Few people have heard of the chemical ethylene oxide, but all of us have used products that rely on it for their production, from antifreeze and plastics to textiles and disinfectants. It’s a “platform chemical”—the basis for many other chemicals—and there’s a $40 billion annual worldwide market for it.

The ethylene oxide production process emits millions of tons of CO₂ into the atmosphere, which contributes to climate change. The process also currently requires chlorine, which is toxic. Now a team of researchers led by Tufts chemistry professor Charles Sykes has discovered an inexpensive way to potentially reduce CO₂ emissions and decrease the need for chlorine to produce the chemical. 

Writing in the journal Science, the researchers describe how adding small amounts of nickel atoms to silver catalysts made the reaction just as efficient, but without the need for chlorine that is currently used. This could revolutionize the production of the ubiquitous chemical ethylene oxide.

It was a long road to the discovery. Sykes, who is John Wade Professor of Chemistry, first discussed the idea with collaborator Matthew Montemore, a chemical engineering professor at Tulane University, six years ago. They were interested in exploring selective oxidation reactions, and settled on ethylene oxide production, which is made from ethylene and molecular oxygen. 

Catalysts break the strong O₂ bond, allowing single atoms of oxygen to bind with the ethylene to form ethylene oxide. (Catalysts are substances that increase the rate of a chemical reaction without undergoing chemical change themselves.) Silver is the main catalyst for making ethylene oxide, but it produces two molecules of CO₂ for every molecule of ethylene oxide; adding chlorine brings it to about one molecule of CO₂ per two ethylene oxide molecules produced, but there was still room for improvement. 

Knowing the safety and environmental impacts of current industrial production methods that rely on chlorine, Sykes and Montemore looked for elements they could add to the silver catalyst to substitute for chlorine. “The answer was nickel,” Sykes says “which surprised us because we couldn’t find anything in the scientific or patent literature about nickel despite it being a common and inexpensive element used in many other catalytic processes. Could 70+ years of industrial R&D have missed it?” 

Testing the Prediction

In his lab at Tufts, Sykes worked with graduate students Elizabeth Happel, AG25, and Laura Cramer, AG21, to do the fundamental experiments “to test Matthew Montemore’s prediction and see how far it could go towards application,” he says. The results were promising.

They used Sykes’ single-atom alloy concept—a fundamental approach to understanding and controlling chemical reactions that he had pioneered over a decade earlier. By adding nickel in the form of individual atoms to silver, they were able to carefully test how it would work as a catalyst. “It was fundamental research, but our results indicated that it may be applicable to real industrial catalysts,” Sykes says.

He enlisted Phillip Christopher, a professor of chemical engineering at the University of California Santa Barbara (UCSB), to make a new formulation of the silver catalyst by adding tiny amounts of nickel, to see how it might work. “Selective oxidation is one of the more challenging reactions, and so I wouldn’t have been surprised if it hadn’t have worked,” says Sykes. But it did. 

“Incorporating nickel atoms into the silver catalyst by a reproducible protocol was a real technical hurdle that Anika Jalil, a Ph.D. student at UCSB, navigated impressively. The challenge in incorporating nickel could be why the effect we observed was never previously reported,” Christopher says.

Because nickel added to the catalyst improves the efficiency of the process, it might now be possible to lower the amount of CO₂ that is released in the making of ethylene oxide. “I have worked on ethylene oxide catalysts since my PhD and was so surprised and excited by the magnitude of the effect nickel addition had,” Christopher says.

The team submitted a provisional patent in 2022 and an international patent in 2023. They are also in regular contact with a major commercial producer of ethylene oxide, interested in seeing if their discovery can be implemented in existing manufacturing facilities.