A metal-free catalyst developed at Université Laval can reduce carbon dioxide (CO2) to methanol using borane (BH3) as a source of hydrogen. The system is one the most efficient yet developed for CO2 reduction and is an important step toward being able to transform this greenhouse gas from a pollutant into a raw material for commodity chemicals.

Various ways of reducing CO2 to more useful species are already known, but most rely on transition metal-based catalysts that are still relatively inefficient. A team lead by Laval chemistry professor Frédéric-Georges Fontaine has been working on an alternative approach. “Carbon is electrophilic, and oxygen is nucleophilic,” says Fontaine. This means that the linear CO2 molecule can be bent and activated by molecules with Lewis acids at one end and Lewis bases at the other. Such molecules, often called frustrated Lewis pairs (FLPs), have been shown to bind CO2, but most do so quite strongly, meaning they can’t let it go to complete the reduction.

In a paper published in the Journal of the American Chemical Society, Fontaine showed that a molecule with mildly Lewis acidic groups on one end and mildly Lewis basic groups on the other attracted CO2 well enough to bend the molecule, but not so much that it couldn’t be released. It readily catalysed the reaction of CO2 with BH3 adducts to form molecules that easily hydrolyze into methanol. “The fastest one we’d previously seen was a nickel complex that reached 500 reaction turnovers per hour,” says Fontaine. “We can go over 800 reactions per hour.”

Of course, hydrogen gas is a much cheaper source of hydrogen than BH3. Could the same system work with H2? “We believe that there is a way of doing it,” says Fontaine. “But it won’t be easy, and it’s probably still a few years until that becomes a reality.”