Researchers at the University of Toronto 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. This breakthrough offers a more economically viable method of carbon capture and upgrading, potentially revolutionizing industries such as steel and cement production by allowing them to more efficiently convert CO2 from waste streams.
An electrochemical catalyst for converting CO2 into valuable products can resist an impurity that poisons current versions.
New catalyst improves conversion of captured carbon to commercial products, maintaining high efficiency despite sulfur oxide impurities. This innovation could significantly reduce costs and energy requirements in carbon capture technologies, impacting heavy industry.
A newly designed catalyst created by engineering researchers at the University of Toronto efficiently converts captured carbon into valuable products — even in the presence of a pollutant that impairs the performance of current versions.
The discovery is an important step toward more cost-effective carbon capture and storage techniques that can be added to existing industrial processes.
Advances in Carbon Conversion Technologies
“Today we have more and better options for low-carbon electricity generation than ever before,” says Professor David Sinton (MIE), senior author of a paper published in Natural energy on July 4, which describes the new catalyst.
“But there are other sectors of the economy that will be more difficult to decarbonize: steel and cement production, for example. To help these industries, we need to come up with cost-effective ways to capture and upgrade the carbon in their waste streams.
University of Toronto engineering PhD students Rui Kai (Ray) Miao (left) and Panos Papangelakis (right) hold a new catalyst they designed to convert captured CO2 gas into valuable products. Their version performed well even in the presence of sulfur dioxide, a pollutant that poisons other catalysts. Credit: Tyler Irving / University of Toronto Engineering
Use of electrolyzer in carbon transformation
Sinton and his team use devices known as electrolyzers to convert CO2 and electricity into products such as ethylene and ethanol. These carbon-based molecules can be sold as fuels or used as chemical raw materials to make everyday items like plastics.
Inside the electrolyser, the conversion reaction occurs when three elements – CO2 gas, electrons and a water-based liquid electrolyte – come together 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 minimize the creation of unwanted byproducts, such as hydrogen gas, that reduce the efficiency of the overall process.
Addressing Catalyst Performance Challenges
Although many teams around the world have produced highly efficient catalysts, almost all of them have been designed to work with pure CO2. But if the carbon in question comes from smokestacks, the feed is likely to be anything but clean.
“Catalyst designers generally don’t like to deal with impurities, and for good reason,” said Panos Papgelakis, a PhD student in mechanical engineering and one of five co-authors on the new paper.
“Sulfur oxides, such as SO2, poison the catalyst by binding to the surface. This leaves less room for CO2 to react and also causes the formation of chemicals you don’t want.
“It happens very quickly: while some catalysts can last for hundreds of hours on a clean feed, if you introduce these impurities, within minutes they can drop to 5% efficiency.”
Although there are well-established methods for removing impurities from CO2-rich exhaust gases before they are fed to the electrolyser, they are time-consuming, energy-intensive, and increase the cost of carbon capture and upgrading. Also, in the case of SO2, even a little bit can be a big problem.
“Even if you get your exhaust down to less than 10 parts per million, or 0.001% of the feed, the catalytic converter can still be poisoned in less than 2 hours,” says Papangelakis.
Innovations in catalyst design
In the paper, the team describes how they set about designing a more flexible catalyst that can withstand SO2 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 non-stick material changes the chemistry of the catalyst surface, inhibiting the reactions that allow SO2 poisoning.
On the other side, they added a layer of Nafion, an electrically conductive polymer often used in fuel cells. This complex, porous material contains some areas that are hydrophilic, meaning they attract water, and other areas that are hydrophobic, meaning they repel water. This structure makes it difficult for SO2 to reach the catalyst surface.
Performance in adverse conditions
The team then fed this catalyst a mixture of CO2 and SO2, the latter at a concentration of about 400 parts per million, typical of an industrial waste stream. Even under these difficult conditions, the new catalyst performed well.
“In the paper, we report a Faraday efficiency — a measure of how many of the electrons ended up in the desired products — of 50%, which we were able to maintain for 150 hours,” says Papangelakis.
“There are some catalysts that can start at higher efficiencies, maybe 75% or 80%. But again, if you expose them to SO2, within minutes or a few hours at most, it drops to next to nothing. We were able to withstand that.”
Future directions and implications
Papangelakis says that because his team’s approach does not affect the composition of the catalyst itself, it should be widely applicable. In other words, teams that have already perfected high-performance catalysts should be able to use similar coatings to ensure resistance to sulfur oxide poisoning.
Although sulfur oxides are the most challenging impurities in typical waste streams, they are not the only ones, and the team is targeting the next set of chemical contaminants.
“There are many other impurities to consider, such as nitrogen oxides, oxygen, etc.,” says Papangelakis.
“But the fact that this approach works so well for sulfur oxides is very promising. Prior to this work, it was taken for granted that you had to remove impurities before upgrading CO2. What we’ve shown is that there can be a different way to deal with them, which opens up a lot of new possibilities.”
Reference: “Improving SO2 Tolerance of CO2 Reduction Electrocatalysts Using Polymer/Catalyst/Ionomer Heterojunction Design” by Panagiotis Papangelakis, Rui Kai Miao, Ruihu Lu, Hanqi Liu, Xi Wang, Adnan Ozden, Shijie Liu, Ning Sun, Colin P. O’Brien, Yongfeng Hu, Mohsen Shakouri, Qunfeng Xiao, Mengsha Li, Behrooz Khatir, Jianan Erick Huang, Yakun Wang, Yurou Celine Xiao, Feng Li, Ali Shayesteh Zeraati, Qiang Zhang, Pengyu Liu, Kevin Golovin , Jane Y. Howe , Hongyan Liang, Ziyun Wang, Jun Li, Edward H. Sargent, and David Sinton, 4 Jul 2024, Natural energy.
DOI: 10.1038/s41560-024-01577-9
