Taking cues from how natural processes, including lightning, generate ammonia, a team has invented a reactor that creates this important chemical from atmospheric nitrogen and water, all without emitting carbon.
You might very well owe your life to the Haber-Bosch process.
This major industrial chemical reaction, which combines hydrogen and nitrogen to create ammonia, is essential for producing synthetic fertilizers that feed a large portion of the global population and spurred last century’s population growth.
However, this method could pose risks for future generations. The process accounts for around 2% of global energy consumption, and the hydrogen used mainly derives from fossil fuels.
Inspired by nature’s own ways of producing ammonia—such as through lightning—a research team from the University at Buffalo has engineered a reactor that synthesizes ammonia using nitrogen from the air and water, while leaving no carbon footprint.
Described in a paper published in the Journal of the American Chemical Society, this plasma-electrochemical reactor can maintain a high production of ammonia at about 1 gram daily for over 1,000 hours at room temperature, directly from the air.
The researchers claim this represents a major leap towards sustainable ammonia production that can compete on an industrial scale while ensuring consistent reactions.
“Ammonia is often seen as the chemical that nourishes the world, yet we must acknowledge that the Haber-Bosch method has remained unchanged for the past century. It still requires extreme temperatures and pressures, resulting in significant carbon emissions, which is not viable for the future,” states Chris Li, PhD, the study’s lead author and an assistant professor of chemistry in the UB College of Arts and Sciences. “Our method only necessitates air and water and can be powered by renewable electricity.”
Imitating nature’s nitrogen cycle
Nature has its own effective means of creating fertilizer.
During nitrogen fixation, lightning’s electrical energy splits nitrogen molecules in the atmosphere, forming various nitrogen oxides. When these oxides precipitate as rainwater, bacteria in the soil convert them to ammonia, providing vital nutrients to plants.
In the reactor devised by the UB-led team, plasma takes on the role of lightning, and a copper-palladium catalyst stands in for bacteria.
“Our plasma reactor turns humidified air into fragments of nitrogen oxide, which then enter an electrochemical reactor where the copper-palladium catalyst transforms them into ammonia,” explains Li.
Notably, the catalyst can absorb and stabilize many nitrogen dioxide intermediates generated by the plasma reactor. Through graph theory, the researchers determined that most nitrogen oxide compounds need to transition through nitric oxide or amines before becoming ammonia. This insight enabled the design of a catalyst that effectively bonds with these compounds.
“When plasma or a lightning strike activates nitrogen, it produces a complex mixture of nitrogen oxide compounds. Converting as many as eight different chemicals into ammonia simultaneously poses a significant challenge,” says Xiaoli Ge, the primary author of the study and a postdoctoral researcher in Li’s lab. “Graph theory helps us chart all possible reaction pathways and pinpoint a critical limiting factor. We then optimize our electrochemical reactor to support this limiting compound, facilitating the selective conversion of all intermediate compounds into ammonia.”
Scaling up
Li’s team is now working to scale up their reactor and is considering partnerships with industries to aid commercialization. The UB Technology Transfer Office has filed for a patent on the reactor and its operational methods.
More than half of the world’s ammonia is manufactured by just four nations—China, the United States, Russia, and India—leaving many developing countries unable to produce their own. While the Haber-Bosch method requires large-scale operations in centralized plants, Li points out that their approach can be implemented on a much smaller scale.
“Picture our reactors housed within a medium-sized shipping container topped with solar panels. These can be deployed anywhere globally to generate ammonia on demand for local needs,” he shares. “This offers an exciting advantage and could supply ammonia to underdeveloped regions with restricted access to the Haber-Bosch method.”
