CO2 and the cyclic economy

University of Toronto doctoral student Phil De Luna has always liked the idea of carbon sequestration, but he acknowledges that it needs some help. After all, he suggests, there must be better things to do with captured CO₂ – ideally more sustainable things – than simply hope to keep it underground and out of the atmosphere. Any technology that could turn this notorious greenhouse gas into a useful product would play a key role in a cyclic economy, where waste products become valuable resources.

Thanks to an innovative experiment at the Canadian Light Source (CLS) in Saskatoon, De Luna and his colleagues in Professor Ted Sargent’s diverse and dynamic research group have demonstrated how to do just that: turn CO₂ into ethylene, a widely used chemical feedstock for plastic production. The result, which was published in the newly launched journal Nature Catalysis, offers not just a new perspective on sequestration, but the prospect of recycling the world’s growing mounds of post-consumer plastic waste.

This accomplishment has also earned the researchers a place as semi-finalists in the Carbon Xprize, a $20 million international competition sponsored by US energy giant NRG and Canada’s Oil Sands Innovation Alliance (COSIA), a research collaboration of 13 Canadian companies in that field. The Sargent Group turned to Xerox Research Centre of Canada (XRCC) to build and operate a micropilot unit at their facility in Mississauga, Ontario, where they have been advancing the technology towards scale-up to commercial operation.

This achievement began with the possibility of using electrocatalysis and electrolytes to make CO₂ and convert it to ethylene in the presence of a solid catalyst. De Luna identified a copper-containing catalyst as the best for the job.

“Copper is a really special metal,” De Luna explains. “It can take carbon dioxide and convert it to higher, more valuable, hydrocarbon goods.”

The surface of a nanostructured copper catalyst that converts CO₂ into ethylene. Photo credit: Phil De Luna

The easy part, he adds, is getting copper to generate various products from CO₂. The real trick is getting it to produce just one — ethylene — rather than a distribution of hydrocarbons that introduce the additional challenges of isolation and separation. De Luna teamed up with fellow doctoral student Rafael Quintero-Bermudez, who framed an experimental approach for determining how the shape of the catalyst affected its activity. By bombarding a sample with high powered x-rays as the catalyst was active in an electrolyte under relevant process conditions, they were able to identify a configuration that would result in selective ethylene production.

“This kind of experiment had never been done before ­— doing it in real time under real operating conditions in a liquid electrolyte flow cell,” says De Luna, who credits CLS senior scientist Tom Regier with constructing a unique piece of equipment that allowed this cell to function in the ultra-high vacuum setting necessary to generate the right data. Innovative thinking and design of this evacuated chamber, about one millimeter in height with windows to allow the synchrotron beam to pass, made it possible to collect the necessary fluorescence yield mode measurements.

“We were able to study for the first time the copper oxidation state during the reaction,” observes De Luna. “We were able to establish the conditions to make our catalyst very selective.”

By scaling up those conditions to industrial relevant levels, sequestration turns from an exercise in hiding an unwanted by-product to harnessing a valuable resource. Nor has De Luna forgotten about what ultimately happens to the plastic that would be made from this resource.

“You can burn it,” he suggests. “By capturing the CO₂ that you generate that way, you can turn it into ethylene and make more plastic, which closes the cycle”.