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

Abstract

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 Pd_0.5Cu_0.5/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 Pd_0.5Cu_0.5/C for methanol activation.