicarbonate reduction with methanol into formate over Pd0.5Cu0.5/C under mild hydrothermal conditions

Direct reduction of bicarbonate, a typical product of CO2 captured in alkaline solution, into value-added organics is one promising way to achieve a simplified and green CO2 capture and utilization process. In this work, a new strategy of bicarbonate reduction coupled with methanol oxidation into a dual formation of formate under mild hydrothermal conditions is reported. A 68% formate production efficiency based on the reductant methanol and nearly 100% selectivity of formate were obtained via a Pd0.5Cu0.5/C catalyst at 180 °C. An operando hydrothermal ATR-FTIR study proved that the bicarbonate was reduced by the in situ generated hydrogen from methanol, which was stepwise oxidized to formaldehyde and formic acid. Notably, DFT calculations and a qNMR study of the 13C and 2H (D) isotopic labelling revealed that H2O molecules not only supplied the hydrogen for bicarbonate reduction but also acted as an indispensable promoter to enhance the catalytic performance of Pd0.5Cu0.5/C for methanol activation.