University of California researchers, in collaboration with University of Michigan researchers, have developed a method to take carbon dioxide, an industrial waste product that pollutes the atmosphere, and turn it into something useful: precursors to make cement.

The study, published in Advanced Energy Materials, is based on research that originated in the lab of Jesús Velázquez, of the University of California, Davis. The research team also consisted of University of Michigan’s Charles McCrory’s lab, and University of California, Los Angeles’ Annastassia Alexandrova’s lab. The team developed a methodology for capturing carbon dioxide and converting it into metal oxalates. These oxalates may subsequently act as precursors for cement production.

“Our research lays the groundwork for the future application of captured carbon dioxide from dilute streams in the manufacture of valuable construction materials,” said Velázquez, an associate professor in the Department of Chemistry at the College of Letters and Science at UC Davis. “This approach has the potential to reduce costs associated with carbon capture and conversion while simultaneously transforming the manufacturing processes of essential industrial products, such as steel and concrete.”

The study was supported by the research team’s participation in the Center for Closing the Carbon Cycle (4C). 4C is an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, and is led by Jenny Yang at University of California, Irvine. One of the goals of 4C is to explore methods for capturing and converting carbon dioxide into valuable fuels and products.

"This research shows how we can take carbon dioxide, which everyone knows is a waste product that is of little-to-zero value, and upcycle it into something that's valuable," said McCrory, associate professor of chemistry and macromolecular science and engineering.

Rethinking cement production

The most common type of cement is Portland cement, which is typically made from limestone and minerals such as calcium silicates. Producing this Portland cement has a relatively large energy cost, McCrory said.

The researchers were looking into ways to take carbon dioxide and convert it into materials that can be used for production of alternative cements. One type of material that can be used as an alternative cement precursor are metal oxalates, simple salts.

“Metal oxalates offer a unique opportunity to link carbon dioxide conversion with material production,” said Rowan Brower, the first author of the study and a graduate student in the Velázquez Lab. “These compounds are not only relatively simple to synthesize under mild conditions, but they serve as a precursor to functional metal oxides.”

Historically, researchers have known that lead can be used as a catalyst — a substance that helps facilitate a chemical reaction — for converting carbon dioxide into metal oxalates. But the process requires large amounts of lead catalysts, which is an environmental and human health hazard.

The 4C team used polymers to control the environment immediately surrounding the lead catalysts, shaving the amount of lead needed in this process down to parts per billion — a trace impurity level of lead found in many commercial porous graphite and carbon materials.

By controlling the microenvironment surrounding the lead catalyst in the chemical reaction that converts carbon dioxide to oxalate, the researchers vastly reduced the amount of lead needed for the process.

Finding the right synthesis

To produce the oxalate from carbon dioxide, the researchers used a set of electrodes. At one electrode, carbon dioxide was converted to oxalate. The other electrode was a metal electrode that was oxidized and released metal ions that bind with the oxalate ion, precipitating it out of solution as a metal oxalate solid.

"Those metal ions are combining with the oxalate to make a solid, and that solid crashes out of the solution," McCrory said. "That's the product that we collect and that can be mixed in as part of the cement-making process."

Velázquez and his group originated the idea of using trace amounts of lead to drive the oxalate-synthesis reactions and examined the mechanisms behind the chemical reaction of carbon dioxide into oxalate.

"Metal oxalates represent an underexplored frontier — serving as alternative cementitious materials, synthesis precursors, and even carbon dioxide storage solutions," Velázquez said.

Velázquez credited Brower for commencing the foundational science underlying the study and identifying the catalyst and reaction environment that made the research a success. 

“Due to her meticulous attention to detail, she was able to identify that trace metal impurities, such as lead, are present in the carbon electrode supports that we purchase,” Velázquez said. “Subsequently, she recognized that by incorporating a polymer overlayer, we can enhance the promoting activity of the trace lead/carbon support within the substrates as received from the manufacturer.”

“I began developing this concept during my early years in graduate school, and it’s been incredibly meaningful to see it evolve into a full platform for reactive carbon dioxide conversion and long-term storage,” added Brower, who after graduating will be moving into a managing editor position with ACS Publications. “The result is a more efficient and scalable system that turns a common material impurity into a functional design feature.”

A true capture process

Anastassia Alexandrova, also a co-lead author of the study and a professor of chemistry and materials science at UCLA, and her team performed calculations to confirm the hypothesis that this mechanism would work.

"Catalysts are often discovered by accident, and successful industrial formulations are often very complicated. These cocktail catalysts are discovered empirically through trial and error," Alexandrova said. "In this work, we have an example of a trace lead impurity actually being a catalyst. I believe there are many more such examples in practice catalysis, and also that this is an underexplored opportunity for catalyst discovery."

Brower said that since metal oxalates don’t readily release carbon dioxide back into the environment under ambient conditions, they’re well-suited for long-term storage.

"It's a true capture process because you're making a solid from it," McCrory added. "But it's also a useful capture process because you're making a useful and valuable material that has downstream applications."

The next steps will be to further study how to scale up the portion of the process that produces the solid product.

"We are a ways away, but I think it's a scalable process," McCrory said. "Part of the reason we wanted to reduce the lead catalyst to parts per billion is the challenges of scaling up a catalyst with massive amounts of lead. It wouldn’t be environmentally reasonable, otherwise."

This article is adapted from a University of Michigan press release.

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