Like the shift from fuel-powered cars to electric vehicles, could a move towards electricity-driven reactions enable cleaner manufacturing of valuable chemicals?
Researchers led by Wan Ru Leow, a Principal Scientist at the A*STAR Institute of Sustainability for Chemicals, Energy and Environment (A*STAR ISCE²), are exploring this electrochemical route for nitrile production.
Nitriles contain a carbon-nitrogen (C-N) triple bond, which can be transformed into many other useful chemical groups. This has led to their widespread use as building blocks for pharmaceuticals, dyes and polymers. However, current industrial approaches come with substantial environmental and safety burdens, such as reliance on toxic cyanide reagents, high energy consumption and the release of carbon dioxide and hazardous waste products.
Together with collaborators at the National University of Singapore, Leow and the team developed a less toxic alternative that uses an electrochemical potential, involving the movement of charges, to drive C-N bond formation.
Instead of cyanide, their system uses ammonia as the nitrogen source, which reacts with an aldehyde to form a short-lived intermediate compound. Meanwhile, copper oxide nanorods decorated with clusters of cobalt oxide serve as reaction sites. When the electrochemical potential is applied, the intermediate interacts with the copper sites and loses positively charged hydrogen atoms, whereas cobalt alters the copper oxide’s electron structure to further promote hydrogen removal. Without hydrogen, carbon and nitrogen then form the triple bonds found in nitriles.
“The interplay between the two metal oxide components underpins the high activity and selectivity towards nitrile production. This effectively suppresses waste generation,” said Jiahui Xian, a Scientist at A*STAR ISCE2. Moreover, the reaction is compatible with renewable energy sources and works at room temperature, reducing its energy demands.
The team’s system efficiently converted benzaldehyde to benzonitrile, with 98.7 percent of the electrical charges used in the experiment contributing to the intended reaction. This high Faradaic efficiency was also demonstrated for several other aldehydes and their corresponding nitriles, with efficiencies ranging from 78 to 97 percent.
“In comparison with conventional processes, this electrochemical route represents a fundamentally cleaner, safer and more efficient alternative,” Xian said.
The researchers then explored whether nitrogen oxides, common industrial pollutants, could provide the ammonia required for the process. “Instead of treating nitrogen oxides only as pollutants that need to be removed, we showed they could become a valuable nitrogen feedstock,” Leow said. In a tandem electrochemical system, nitrogen oxides were converted to ammonia at one electrode, while ammonia was consumed to produce benzonitrile at the other.
Building on their laboratory-scale demonstration, the researchers have filed a patent application and envision translating the approach to industrial-scale manufacturing. “Our work establishes a new electrochemical design principle and platform for cyanide-free nitrile production, which can now be further developed through catalyst, reactor and process engineering,” said Leow.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Institute of Sustainability for Chemicals, Energy and Environment (A*STAR ISCE²).
