Researchers experimentally determine reaction mechanism for catalytic ammonia production

Researchers at Stockholm University were able for the first time to study the surface of iron and ruthenium catalysts when ammonia is formed from nitrogen and hydrogen. The study entitled “Operando Probing of the Surface Chemistry During the Haber-Bosch Process” is published in Nature.

Better knowledge of the catalytic process and the possibility of finding even more efficient materials open the door to a green transition in a currently very CO context.₂-intensive chemical industry.

Ammonia, produced using the Haber-Bosch process, is currently one of the most essential commodity chemicals for global fertilizer production, with an annual production of 110 million tons. The newspaper Nature proposed in 2001 that the Haber-Bosch process was the most crucial scientific invention for humanity during the 20th century, as it saved an estimated 4 billion lives by preventing mass starvation. An estimate of the nitrogen content of DNA and proteins in our body shows that half of the atoms can come from Haber-Bosch.

“Despite three Nobel Prizes (1918, 1931 and 2007) for the Haber-Bosch process, it has not been possible to experimentally study the catalyst surface with surface-sensitive methods under real ammonia production conditions ; experimental techniques with surface sensitivity at sufficiently high pressures and temperatures were not feasible,” explains Anders Nilsson, professor of chemical physics at Stockholm University.

“Therefore, different hypotheses about the state of the iron catalyst as metallic or in a nitride, as well as the nature of the intermediate species important for the reaction mechanism, could not be unambiguously verified.”

“What made this study possible is that we built a photoelectron spectroscopy instrument in Stockholm that allows us to study the surfaces of the catalysts under high pressures. Thus, we were able to observe what happens when the reaction occurs directly,” explains David Degerman, postdoc in chemistry. Physics at Stockholm University.

“We have opened a new door in understanding the catalysis of ammonia production with our new instrument, which now allows us to detect reaction intermediates and provide evidence of the reaction mechanism.”

“Locating our Stockholm instrument on one of the world’s brightest X-ray sources at PETRA III in Hamburg was crucial to carrying out the study,” says Patrick Lömker, researcher at Stockholm University. “We can now imagine the future with even brighter sources when the machine upgrades to PETRA IV.”

“We now have the tools to conduct research leading to new catalyst materials for ammonia production that can be better used to combine with hydrogen produced by electrolysis for the green transition of the chemical industry,” says Anders Nilsson.

“It is inspiring to conduct research on a topic so linked to a scientific achievement that has helped humanity immensely. I look forward to continuing the research to find new catalysts that can reduce our dependence on fossil sources. The chemical industry alone represents 8% of global CO₂ emissions,” says Bernadette Davies, a doctoral student in materials chemistry at Stockholm University.

“The long-term prospect of producing ammonia through an electrocatalytic alternative directly powered by solar or wind electricity is most attractive, and we now have tools to scientifically aid this development,” says Sergey Koroidov, researcher at Stockholm University. .

The study was carried out in collaboration with Deutsches Elektronen-Synchrotron (DESY) in Hamburg and Montan University in Austria. The study included former University employees Chris Goodwin, Peter Amann, Mikhail Shiplin, Jette Mathiesen and Gabriel Rodrigez.