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CO2 reduction: the catalytic cycle of an iron porphyrin catalyst deciphered!

​Using a range of spectroscopic techniques, researchers at I2BC in collaboration with ICMMO have elucidated the catalytic cycle of a bio-inspired iron porphyrin catalyst, which could form the basis of economically viable solutions for the conversion and recovery of CO2.

Published on 13 June 2024

The European Parliament has adopted a climate legislation that aims to reduce net greenhouse gas emissions by at least 55% by 2030. Reducing the use of fossil fuels will not be enough to achieve this goal. We also need to be able to capture CO2 and convert it into useful products (fuels, chemicals) using low-carbon energy. And right now, we're a long way from achieving that! 

The reduction of CO2 using molecular catalysts, based on the chemical principles of the enzymes involved in the conversion of CO2, is one of the avenues being explored. However, there is not yet an economic solution for carrying out such a reaction on a global scale. The main reasons for this are:

  • the need to use rare and expensive materials as catalysts;
  • the high energy inputs required;
  • the lack of selectivity in producing reduced forms of carbon. This is an important aspect to take into account, as it will have an impact on the development of accompanying technologies.​

The Photobiology-Photocatalysis-Photosynthesis team (I2BC/B3S), in collaboration with Professor Ally Aukauloo's team (ICMMO, Orsay), develops a family of bio-inspired iron porphyrin catalysts that are particularly promising for the electro-catalytic reduction of CO2 to CO (the starting point for the production of several products of interest), as they have the advantage of combining high reactivity and high selectivity. ​

When urea-substituted, such catalysts can be used in photocatalysis (read news ​​"New perspectives for CO2 photoreduction by iron porphyrins">). In a new study published in Angewandte Chemie, the researchers deciphered the catalytic cycle of such a catalyst using a combination of infrared spectroelectrochemistry and Raman, EPR and UV-visible spectroscopies. They discovered the Fe(II)CO catalytic intermediate and show that the CO2 activation step is shifted from the Fe(0) redox state, which is required in other iron porphyrins, to the more readily accessible Fe(I) state. This effect results from the activation of the CO2 substrate by hydrogen bonds provided by the urea groups present in the second iron coordination sphere, thereby reducing the energy required for catalysis.​

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