Hydrogen-fueled CO₂ reduction using oxygen-tolerant oxidoreductases

Area of Science:

• Biocatalysis
• Sustainable Chemistry
• Enzyme Engineering

Background:

• Hydrogen gas is a promising alternative fuel, but its efficient conversion is hindered by oxygen sensitivity in key enzymes.
• Formate production from hydrogen (H2) and carbon dioxide (CO2) using hydrogenase (H2ase) and formate dehydrogenase (FDH) offers a stable storage solution.
• Oxygen contamination in low-cost H2 sources severely damages conventional H2ase and FDH enzymes, limiting practical applications.

Purpose of the Study:

• To develop an oxygen-tolerant enzymatic cascade reaction for converting H2 and CO2 into formate.
• To identify and utilize robust H2ase and FDH enzymes capable of functioning in the presence of oxygen.
• To enable the sustainable production of formate from readily available H2 and CO2 sources.

Main Methods:

• Investigated a pair of oxygen-tolerant enzymes: H2ase from *Ralstonia eutropha* H16 (ReSH) and FDH from *Rhodobacter capsulatus* (RcFDH).
• Established a cascade reaction system combining ReSH and RcFDH for H2 and CO2 conversion.
• Implemented *in situ* regeneration of NAD+/NADH cofactor to sustain the enzymatic reaction in an oxygen-containing environment.

Main Results:

• Successfully achieved a cascade reaction converting H2 and CO2 to formate using ReSH and RcFDH.
• Demonstrated the operational stability and efficiency of the chosen enzymes in the presence of oxygen.
• Validated the *in situ* cofactor regeneration system for continuous formate production.

Conclusions:

• Developed a novel, oxygen-tolerant enzymatic process for sustainable formate production.
• Overcame the critical limitation of oxygen sensitivity in H2ase and FDH enzymes.
• Paved the way for utilizing low-cost, potentially oxygen-containing H2 sources for formate synthesis and storage.