Abundant ingredients make CO₂ reduction more practical

To make it practical to transform CO₂ into something more useful, researchers are trying to develop catalytic reactions that use cheap and abundant ingredients. Robert J. Gilliard Jr. and coworkers at the University of Virginia and Latrobe University have uncovered a key step in this process, unlocking electrons from CO₂’s strong π-bonds by binding them to cyclic (alkyl)(amino)carbenes (ChemRxiv, 2020, DOI: 10.26434/chemrxiv.12665336.v1). They then used three earth-abundant alkali metals to reduce the stubborn CO₂ bond. ChemRxiv is a preprint server and the paper has not been peer reviewed.

“CO₂ by itself does not react with things like alkali metals,” Gilliard says. Once the carbene forms a zwitterionic adduct with the CO₂, the researchers add solid lithium, sodium, or potassium to form alkali metal clusters. Depending on how much metal they add, the CO₂ is either singly or doubly reduced. The process works at atmospheric temperatures and pressures, sidestepping the need for hard-to-handle or expensive reagents or catalysts. The resulting clusters’ valence orbitals aren’t completely filled and they have interesting reactivities. Using earth-abundant metals for this reaction makes it more applicable for future CO₂ reduction technologies, Gilliard says.

The approach is unique and beautiful in its simplicity, says Robert Mulvey, an inorganic chemist at the University of Strathclyde. The chemistry can lead to high-value chemicals and materials such as methanol and dimethyl ether. It’s also a remarkable example of how broadly chemists can apply these types of carbenes, according to Guy Bertrand, an organometallic chemist at the University of California San Diego. “These results should encourage chemists to develop catalysts based on carbon rather than on transition metals,” he says.