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.”