MIT Finds a Faster Way to Search for Greener Ammonia Catalysts

MIT researchers have developed a way to predict which materials could work best as catalysts for producing ammonia electrochemically, a low-emissions alternative to the century-old Haber-Bosch process that currently makes the vast majority of the world's ammonia. The findings were published August 11 in the Royal Society of Chemistry journal EES Catalysis.

Ammonia, used mainly to make fertilizer, is the second-most-produced chemical in the world after sulfuric acid, but making it accounts for up to 2% of global energy consumption and about 1.5% of greenhouse gas emissions. The traditional Haber-Bosch process relies on fossil fuels for both heat and the hydrogen it needs. An electrochemical alternative exists but has not been economically competitive at industrial scale, partly because production rates and yields with existing catalysts are too low.

Rather than testing millions of possible alloy combinations by trial and error, the MIT team used a computational method called density functional theory, which applies quantum mechanics to simulate how atoms in a material behave, to identify the physical properties that make a catalyst effective at the reaction. The researchers focused on transition metal nitride compounds and found electronic properties, based on how electrons are shared between nitrogen and metal atoms, that predict how well a material drives the reaction that turns nitrogen gas into ammonia.

"Our approach identifies the key physical properties that drive catalytic activity in ammonia production," said Bilge Yildiz, a professor in MIT's departments of Nuclear Science and Engineering and Materials Science and Engineering, who led the study with doctoral students Constantine Athanitis and Filip Grajkowski. The world currently uses about 200 million metric tons of ammonia a year, and more than 90% of it still comes from the Haber-Bosch process, according to the researchers.