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A novel enzymatic process for CO2 reduction


The enzymatic process developed by the IRIG researchers achieves similar performances to the electrochemical processes for CO2 reduction while bringing the advantages of operating in a reversible way, under mild conditions and with very low surges. These results make it possible to consider their use for CO2 reduction as well as for CO oxidation, within the framework of synthesis gas purification processes for the production of various chemical products or fuels.

Published on 10 August 2021
The quest for carbon neutrality requires the development of technologies for the transformation of CO2 and its derivatives into commodity products from low-carbon energy. In this context, the design of new efficient and environmentally friendly catalytic processes for CO2 reduction is at the heart of societal concerns. In the field of catalysis for sustainable chemistry, biocatalysts have the advantage of being highly selective and efficient under mild conditions (ambient temperature and pressure, aqueous solvents). However, despite their benefits, the cost of large-scale production of enzymes and their lack of stability still limit the development of such approaches..

This is especially true for complex redox metalloenzymes, such as Carbon Monoxide Dehydrogenase (CODH), which remains to date the most efficient catalyst for the activation of small molecules like CO and CO2. CODH has an active site that is unique in biology. It is composed of a multi-metallic NiFe4S4 center whose biosynthesis involves several molecular steps, requiring a specific multi-protein machinery which is still poorly understood. Over the last few years, IRIG researchers have studied in detail the chaperone proteins involved in this mechanism. These studies have allowed them to develop a heterologous CODH production system in which the gene of the carboxydotrophic bacterium Rhodospirillum rubrum (capable of using CO as a source of carbon and energy) is expressed in Escherichia coli. This process produces, in a single purification step, an enzyme that is as stable and active as a natural CODH. The researchers went further by immobilizing this recombinant CODH on functionalized carbon nanotubes [in collaboration with the DCM-BEA of UGA Grenoble], which allowed them to develop a bioelectro-catalytic system that is stable for several hours to achieve the inter-conversion of CO2 to CO (Figure), reaching current densities of 4.2 mA.cm2 for CO2 reduction and 1.5 mA.cm2 for CO oxidation.

Interconversion of CO2 to CO catalyzed by carbon monoxide dehydrogenase grafted onto carbon nanotubes.
© LCBM

Compared to existing electrochemical CO2 reduction processes based on molecular catalysts, this enzymatic process achieves similar performances while bringing the advantages of operating in a reversible manner, under mild conditions and with very low overpotentials. These results allow to consider their use for CO2 reduction as well as for CO oxidation, in the context of synthesis gas purification processes for the production of various chemicals or fuels.
Biocatalysis is the use of natural catalysts, such as enzymes, in an organic synthesis reaction.
A chaperone protein is a protein whose function is to assist other proteins in their maturation.

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