Inspired by lightning, eco-friendly reactor converts air and water into ammonia – UBNow: news and opinions for UB faculty and staff

Chances are you owe your existence to the Haber-Bosch process.

This industrial chemical reaction between hydrogen and nitrogen produces ammonia, the key ingredient in synthetic fertilizers that provide much of the world’s food supply and enabled the population explosion of the last century.

It can also threaten the existence of future generations. The process consumes about 2% of the planet’s total energy supply, and the hydrogen needed for the reaction comes primarily from fossil fuels.

Taking inspiration from the way nature, including lightning, produces ammonia, a UB-led team developed a reactor that produces the chemical from nitrogen found in the air and in water, without any carbon footprint.

This plasma-electrochemical reactor, described in a study published in the Journal of the American Chemical Societycan maintain a high ammonia production rate of approximately 1 gram per day for over 1,000 hours at room temperature directly from air.

The researchers say this is a significant step forward toward synthesizing green ammonia at an industrially competitive production rate and reaction stability.

“Ammonia is often considered the chemical that feeds the world, but we also need to realize that the Haber-Bosch process has not been modernized since its invention 100 years ago. It still uses high temperature and high pressure processing and generates a large carbon footprint, making it unsustainable in the long term,” says Chris Li, assistant professor of chemistry in the College of Arts and Sciences and corresponding author of the study. “Our process requires only air and water and can be powered by renewable electricity.”

Nature has its own way of producing fertilizers.

During nitrogen fixation, the electrical energy from a lightning strike breaks apart nitrogen molecules in the atmosphere to form different species of nitrogen oxide. After falling as rainwater, nitrogen oxides are transformed into ammonia by soil bacteria, providing nutrients to plants.

In the UB-led team’s two-stage reactor, the role of lightning is replaced by plasma and the role of bacteria by a copper-palladium catalyst.

“Our plasma reactor converts humidified air into nitrogen oxide fragments, which are then placed in an electrochemical reactor that uses the copper-palladium catalyst to convert them into ammonia,” explains Li.

Importantly, the catalyst is able to adsorb and stabilize the numerous nitrogen dioxide intermediates created by the plasma reactor. The team’s graph theory algorithm identified that most nitrogen oxide compounds must pass through nitric oxide or amine as an intermediate step before becoming ammonia. This allowed the team to cleverly design a catalyst that favorably binds to these two compounds.

“When plasma energy or lightning activates nitrogen, you generate a soup of nitrogen oxide compounds. Simultaneously converting, in our case, up to eight different chemical compounds into ammonia, is incredibly difficult,” notes Xiaoli Ge, first author of the study and a postdoctoral researcher in Li’s lab. “Graph theory essentially allows us to map all the different reaction paths, then identify a bottleneck chemical. We then optimize our electrochemical reactor to stabilize the bottleneck chemical, so that all the different intermediates are selectively converted to ammonia.

Li’s team is currently developing their reactor and is exploring both a start-up and industry partnerships to help bring it to market. The UB Office of Technology Transfer has filed a patent application on the reactor and its methods of use.

More than half of the world’s ammonia is produced by four countries – China, the United States, Russia and India – while many developing countries are unable to produce their own. While the Haber-Bosch process must be carried out on a large scale in a centralized power plant, Li says their system can be carried out on a much smaller scale.

“You can imagine our reactors in something that looks like a medium-sized shipping container with solar panels on the roof. This can then be placed anywhere in the world and generate ammonia on demand for that region,” he says. “This is a very attractive advantage of our system, and it will allow us to produce ammonia for underdeveloped regions with limited access to the Haber-Bosch process.”