New way to turn CO2 back into petrol as ‘carbon-neutral fuel’

It might sound like a step backwards, but US scientists have worked out a way to turn carbon dioxide (CO2) captured from the air or from power plants into fuel that is ‘basically petrol.’

Carbon capture and storage (CCS) is one of the new technologies that researchers at Stanford University hope will play an important role in tackling the climate crisis.

It involves the capture of CO2 from burning of fossil fuels in power generation (or from the air), and the new Stanford process can turn captured carbon into propane, butane or other hydrocarbon fuels.

The scientists hope that in the long run, the process can create a fuel which can be used, captured, then used again – and may unlock innovative processes which would allow captured CO2 to be turned into a solid and buried.

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Matteo Cargnello, a chemical engineer at Stanford University, said: “We can create gasoline [petrol], basically.

"To capture as much carbon as possible, you want the longest chain hydrocarbons. Chains with eight to 12 carbon atoms would be the ideal.”

A new catalyst, invented by Cargnello and colleagues, moves toward this goal by increasing the production of long-chain hydrocarbons in chemical reactions.

It produced 1,000 times more butane – the longest hydrocarbon it could produce under its maximum pressure – than the standard catalyst given the same amounts of carbon dioxide, hydrogen, catalyst, pressure, heat and time.

The new catalyst is composed of the element ruthenium – a rare transition metal belonging to the platinum group – coated in a thin layer of plastic.

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Ruthenium also has the advantage of being less expensive than other high-quality catalysts, like palladium and platinum.

The ability of the new catalyst to produce petrol from the reaction is a breakthrough, said Cargnello.

Petrol is liquid at room temperature and, therefore, much easier to handle than its gaseous short-chain siblings – methane, ethane and propane – which are difficult to store and prone to leaking back into the skies.

Cargnello and other researchers working to make liquid fuels from captured carbon imagine a carbon-neutral cycle in which CO2 is collected, turned into fuel, burned again and the resulting carbon dioxide begins the cycle anew.

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Lead student author Chengshuang Zhou, a doctoral candidate in Cargnello’s lab, said: "An uncoated catalyst gets covered in too much hydrogen on its surface, limiting the ability of carbon to find other carbons to bond with.

“The porous polymer controls the carbon-to-hydrogen ratio and allows us to create longer carbon chains from the same reactions.”

Cargnello is also working on other catalysts and similar processes that turn carbon dioxide into valuable industrial chemicals, like olefins used to make plastics, methanol and the holy grail, ethanol, all of which can sequester carbon without returning carbon dioxide to the skies.

“If we can make olefins from CO2 to make plastics. We have sequestered it into a long-term storable solid. That would be a big deal," he said.

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