A mineral and some light can turn carbon dioxide into a cleaning agent

Chemists are constantly hunting for ways to make carbon dioxide (CO₂) into more useful, carbon-containing substances. But one of the central problems with carbon dioxide is that it’s such a stable molecule: it’s hard to get it to react with anything.

A team of Japanese chemists has found a way to turn CO₂ into formic acid, which – aside from being a useful cleaning agent and preservative – is a key chemical ingredient in a vast array of reactions. Formic acid also appears frequently in nature, most notably in ant and bee venom. And, most recently, it’s drawn attention as a possible way to transport hydrogen fuel.

The new method relies on the concept of “photoreduction”: using light to provide energy for CO₂ to react with something which contains hydrogen, allowing it to become formic acid (CH₂O₂, often written as HCOOH).

Photoreduction has been known to work for a while, but it needed expensive or highly complicated metal catalysts such as cobalt, nickel and metal-organic frameworks. It also mostly made carbon monoxide, or CO, rather than the hallowed formic acid.

This research, described in Angewandte Chemie, describes a new catalyst that’s much easier to come across. This catalyst is a combination of alumina (Al₂O₃) and an iron-based mineral: goethite, or FeOOH.

Not only is this catalyst completely reusable, it’s also much more selective than most of the other options, as 90% of the product it makes is formic acid.

“We wanted to explore more abundant elements as catalysts in a CO₂ photoreduction system,” says co-author Professor Kazuhiko Maeda, a researcher at the Tokyo Institute of Technology, Japan.

“We need a solid catalyst that is active, recyclable, non-toxic and inexpensive, which is why we chose a widespread soil mineral like goethite for our experiments.”

As well as light, the catalyst still needs a small amount of the much rarer ruthenium to work. For now, it’s also only been proven in a liquid solution – meaning it’s not something you can stick outside to absorb atmospheric CO₂ – yet.

Nevertheless, the researchers are excited that their simply made catalyst can react with a molecule as pesky as CO₂.

“Our study shows that the road to a greener energy economy doesn’t have to be complicated,” says Maeda.

“Great results can be attained even by adopting simple catalyst preparation methods and well known, earth-abundant compounds.”