Unstoppable catalyst beats sulfur to revolutionize carbon capture

Researchers at the University of Toronto’s Department of Engineering have developed a new catalyst that efficiently converts captured carbon into valuable products such as ethylene and ethanol, even in the presence of sulfur oxide pollutants. The discovery offers a more economically viable way to capture and enhance carbon, potentially revolutionizing industries such as steel and cement manufacturing by allowing them to divert carbon dioxide from waste streams more effectively.

An electrochemical catalyst for converting carbon dioxide into valuable products could combat the impurities that poison current versions.

A new catalyst boosts the conversion of captured carbon into commercial products, while maintaining high efficiency despite sulfur oxide impurities. The innovation could dramatically reduce costs and energy requirements in carbon capture technologies, impacting heavy industries.

Researchers at the University of Toronto’s Department of Engineering have created a new catalyst that efficiently converts captured carbon into valuable products — even in the presence of a contaminant that degrades the performance of existing versions.

This discovery is an important step towards more economically viable carbon capture and storage technologies that can be added to existing industrial processes.

Developments in carbon conversion technologies

Professor David Sinton (MIE), lead author of a research paper published in the journal, says: Energy of nature On July 4th describing the new catalyst.

“But there are other sectors of the economy that will be difficult to decarbonise: steel and cement manufacturing, for example. To help these industries, we need to come up with cost-effective ways to capture and upscale carbon in waste streams.”

University of Toronto engineering doctoral students Roy Kai (Ray) Miao (left) and Panos Papangelakis (right) hold up a new catalyst they designed to convert captured carbon dioxide into valuable products. Their model works well even in the presence of sulfur dioxide, a pollutant that poisons other catalysts. Image credit: Tyler Irving/University of Toronto Engineering

Use of electrolyzer in carbon conversion

Sinton and his team use devices known as electrolyzers to convert carbon dioxide and electricity into products like ethylene and ethanol. These carbon-based molecules can be sold as fuel or used as chemical raw materials to make everyday items like plastics.

Inside the electrolyzer, a conversion reaction occurs when three elements—carbon dioxide gas, electrons, and a water-based liquid electrolyte—combine on the surface of a solid catalyst.

The catalyst is often made of copper but may also contain other metals or organic compounds that can further improve the system. Its function is to speed up the reaction and reduce the formation of unwanted side products, such as hydrogen gas, which reduces the overall process efficiency.

Addressing catalyst efficiency challenges

While many research teams around the world have succeeded in producing high-performance catalysts, almost all of them are designed to operate on pure CO2. But if the carbon in question comes from a smokestack, the resulting carbon is likely to be far from pure.

“Catalyst designers generally don’t like dealing with impurities, and for good reason,” says Panos Papangelakis, a doctoral student in mechanical engineering and one of five co-authors on the new paper.

“Sulfur oxides, such as sulfur dioxide, poison the catalyst by binding to the surface. This leaves fewer sites for the carbon dioxide to react, and also causes chemicals to form that you don’t want.

“It happens very quickly: while some catalysts can last hundreds of hours on pure feed, if you introduce these impurities, their efficiency can drop to 5% within minutes.”

Although there are well-established methods for removing impurities from CO2-rich exhaust gases before they enter the electrolyzer, these methods are time-consuming, energy-intensive, and costly for carbon capture and upgrading. Moreover, in the case of SO2, even a little bit can be a big problem.

“Even if you reduce the exhaust gas to less than 10 parts per million, or 0.001 percent of the feed, the catalyst can still be poisoned in less than two hours,” says Papangelakis.

Innovations in catalyst design

In this paper, the team describes how they designed a more flexible catalyst that can resist sulfur dioxide by making two key changes to a typical copper-based catalyst.

On one side, they added a thin layer of polytetrafluoroethylene, also known as Teflon. This nonstick material changes the chemistry on the catalyst’s surface, hindering the reactions that enable sulfur dioxide poisoning to occur.

On the other side, they added a layer of Nafion, an electrically conductive polymer commonly used in fuel cells. This complex, porous material has some regions that are hydrophilic, meaning they attract water, and others that are hydrophobic, meaning they repel it. This structure makes it difficult for sulfur dioxide to reach the surface of the catalyst.

Performance under adverse conditions

The team then fed this catalyst a mixture of carbon dioxide and sulfur dioxide, the latter at a concentration of about 400 parts per million, which is typical of industrial waste streams. Even under these challenging conditions, the new catalyst performed well.

“In this study, we reported a Faraday efficiency — a measure of how many electrons ended up in the desired products — of 50 percent, which we were able to maintain for 150 hours,” says Papangelakis.

“There are some catalysts that might start out at a higher efficiency, maybe 75% or 80%. But again, if you get exposed to sulfur dioxide, within minutes or at most a few hours, that efficiency drops to almost zero. We’ve been able to resist that.”

Future trends and implications

Papangelakis says his team’s approach doesn’t affect the composition of the catalyst itself, so it should be widely applicable. In other words, teams that have already perfected high-performance catalysts should be able to use similar coatings to make them resistant to sulfur oxide poisoning.

Although sulfur oxides are the most challenging impurities in typical waste streams, they are not the only ones, as the team then turns to the full range of chemical pollutants.

“There are a lot of other impurities to consider, like nitrogen oxides, oxygen, etc,” says Papangelakis.

“But the fact that this approach works so well with sulfur oxides is very promising. Before this work, it was taken for granted that you had to remove the impurities before you could upgrade the carbon dioxide. What we have shown is that there may be a different way to deal with them, which opens up a lot of new possibilities.”

Reference: “Improving SO2 Tolerance of Electrocatalysts for CO2 Reduction Using Polymer/Catalyst/Ionomer Heterojunction Design” by Panagiotis Papangelakis, Rui Kai Miao, Ruihu Lu, Hanqi Liu, Shi Wang, Adnan Ozden, Shiji Liu, Ning Sun, Colin P. O’Brien, Yongfeng Hu, Mohsen Shakouri, Qunfeng Xiao, Mingsha Li, Behrouz Khatir, Jiannan Eric Huang, Yaqun Wang, Yuro Celine Xiao, Feng Li, Ali Shayesteh Zarati, Qiang Zhang, Bingyu Liu, Kevin Golovin, Jin Wei Hao, Hongyan Liang, Zhiyun Wang, Jun Li, Edward H. Sargent, David Sinton, July 4, 2024, Energy of nature.
DOI: 10.1038/s41560-024-01577-9