New catalyst helps capture carbon from smokestacks

University of Toronto Engineering Ph.D. students Rui Kai (Ray) Miao (left) and Panos Papangelakis (right) hold up a new catalyst they designed to convert captured CO2 gas into valuable products. Credit: Tyler Irving / University of Toronto.

Researchers at the University of Toronto have developed a new catalyst that can efficiently convert captured carbon into valuable products, even in the presence of contaminants that usually degrade current versions.

This breakthrough could make carbon capture and storage more economically viable, especially for industries like steel and cement manufacturing, which are hard to decarbonize.

Professor David Sinton, the senior author of the study published in Nature Energy, explained the importance of this development.

“Today, we have more and better options for low-carbon electricity generation than ever before. But there are other sectors of the economy that will be harder to decarbonize.

To help those industries, we need to invent cost-effective ways to capture and upgrade the carbon in their waste streams.”

Sinton’s team uses devices called electrolyzers to convert CO2 and electricity into products like ethylene and ethanol.

These products can be used as fuels or as raw materials for making everyday items such as plastic.

The conversion happens inside the electrolyzer when CO2 gas, electrons, and a water-based liquid electrolyte come together on the surface of a solid catalyst.

While many researchers have created high-performing catalysts, they typically require a pure CO2 feed. However, CO2 from smokestacks often contains impurities that can “poison” the catalyst, reducing its efficiency.

“Catalyst designers generally don’t like dealing with impurities, and for good reason,” said Panos Papangelakis, a Ph.D. student and one of the lead authors of the study. “Sulfur oxides, such as SO2, poison the catalyst by binding to the surface.

This leaves fewer sites for CO2 to react and causes the formation of unwanted chemicals.”

The presence of SO2 can quickly reduce a catalyst’s efficiency from hundreds of hours to just a few minutes. Although there are methods to remove impurities from CO2-rich exhaust gases, they require time, energy, and increase costs. Even a small amount of SO2 can be problematic, poisoning the catalyst in under two hours even at low concentrations.

To overcome this challenge, the team made two key changes to a typical copper-based catalyst. They added a thin layer of polytetrafluoroethylene (Teflon) on one side and a layer of Nafion, an electrically-conductive polymer, on the other. Teflon changes the surface chemistry of the catalyst, preventing SO2 poisoning, while Nafion’s complex structure makes it hard for SO2 to reach the catalyst surface.

Testing the new catalyst with a mix of CO2 and SO2 at typical industrial concentrations showed promising results. The catalyst maintained a Faraday efficiency—a measure of how many electrons ended up in the desired products—of 50% for 150 hours. While other catalysts might start at higher efficiencies, they quickly degrade in the presence of SO2.

Papangelakis noted that this approach doesn’t change the catalyst’s composition, meaning other high-performing catalysts could use similar coatings to resist sulfur oxide poisoning. Although sulfur oxides are the most challenging impurities, they are not the only ones. The team plans to tackle other contaminants next.

“There are lots of other impurities to consider, such as nitrogen oxides and oxygen,” Papangelakis said. “But the fact that this approach works so well for sulfur oxides is very promising. Before this work, it was just taken for granted that you’d have to remove the impurities before upgrading CO2. What we’ve shown is that there might be a different way to deal with them, which opens up a lot of new possibilities.”

This discovery could significantly advance carbon capture technology, making it more practical and cost-effective for heavy industries to reduce their carbon emissions and help combat climate change.