Water, air… clean fuels: Next Chapter

Zakaria Halime (CNRS, ICMMO) here filmed in 2018 on the ROCK beamline preparing his experiment with the help of Stéphanie Belin, left, scientist on the beamline.

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!"