HIGHLY OXYGEN-STABLE CO_2 REDUCTASE-CATALYZED BYCONVERSION OF CARBON DIOXIDE INTO FORMATE IN ELECTROCHEMICAL REACTOR

摘要

Electrochemical reduction of carbon dioxide (CO_2) into value-added chemicals have been one of promising issues to utilize greenhouse gas for the storage of hydrogen, bioplastic, fuel cell et al. Among many potential candidates such as formate, alcohols, ethylene, etc., formate was known one of most promising chemicals through the addition of two elections and one proton during electro-catalytic reduction of CO_2. Here, our group has developed efficient CO_2 reductase-catalyzed conversion of CO_2 into formate in electrochemical reactor. Electro-biocatalytic reduction of CO_2 into formate have three main challenges. Formate dehydrogenase(FDH) have been one of potential CO_2 reductase candidates but the activity of many FDHs for formate oxidation was superior than that of CO_2 reduction. However, recombinant MeFDH1 in our study showed significantly higher preference for CO_2 reduction with 209 (±10.66) s~(-1) of turnover rate than that of formate oxidation with 85.62 (± 5.76) s~(-1). In addition, the value of kinetic equilibrium constant (Keq), which determines the direction of reaction in reversible catalysis, implied that kinetic preference for CO_2 reduction is 62.3-folds higher than that for formate oxidation. This kinetics analysis allowed MeFDHI to be referred to as the CO_2 reductase. As another challenge, Mo- or W-containing formate dehydrogenase was known vulnerable against oxygen molecule. As contrasted with the high oxygen-sensitivity of FDHs from other strains, MeFDHI was not deactivated even under 0.13 mM of dissolved oxygen. At a range of oxygen level (0.1 % to 4 %) in the composition of Carbon Capture and Storage (CCS) gas, MeFDHI was consequently stable without considerable decreased activity. Lastly, the long-term stability of CO_2 reduction reaction system has been indispensable issue in both biocatalysts and chemical catalysts. Through the immobilization of MeFDHI, the enhanced stability for long-term operation leaded the formate formation over 500 mM with high volumetric productivity for several days.