Water, air… and clean fuels
Over 40 billion tons of CO2 are emitted every year due to human activities. What can we do with this waste?
In Nature, plants capture CO2 and transform it into plant material (biomass) thanks to solar energy. It’s photosynthesis.
At the Institut de Chimie Moléculaire et des Matériaux (Orsay), the scientific team called « artificial photosynthesis » is inspired by this natural phenomenon in order to transform CO2, not into biomass but into clean fuels such as methanol or methane. In 2018 this team came to SOLEIL, at the ROCK beamline, to find out what are the best catalysts of the chemical transformation of CO2, that is to say the compounds that will achieve this artificial photosynthesis quickly and efficiently.
Autumn 2024: a look back at this research
Eliminating the CO2 that saturates our atmosphere... An ecological Holy Grail that many scientists are persistently striving to reach. This is the case for Zakaria Halime, a chemist who is exploring every possible way to transform undesirable carbon dioxide—particularly into CO, carbon monoxide. While this gas is feared when it leaks from our boilers, it is actually a key component in a wide range of industries. Hundreds of thousands of tons of it are produced annually to manufacture methane, methanol, hydrocarbons, or even acetic acid.
Zakaria Halime has valuable allies to break down the CO2 molecule: catalysts—such as iron porphyrins—that enhance and accelerate the chemical reaction. In 2018, alongside Benedikt Lassalle, a scientist at the synchrotron SOLEIL, he developed a new spectroscopy method to observe in real time, using X-rays, the reduction of CO2 into CO. This method relies on an electrochemical cell placed on the ROCK beamline at SOLEIL. The method proved effective, resulting in a first publication (1).
Subsequently, Zakaria made the catalytic system that breaks down CO2 even more flexible. The chemist is now able to fine-tune the very structure of the catalyst to give it the desired qualities for a specific application. For instance, to achieve a more energy-efficient reaction, a faster reaction, or even a reaction that remains effective when CO2 is present in low concentrations. In short, a kind of "Swiss army knife" catalyst that adapts to various objectives (2).
Once again, with Benedikt Lassalle, Zakaria tested a new approach using the LUCIA beamline. Instead of allowing the reaction to occur in an organic solvent, as is usually the case, they deposited the catalyst on a modified electrode. The CO2 was then reduced in water, quite simply. This process presents highly interesting advantages for industry: the final product can be collected in water instead of requiring extraction from an organic mixture, and the reaction can be scaled up (3).
However, the relentless quest for effective methods to convert CO2 into CO can interest sectors beyond energy, such as the pharmaceutical industry. During the validation process of a new drug, it is common to "radio-label" it—introducing a slightly radioactive marker to track the distribution of the active molecule in the body. Eighty percent of drugs go through this little-known stage before being marketed. In 2023, Zakaria Halime proposed an innovative concept for radio-labeling. First, by using CO2 in which the carbon is slightly radioactive (either "carbon-13" or "carbon-14" instead of the most abundant "carbon-12"). Then, by reducing this CO2 into CO while preserving its radioactivity. Finally, by inserting this CO into the active molecule, thus producing a "labeled" drug. This original idea resulted in a publication in the prestigious journal Nature (4).
Amidst this rich and complex nebula of chemical reactions, Zakaria anticipates once again turning to the synchrotron in the future: "Real-time X-ray spectroscopy is an important tool. I'm in almost constant dialogue with Benedikt Lassalle, and that won’t be ending anytime soon!"
Related publications
(1) Cheaib, K., Maurice, B., Mateo, T., Halime, Z., Lassalle-Kaiser, B. "Time‐resolved X‐ray absorption spectroelectrochemistry of redox active species in solution" Journal of Synchrotron Radiation., 26(6): 1980-1985. (2019).
(2) P. Gotico, L. Roupnel, R. Guillot, M. Sircoglou, W. Leibl, Z. Halime, A. Aukauloo "Atropisomeric Hydrogen Bonding Control for CO2 Binding and Enhancement of Electrocatalytic Reduction at Iron Porphyrins" Angew. Chem. Int. Ed. , 59, 22451–22455 (2020).
