University of Michigan Chemist Charles McCrory and his research group, along with Jesús Velázquez‘s lab at the University of California, Davis and Anastassia Alexandrova‘s lab at the University of California, Los Angeles, have developed a method to capture carbon dioxide and turn it into metal oxalates, which then can be used as precursors for cement production.
“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.
“We’re not just taking carbon dioxide and burying it; we’re taking it from different point sources and repurposing it for something useful.”
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 and carbon footprint, McCrory said.
McCrory and colleagues were looking into ways to take carbon dioxide and convert it into materials that can be used for the production of alternative cement.
One type of material that can be used as an alternative cement precursor is metal oxalates, simple salts.
Researchers know that lead can be used as a catalyst – a substance that helps facilitate a chemical reaction – that can convert carbon dioxide into metal oxalates.
However, the process requires large amounts of lead catalysts, which is an environmental and human health hazard.
The team was able to use 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.
The researchers showed that by controlling the microenvironment surrounding the lead catalyst in the chemical reaction that converts carbon dioxide to oxalate, they can vastly reduce the amount of lead needed for the process.
To produce the oxalate from carbon dioxide, the researchers use a set of electrodes. At one electrode, carbon dioxide is converted to oxalate, which is an ion dissolved in the solution.
The other electrode is a metal electrode that’s being oxidised and releasing metal ions that bind with the oxalate ion and precipitate 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.”
“Metal oxalates represent an underexplored frontier – serving as alternative cementitious materials, synthesis precursors and even carbon dioxide storage solutions,” said Velázquez, co-lead author of the study and Associate Professor of chemistry at UCD.
“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, co-lead author of the study and Professor of chemistry and materials science at UCLA.
“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.”
McCrory says once the carbon dioxide is converted into the metal oxalate solid, it won’t be rereleased into the atmosphere as carbon dioxide again under normal conditions.
“It’s a true capture process because you’re making a solid from it,” he said.
“But it’s also a useful capture process because you’re making a useful and valuable material that has downstream applications.”
McCrory says researchers should be able to scale up one part of the process: researchers are working on electrolysis for carbon dioxide on a large scale.
The next step will be to study how to scale up the portion of the process that produces the solid product.
“We are a way 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.”