Eco-friendly reactor mimics lightning to produce ammonia from air and water

There’s a good chance you owe your existence to the Haber-Bosch process.

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

It may also threaten the existence of future generations. This process consumes about 2% of the world’s total energy supply, and most of the hydrogen needed for the reaction comes from fossil fuels.

Inspired by how lightning and other natural phenomena produce ammonia, a team led by the University at Buffalo has developed a reactor that produces chemicals from nitrogen in the air and water, without any carbon emissions. .

The plasma electrochemical reactor, described in a study published in the Journal of the American Chemical Society, can maintain high ammonia production rates of about 1 gram per day for more than 1,000 hours at room temperature, converting air into Generate directly.

The researchers say this is a major advance towards green ammonia synthesis with industrially competitive production rates and reaction stability.

“Although we often think of ammonia as the chemical that feeds the world, we also have to face the reality that the Haber-Bosch process has not been modernized since its invention 100 years ago. “High-temperature, high-pressure processing is still used today, has a large carbon footprint, and is unsustainable in the long term,” said Chris Lee, Ph.D., corresponding author of the study and assistant professor of chemistry in the UB College of Arts and Sciences. I am. “Our process requires only air and water and can be powered by renewable electricity.”

Mimics the natural nitrogen cycle

Nature has its own way of producing fertilizer.

In nitrogen fixation, the electrical energy of a lightning strike destroys nitrogen molecules in the atmosphere, forming various nitrogen oxide species. After nitrogen oxide falls as rainwater, it is converted by bacteria in the soil to ammonia, which provides nutrients to plants.

The UB-led team’s two-stage reactor replaces the role of lightning with plasma and the role of bacteria with a copper-palladium catalyst.

“Our plasma reactor is placed in an electrochemical reactor that converts humidified air into nitrogen oxide fragments, which are then converted to ammonia using a copper-palladium catalyst,” says Lee.

Importantly, the catalyst can adsorb and stabilize a large number of nitrogen dioxide intermediates produced by the plasma reactor. The researchers’ graph theory algorithm determined that most nitrogen oxide compounds need to cycle through nitric oxide or amines as an intermediate step before becoming ammonia. This allowed the team to intelligently design a catalyst that binds well to these two compounds.

“When nitrogen is activated by plasma energy or lightning, it creates a soup of nitrogen oxide compounds. In our case, converting up to eight different compounds to ammonia at the same time is incredibly difficult.” said Xiaoli Ge, lead author of the study. Postdoctoral researcher in Lee’s lab. “Graph theory basically allows you to plan out all the different reaction paths and identify the bottleneck chemicals. Then you can optimize the electrochemical reactor to stabilize the bottleneck chemicals, It ensures that all the various intermediates are selectively converted to ammonia.”

scale up

Lee’s team is currently scaling up the reactor and is exploring both startup and industry partnerships to support commercialization. UB’s Technology Transfer Office has applied for a patent for the reactor and its method of use.

More than half of the world’s ammonia is produced in four countries: China, the United States, Russia, and India, but many developing countries cannot produce their own ammonia. Unlike the Haber-Bosch process, which must be implemented on a large scale in centralized power plants, Lee says his system can be implemented on a much smaller scale.

“Imagine our nuclear reactor is housed in something like a medium-sized shipping container with solar panels on the roof. We can set this up anywhere in the world, and we can adapt it depending on local demand. It can produce ammonia,” he says. “This is a very attractive advantage of our system, which allows us to produce ammonia even in undeveloped areas with limited access to the Haber-Bosch process.”