Hydrothermal reduction of CO2 captured as NaHCO3 into formate with metal reductants and catalysts

Abstract

The hydrothermal reduction of CO2 captured in aqueous solutions using metal reductants is a promising novel approach that achieves high yields of conversion and high selectivity, but it presents the limitation of the high temperatures needed for the reaction to take place. In this work, experiments combining several reductant metals (Zn, Al and Fe), catalysts (Pd/C, Ni, Cu, Fe2O3 and Fe3O4) and temperatures (200, 250 and 300 ºC) were performed to optimize the process at milder temperatures. Using Al as reductant and Pd/C as catalyst, yields as high as 38 % were obtained at 200ºC, compared with the highest yield (57 %) observed at 250 ºC. Thus a significant temperature reduction can be achieved using a suitable combination of reductant and catalyst. Using this reaction system, Pd/C as catalyst and Al as reductant, an extensive set of experiments at different times and temperatures were performed in order to determine the kinetics of the process and correlate them to a mathematical model of the process. The model correctly reproduces the experimental data with average errors lower than 5.9 %. These results demonstrate the feasibility of lower the operating temperature while maintaining the performance, when using an adequate combination of catalyst and reductant.