(3) Zhang, C., Dragoe, D., Brisset, F., Boitrel, B., Lassalle-Kaiser, B., Leibl, W., Halime, Z., Aukauloo, A. "Second-Sphere Hydrogen-Bonding Enhances Heterogeneous Electrocatalytic CO2 to CO Reduction by Iron Porphyrin in water" Green Chemistry., 23(22): 8979-8987. (2021).
(4) S. Monticelli, A. Talbot, P. Gotico, F. Caillé, O. Loreau, et al.. "Unlocking full and fast conversion in photocatalytic carbon dioxide reduction for applications in radio-carbonylation". Nature Communications 14 (1), pp.4451 (2023).
-------------------------------------------
Audio Transcription
VOICE-OVER
Factories and vehicles are emitting ever more carbon dioxide into the atmosphere.
Over 40 billion tons of CO2 are emitted every year due to human activities.
How should we react to the situation? What can we do with this waste?
Zakaria Halime - chemist and CNRS researcher - Institut de Chimie Moléculaire et des Matériaux d'Orsay
Today, several laboratories are researching solutions that will both capture CO2 that is reaching rather high concentrations in our atmosphere, and transform this CO2 into added-value molecules.
VOICE-OVER
Nature has the solution. It achieves this task using photosynthesis. Plants can actually capture CO2 and transform it, thanks to solar energy, into plant material or "biomass".
A concept that has set researchers thinking about new approaches.
Zakaria Halime
There is a small team called "artificial photosynthesis" that is inspired by all the steps of photosynthesis to achieve our aim, which is to use light energy to transform CO2, not into biomass but rather into clean fuels such as methanol or methane.
VOICE-OVER
There is a downside, however: the carbon dioxide molecule is highly resistant to any transformation. And that is because the bonds between the carbon and oxygen atoms are very... very strong.
In order to break them, researchers need the help of a catalyst.
It was just this challenge of finding THE ideal catalyst - the compound that will achieve this artificial photosynthesis quickly and efficiently- that inspired Zakaria Halime to work with Benedikt Lassalle on the ROCK beamline of the SOLEIL synchrotron.
Benedikt Lassalle - chemist and beamline scientist - Synchrotron SOLEIL
We will be looking at iron porphyrins.
Zakaria Halime
... bio-inspired catalysts, because this type of complex -or molecule- is already used by nature.
Benedikt Lassalle
These catalysts are promising enough but people are seeking to improve them.
In order to do so, we have to be able to understand the reaction mechanism, how the catalytic cycle occurs, and what the structure of these catalysts is.
VOICE-OVER
During the reaction, the catalyst will try to "capture" the CO2 molecule and to "tear away" its oxygen atoms. These exchanges between the catalyst and the CO2 molecule can be monitored by X-ray spectroscopy.
Benedikt Lassalle
Quite often, the catalysts are observed before and possibly after the reaction, but we are trying to watch them during the CO2 reduction reaction to have an idea of their structure when they are active.
Zakaria Halime
We have a reaction that occurs very quickly, there are hundreds of thousands of reactions per second. And we are going to try and take photos during a cycle.
But you also need enough of these photos, to retrace the whole story.
Benedikt Lassalle
So it is all these steps, during catalysis, that we are going to try and watch by using the time resolution available on the ROCK beamline.
VOICE-OVER
A solution containing CO2 and the catalyst will circulate in an "electrochemical cell" especially designed on a 3D printer for the experiment.
That is where the X-rays will probe the material states and will provide the researchers with valuable information on the catalyst's operating mode.
The very detailed analysis of this chemical transformation is essential for any attempt to improve the catalyst's efficiency. Making it more selective and faster and reducing its energy consumption. Because the aim is to be able to obtain fuel thanks to solar energy alone.
Benedikt Lassalle
We can already reduce CO2 into CO reasonably well. But it isn't a target that is industrially or economically very interesting. Methane is much more interesting.
If we could make methanol, ethanol and other chemical compounds or fuels with a higher added value, that would be interesting.
VOICE-OVER
There is still a long way to go to successfully match nature's ingenuity; to capture CO2, and to do so effectively. Because industry needs time. Several decades of research are undoubtedly still necessary to obtain clean fuels or "zero emissions".
Zakaria Halime
The research we are doing today won't totally solve the problem.
We are looking for ways to capture and transform CO2.
But that shouldn't stop us from reducing our consumption of fossil fuel.