Recycling carbon dioxide would reduce its atmospheric buildup, one of the main causes of global warming. Photo-catalysis approaches directly inspired by natural photosynthesis could help chemists meet this great challenge. However, there are many unresolved issues that must be addressed to overcome this challenge. For several years, Winfried Leibl's team (B3S/I2BC) has been developing, in collaboration with Prof. Ally Aukauloo's team (ICMMO, Orsay), a family of bio-inspired iron porphyrin catalysts that are particularly promising for the catalytic electro-reduction of CO2.
In order to exploit solar energy more directly, the researchers used their catalyst, consisting of an iron porphyrin decorated with urea functions (UrFe), acting as a scaffold of multiple hydrogen bonds stabilizing the CO2 substrate (see Joliot news), coupled to a photo-chromophore to drive the reaction by light. They succeeded in obtaining a spectacular catalytic activity for the photoreduction of CO2 to CO in the presence of the porphyrin UrFe, which greatly surpasses the activities obtained with iron porphyrins without urea groups. To explain this unprecedented result, mechanistic studies were conducted to elucidate the key steps of the light-induced reaction : they highlight a different pathway in the case of UrFe porphyrin that allows the reaction to proceed in a single electron transfer step to form the active state of the catalyst capable of binding CO2, instead of two steps.
This work revealed that the UrFe porphyrin catalysts previously developed by the team for the electrocatalysis of CO2 can be successfully employed in a photocatalytic approach. The unprecedented improvement in activity thus obtained constitutes a new paradigm in the catalytic reduction of CO2.
This study, illustrated on the cover of the journal Angewandte Chemie of March 9, 2022 (vol. 61 n°14), was also the subject of a Very Important Paper (VIP) in this journal.
Contacts : Winfried Leibl (winfried.leibl@cea.fr); Ally Aukauloo (ally.aukauloo@universite-paris-saclay.fr)
* ICMMO : Institut de Chimie Moléculaire et des Matériaux d'Orsay
** ISMO : Institut des Sciences Moléculaires d'Orsay
-A catalyst accelerates a chemical reaction, minimizing the energy required for the reaction, and is not consumed during the reaction, thus constituting a sustainable process.
-An iron porphyrin is a molecule with a macrocyclic structure, like the heme in hemoglobin, which is used to bind oxygen in red blood cells.