Acetogenic Conversion Of H-2 And Co2 Into Formic Acid And Vice Versa In A Fed-Batch-Operated Stirred-Tank Bioreactor

Currently one of the biggest challenges for society is to combat global warming which requires the implementation of CO2 mitigation strategies as well as strategies to replace fossil-fuel-based energy carriers. Since formic acid is considered as a liquid organic hydrogen carrier which directly addresses major challenges in the field of energy storage and (bio)chemical production, the formate bioeconomy and its popularity are rapidly growing. In this study, we describe a biological route for the storage of H-2 and the capturing of CO2 in the compound formic acid using acetogenic bacteria as catalysts. The biocatalysis was proven in batch-operated stirred-tank bioreactors, demonstrating the technical feasibility of upscaling of the established whole-cell system. The process showed an efficiency of 100% for CO2 conversion, and formic acid production proceeded with a specific rate of 48.3 mmol g(-1) h(-1). Notably, no other products were coproduced in the process. The reverse reaction, H-2 production from formic acid, was also possible with a qH(2) of 27.6 mmol g(-1) h(-1). The determined turnover frequency and turnover number underline the potential of acetogenic bacteria as biocatalysts for the two challenging reactions of CO2 hydrogenation and H-2 evolution from formic acid.