Seeking the magic molecule
All roads lead to Rome—a notion that also applies to the field of chemistry. And so Benjamin List and his team at the Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr are exploring several pathways in their endeavour to implement his innovative idea—the photocatalytic reduction of CO2.
How to go about approaching a revolutionary idea that quite possibly has never been studied before? It’s a question that Benjamin List from the Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr has been pondering since the start of 2025—and the start of his WSS project, in which he’s aiming to employ photocatalytic reduction to split carbon dioxide (CO2) into pure carbon (C) and oxygen (O2). Should he succeed, the reaction could be used to reverse engineer excess atmospheric CO2 generated by human activities.
In this kind of novel, high-risk undertaking, it’s advisable to not put all one’s research eggs into one basket. Which is why Benjamin List is building a team of scientists with the expertise to explore three main lines of inquiry. The first two—homogeneous and heterogeneous catalysis—stem from classical chemistry, while the third explores whether biological organisms or enzymes could be used to split CO2 molecules.
In homogeneous catalysis, the researchers are focusing on reactions enabled by small, organic molecules. In other words, they’re seeking the type of catalysts Benjamin List used for his groundbreaking research on organocatalysis—the work that led to his Nobel Prize. List says that he’s therefore doing an important part of the work himself: “In the mornings, when it’s quiet in my office, I design possible catalysis cycles for the reaction.”
These ideas then travel halfway round the globe to Hokkaido University in Japan, where a small team led by Professor Satoshi Maeda has been collaborating with Benjamin List for many years. “Our colleagues in Japan are highly gifted theoreticians,” List says. “They make calculations for each catalysis cycle to determine whether it can function.” One advantage in this work is the fact that CO2 is a small molecule; with larger molecules and catalysts, computer-assisted methods quickly hit their limits.
Identifying helpful metals
The second line of investigation—heterogeneous catalysis—deals with the development of metal-based catalysts. “We found a publication that claims germanium oxide can be used to remove oxygen from CO2,” List relates. “We’re currently trying to reproduce the method.” In addition, two new team members are studying other interesting metal oxides that could prove useful.
Comparable procedures have already been developed for several steps needed in the heterogeneous approach. For instance, German chemicals company BASF is investigating ways to break methane down into hydrogen and solid carbon, as List explains. In these experiments, methane gas is conducted through hot, liquid tin. The hydrogen escapes as a gas, while the coal is deposited on the tin. To prevent the coal from deactivating the catalyst, it’s periodically removed using a device akin to a windscreen wiper. “Our system will follow a similar principle,” List explains.
Coal biology
The project’s third line of inquiry is without precedence in research. Indeed, it represents an entirely new kind of biology, one involving the development of biological catalysts—preferably living cells that absorb CO2 from the air and precipitate carbon in its elemental form. List says the idea is less utopian than it perhaps sounds. After all, plants have been performing photosynthesis to generate carbohydrates from CO2, and that for millions of years. “Our reaction is just missing the final step of cleaving water from carbohydrates.”
One challenge in accomplishing this decisive step is that the mechanism apparently doesn’t occur in nature. “We’ve found just one publication in which a team described how single-cell organisms, so-called archaea, may produce elemental carbon,” List relates. “However, we need to determine whether the information is accurate.”
Excavations in the coal pit?
The researchers remain undaunted by the many unknowns: they’ll seek enzymes and test them for their viability as biological catalysts, and List plans to explore whether biological coal sources might be found after all. “For example, it would be interesting to cultivate and test bacteria from coal mines,” he says. This, because the cleavage of water from plant matter also occurs in natural coal formation. “How this happens exactly, however, is a mystery to be solved.”
Because establishing all three lines of inquiry will take time, Benjamin List has decided to broaden the project’s focus to include something more readily achievable. He believes it’s relatively easy to produce furans from cellulose and lignin, the main components of wood. The only problem is that there are no practicable methods for transforming this substance group into high-value chemical compounds. At present, one of his PhD students is studying these types of reactions—with both great relish and success, as List relates, adding: “We want to build on that success.” And although these processes aren’t yet the soughtafter “perfect chemical reaction” of splitting CO2, he points out that the findings could help pave the way towards a bio-based chemical industry.
