How to recycle CO2 from flue gases

Unlike often under laboratory conditions, CO₂ makes up only a small proportion of the gas mixture in flue gases or the atmosphere. In order to extract it under realistic conditions and reuse it as a valuable material, catalysis processes must therefore also work when the CO₂ concentration is low. 

Preventing competitive reactions

“Our problem is the competitive reactions that take place at the catalyst,” explains Wolfgang Schuhmann. “The fewer CO₂ molecules there are to convert, the more likely it is that hydrogen will be produced during catalysis instead of the desired product.” If you adjust the electrolyte and choose a more alkaline solution to prevent this, you have a different problem: CO₂ is converted to carbonate and is no longer available for the desired reactions. 

Successful catalytic processes for CO₂ reduction have already been described down to a CO₂ carbon dioxide content of 10 to 20 percent. But what if the content is even lower? “By using a superactive catalyst based on nickel-copper, we were able to successfully catalyze the reduction down to a CO₂ content of five percent,” says Adib Mahbub, the first author of the publication. Below this level, the researchers had to reach into their bag of tricks: By adjusting the electrical potentials and the electrolyte, it was then even possible to carry out the reduction from a gas mixture with just two percent CO₂. “Although this means a loss of energy, clever process control allows us to access sources for the first time that we were previously unable to use for CO₂ reduction,” says Wolfgang Schuhmann. “Future generations will have to build on such concepts if they want to extract CO₂ from the atmosphere, where the CO₂ content is even lower.