Enzymatic carbon dioxide to formate: Mechanisms, challenges and opportunities

The reduction of carbon dioxide (CO2) gas into soluble formate is one of the most promising carbon neutrali-zation strategies since it facilitates simultaneous fixation of carbon dioxide and the production of green chem-icals. Compared to processes using chemical catalysts, enzymatic CO2-to-formate is attractive due to its high efficiency, excellent selectivity, and mild conditions. This review summarizes different CO2-to-formate enzymes, including formate dehydrogenase (FDH), hydrogen-dependent CO2 reductase and nitrogenase, as well as reduced nicotinamide adenine dinucleotide (NADH)-dependent and NADH-independent catalytic mechanisms. The challenges for enzymatic catalysis include high-cost sacrificial donors and low NADH regeneration efficiency. New photochemical and electrochemical NADH regeneration methods and advanced NADH-independent systems provide new opportunities to overcome these challenges. Harnessing artificial electroactive mediators and diffusive-cofactor-free systems enable more feasible and sustainable enzymatic CO2-to-formate processes. Based on the versatile performance of enzymatic catalysis, there is potential for emerging applications such as upgrading carbon through multi-enzyme cascades and whole-cell catalysis. Bulk chemical biorefineries based on formate and using CO2 as a feedstock may be possible through from FDH-containing and engineered bacteria.