Fertilizers are essential for feeding the world. But making ammonia, the key ingredient of fertilizers, produces large amounts of carbon dioxide emissions.
Chemists have now made a device that produces ammonia by drawing water vapor and nitrogen from air. The device, reported in the journal Science Advances, could dramatically cut down the carbon emissions of ammonia production.
Ammonia is the second most-produced chemical in the world. About 180 million metric tons of ammonia is produced every year. Most all of it is made using the Haber–Bosch process, which reacts hydrogen and atmospheric nitrogen at high pressures and temperatures. The hydrogen typically comes from natural gas. The process results in 2.4 metric tons of carbon dioxide for every ton of ammonia produced, amounting to 2% of annual carbon dioxide emissions.
Researchers have been trying to come up with alternative, low-energy routes to making ammonia. There are efforts to use renewable energy to split water to obtain the hydrogen. Others are looking at innovative ways, such as the use of lasers, to break the strong bonds in nitrogen to make it more reactive with hydrogen.
In the new work, researchers at Stanford University and King Fahd University of Petroleum and Minerals in Saudi Arabia coated copper mesh with iron oxide and a polymer to make a special catalyst mesh. When they pass air through the mesh, it condenses water vapor into small droplets, which react with nitrogen to give ammonia.
The researchers optimizes this ammonia production and scaled up the process in the laboratory. They analyzed how environmental factors such as humidity, wind speed, salt levels, and acidity affect ammonia production. The team also evaluated how factors such as water droplet size and the contact of water with the mesh impacted the process.
Using this information, they made a prototype device that could produce ammonia onsite in the outside world. A suction pump draws ambient air into the device, exposing the catalytic mesh surface to nitrogen and water vapor. The ammonia-rich solution is collected by a condenser plate, separating it from the air and water vapor in the chamber.
The portable device could lead to localized, sustainable green ammonia production, the team writes in the paper. When developed, it “would reduce the reliance on large-scale industrial facilities and the associated transportation costs and emissions, contributing to a more sustainable agricultural ecosystem.”
Source: Xiaowei Song et al. Onsite ammonia synthesis from water vapor and nitrogen in the air. Sci. Adv. 2024.
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