Co-catalyst promises energy-rich outcomes from CO2

A novel ‘co-catalyst’ system using inexpensive, easy to fabricate carbon-based nanofibre materials converts carbon dioxide to carbon monoxide, a useful starting-material for synthesising fuels. The findings have been published online in advance of print in the journal Nature Communications.

‘I believe this can open a new field for the design of inexpensive and efficient catalytic systems for the many researchers already working with these easily manipulated advanced carbon materials,’ said Amin Salehi-Khojin, University of Illinois at Chicago professor of mechanical and industrial engineering and principal investigator on the study.

Researchers have spent decades trying to find an efficient, commercially viable way to chemically reduce, or lower the oxidation state, of carbon dioxide.

Although reducing carbon dioxide is a two-step process, chemists had commonly used a single catalyst, Salehi-Khojin said in a statement. He and his colleagues experimented with using different catalysts for each step.

In previous work, Salehi-Khojin used an ionic liquid to catalyse the first step of the reaction, and silver for the final reduction to carbon monoxide. The co-catalyst system was more efficient than single-catalyst carbon dioxide reduction systems, he said.

Due to the expense of silver, Salehi-Khojin and his colleagues set out to see if a relatively new class of metal-free catalysts – graphitic carbon structures doped with other reactive atoms – might work instead.

They tried a common structural material, carbon nanofibres, which was doped with nitrogen, as a substitute for silver to catalyse the second step.

When these carbon materials are used as catalysts, the doping atoms, most often nitrogen, drive the reduction reaction. But, through study of this particular reaction, the researchers found that it was not the nitrogen that was the catalyst.

‘It was the carbon atom sitting next to the dopant that was responsible,’ said Mohammad Asadi, a UIC graduate student who is one of two first-authors of the study.

As they continued to characterise the reaction it became clear not only that carbon was catalysing the reaction, but that the co-catalyst system was more efficient than silver, showing substantial synergistic effects, Asadi said.

‘Further, one can imagine that using atomically-thin, two-dimensional graphene nano-sheets, which have extremely high surface area and can easily be designed with dopant atoms like nitrogen, we can develop even far more efficient catalyst systems,’ said Bijandra Kumar, UIC research scholar and the other first-author of the paper.

The researchers hope that their research leads to commercially viable processes for the production of syngas and even petrol from carbon dioxide.