CO₂ hydrogenation to formate by immobilized formate dehydrogenase: Challenges and opportunities

Carbon dioxide (CO₂) conversion to valuable chemicals has recently been considered as a better alternative to conventional CO₂ remediation processes. Formate dehydrogenase (FDH) is a biocatalyst that can convert CO₂ to formate in a one-step hydrogenation reaction at mild conditions. Enzymatic CO₂ hydrogenation has several advantages over the conventional chemical catalyst-based processes that are toxic and involve the formation of toxic byproducts. Nevertheless, the enzymatic approach has yet to be implemented at an industrial level, due to the poor stability of the enzyme at long term repeated uses and slow reaction kinetics. Another major challenge that prevents industrial application of FDH is the dependence on costly cofactor NADH as source of hydrogen. Each mole of formate produced consumes an equal amount of NADH, which is oxidized to NAD. The produced NAD is a potent inhibitor of FDH and its accumulation within the system leads to reverse reaction of formate oxidation to CO₂. The kinetics of reaction can be accelerated by the addition of enzyme carbonic anhydrase (CA) to the system. The operational stability and reusability of FDH can be improved by immobilization of enzymes on a suitable support material. Whereas the NADH problem can be eliminated by coupling the hydrogenation reaction with a cofactor regeneration system within the reactor. A proper choice of the support material and the regeneration system are therefore crucial for maintaining the stability and activity of FDH for repeated use. The efficiency of CA and types of cofactor regeneration systems on the activity of immobilized FDH on various support materials are summarized in this work. The future of formic acid synthesized by enzymatic CO₂ hydrogenation is also discussed.