New Way to Turn Carbon Dioxide into Coal Could "Raise Emissions Clock" | Science



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A liquid metal catalyst converts carbon dioxide to solid carbon.

Peter Clarke / RMIT University

By Robert F. Service

If humans hope to limit global warming to only 2 ° C of warming, we have a lot of work to do, say scientists: reduce emissions, plant trees and purify carbon dioxide (CO2) from the sky with the latest technologies. Now a new process can convert gaseous CO2– the product of the combustion of fossil fuels – solid carbon at room temperature, using only a net of electricity. But making it work on a global scale will be a formidable challenge.

In recent years, researchers have discovered a handful of solid-metal catalysts, compounds that accelerate chemical reactions, capable of converting CO2 in solid carbon. But these only work at more than 600 ° C, and so the heat requires a lot of energy – and money. Catalysts also accumulate rapidly when the carbon they produce accumulates, limiting their ability to maintain reactions.

To solve this problem, chemists Dorna Esrafilzadeh and Torben Daeneke of RMIT University in Melbourne, Australia, have turned to a new class of catalysts based on liquid metal alloys at room temperature. One of these catalysts, reported for the first time in Nature Chemistry in 2017, consists of catalytically active palladium mixed with liquid gallium. (The liquid allows palladium to continuously convert low value hydrocarbons called alkanes into higher value alkenes, without gumming.) Esrafilzadeh, Daneneke and their colleagues wanted to know if a similar product would work with CO.2.

They first made an alloy of gallium, indium and tin that is liquid at room temperature and conducts electricity. They enriched the silver mixture with a pinch of catalytically active cesium and placed it in a glass tube, with a squirt of water favoring the reduction of CO emissions.2 convert to carbon.

When they inserted a wire into the liquid metal, a portion of the cesium located at the top of the liquid surface reacted with oxygen from the ambient air, forming an ultrafine layer of water. cesium oxide. But most of the cesium remains protected by the liquid metal. Then the researchers channeled pure CO2 in the glass tube and sent a jolt of electricity into the wire. CO2 diffused into the liquid metal where cesium metal and electricity had converted it to solid carbon, Esrafilzadeh and his colleagues reported today in Nature Communications.

The researchers say that the exact mechanism of the reaction is not yet clear, but it probably involves five separate steps, since cesium interacts with oxygen, CO2and water, finally releasing solid carbon and pure oxygen as by-products. The major advantage of this new approach is that the cesium catalyst does not gum. Instead, the carbon forms small black flakes on the liquid metal surface that then break off and move to the sides and bottom of the tube, allowing the catalytic reaction to continue.

Bert Weckhuysen, a chemist at the University of Utrecht in the Netherlands, describes this work as "new" and "rather pleasant". He states that the carbon produced could be used in a wide variety of materials, such as battery electrodes, tennis rackets and golf. clubs and wings of plane.

The big advantage, however, would be that this technology can be developed to suck CO2 out of the air and store it permanently in a solid. "Although we can not literally go back in time, converting carbon dioxide back into coal and burying it in the ground is like rewinding the clock on emissions," Daeneke says. But first, the team's table experience, which Esrafilzadeh calls "a first step," should be replicated on a large scale. In 2017 alone, humans have shed more than 32 billion tonnes of CO2 in the air, according to the International Energy Agency. Converting this amount to solid carbon would essentially replenish the coal mountains miners extract from the soil.

"The magnitude of the gigabytes seems daunting," wrote Douglas MacFarlane, another co-author of the study and chemist at Monash University in Melbourne, in an email. "But if the economic situation becomes encouraging … [then it] seems very possible. "

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