Catalytic conversion of NaHCO3 into formic acid in mild hydrothermal conditions for CO2 utilization

The increasing atmospheric CO2 level causes global warming and may pose catastrophic effects to the humanity. Among the various options to reduce the CO2 atmospheric loading, hydrothermal reactions may have a high potential for rapidly and effectively converting CO2 into useful chemicals. In this study, the hydrothermal conversion of CO2 into formic acid was carried out by using Fe as a reductant and Ni as a catalyst. The effect of various experimental parameters, e.g., amount of Fe (Ni), Fe/Ni ratio, temperature, reaction time, alkalinity etc. was investigated. Results showed that Ni played a catalytic role in the hydrothermal conversion of CO2 into formic acid. The highest yield of formic acid of 15.6% was achieved under optimal conditions, i.e., Fe/Ni ratio of 1:1, temperature of 300 °C, reaction time of 120 min, filling rate of 35% and NaHCO3: Fe of 1:6. Additionally, the selectivity of formic acid was more than 98%. It was also found that the hydrothermal conversion could not occur without either the addition of catalyst or the existence of CO2 when Fe was used as a reductant. The role of CO2 in the hydrogen production was discussed.