Another new method to convert carbon dioxide into useful products

Chemists have developed a new catalytic method to transform carbon dioxide into formate, a chemical compound with many uses from pesticides to preservatives.

The team, led by researchers at Yale University in the US, say this method could help remove carbon dioxide (CO₂) from the atmosphere, and provide a new pathway to create useful chemical compounds that otherwise would be made from fossil fuels.

“Most of our fuels and commodity chemicals are currently derived from fossil fuels,” says Nilay Hazari, chemist at Yale and co-author of the new research. “Their combustion contributes to global warming and their extraction can be environmentally damaging. Therefore, there is a pressing need to explore alternative chemical feedstocks.”

Catalysing CO₂ conversion

Converting CO₂ into usable products on an industrial scale is tricky. The problem lies in catalysts: substances which enable and speed up chemical reactions. Often, these substances also allow the reactions to happen at lower temperatures or in different conditions.

Most industrial chemicals – from plastics to fertilisers to pharmaceuticals – are made using catalysts. But these often only work under extreme temperatures or pressures, and are not as stable or productive as desired. As the world decarbonises, we will need more new catalysts, especially those that can work under milder conditions.

Catalysts usually fall into two main classes: homogenous (which is in the same phase as the reactant, e.g. gas, and is more selective) and heterogenous (which is in a different phase and thus can be easily separated from the reaction mixture, and is more stable but less selective).

This new study focused on a third, lesser-studied catalytic class called immobilised catalysts. These involve catalysts that are fixed in one position to a solid support, which allows for them to be easily separated and reused.

In principle, this class could combine the benefits of both heterogenous and homogenous catalysts.

The era of new catalysts

The paper, recently published in the journal Chem, explored using immobilised catalysts to transform CO₂ into formate.

The team attached molecular manganese catalysts to a support made up of semi-conducting, porous silicon. Other research had previously looked at using porous silicon, showing that modifying its surface could help fine-tune the process of catalysis.

In this study, the team coated the silicon with a thin oxide layer. When exposed to light, the silicon transferred electrons to the catalyst, which in turn triggered the CO₂-to-formate reaction.

“Formate is a very appealing product, as it is a potential stepping-stone to materials used industrially in very large quantities,” says Yale chemist and co-author, James Mayer.

Formate, or formic acid, has many industrial applications, including as a preservative and antibacterial agent in livestock feed; as a pH adjuster in cosmetic products; as a pesticide and herbicide; and in processing textiles and leather. Research is also underway into formic acid fuel cells.

This catalyst may also be useful to facilitate reactions with materials other than CO₂.