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Copper clusters capture and convert carbon dioxide to make fuel

08 August 2015

Chemical reactions that make methanol from carbon dioxide rely on a catalyst, and Argonne scientists have identified a new material that could fill this role.`

A copper tetramer catalyst consists of small clusters of four copper atoms each, supported on a thin film of aluminium oxide (Image: Larry Curtiss/Argonne National Laboratory)

With its unique structure, this catalyst - a copper tetramer - can capture and convert carbon dioxide in a way that ultimately saves energy. It consists of small clusters of four copper atoms each, supported on a thin film of aluminium oxide.

These catalysts work by binding to carbon dioxide molecules, orientating them in a way that is ideal for chemical reactions. The structure of the copper tetramer is such that most of its binding sites are open, which means it can attach more strongly to carbon dioxide and can better accelerate the conversion.

The current industrial process to reduce carbon dioxide to methanol uses a catalyst of copper, zinc oxide and aluminum oxide. A number of its binding sites are occupied merely in holding the compound together, which limits how many atoms can catch and hold carbon dioxide.

"With our catalyst, there is no inside," says Stefan Vajda, a senior chemist at Argonne National Laboratory. "All four copper atoms are participating because with only a few of them in the cluster, they are all exposed and able to bind."

To compensate for a catalyst with fewer binding sites, the current method of reduction creates high-pressure conditions to facilitate stronger bonds with carbon dioxide molecules. But compressing gas into a high-pressure mixture takes a lot of energy.

The benefit of enhanced binding is that the new catalyst requires lower pressure and less energy to produce the same amount of methanol.

Copper tetramers could allow us to capture and convert carbon dioxide on a larger scale,reducing an environmental threat and creating a useful product like methanol that can be transported and burned for fuel. However, there are potential obstacles to progress.

There's a chance that copper tetramers may decompose when put to use in an industrial setting, so ensuring long-term durability is a critical step for future research. And while the scientists needed only nanograms of the material for this study, that number would have to be multiplied dramatically for industrial purposes.

Meanwhile, the researchers are interested in searching for other catalysts that might even outperform their copper tetramer.

A paper describing this work is published in The Journal of the American Chemical Society.

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