With boron, nitrogen can be converted into ammonium. Photo credit: Team Braunschweig
Mankind depends on the ammonium in synthetic fertilizers for food. However, the production of ammonia from nitrogen is extremely energy-intensive and requires the use of transition metals.
Researchers at the Julius Maximilians University (JMU) Würzburg in Bavaria have now achieved the conversion of nitrogen into ammonium at room temperature and low pressure without transition metals. This is what a research group led by JMU scientist Holger Braunschweig reported in the journal Natural chemistry.
A new toolbox for fixing nitrogen
The industrial production of ammonia, the so-called Haber-Bosch process, requires high temperatures and pressures and uses an estimated two percent of all energy produced on earth. This process is also based on transition metal elements, relatively heavy and reactive atoms.
In 2018, Professor Braunschweig’s team reported on the binding and chemical conversion of nitrogen using a molecule that consists only of lighter non-metal atoms. A year later, they used a similar system to demonstrate the first combination of two nitrogen molecules in the laboratory, a reaction otherwise only observed in the upper atmosphere and below plasma Conditions.
The key to these two discoveries was the use of boron, the fifth lightest element, as a atom to which the nitrogen binds. “After these two discoveries, it was clear that we had a very special system in our hands,” says Braunschweig.
Just add water
Even though their system fixes and converts nitrogen, only half of the puzzle pieces were in place. “We knew that converting nitrogen into ammonia would be a major challenge, as a complex sequence of chemical reactions is required that are often incompatible with one another,” explains the JMU professor.
The breakthrough came with the simplest of reagents: traces of water left in a sample were enough to fuel a sequential reaction that took the team just one step away from the target ammonium. It was later discovered that the key reactions could be carried out using a solid acidThis allows the reactions to take place sequentially in a single reaction flask at room temperature.
Making ammonium with beer
When the team realized that the acidification step of the process seemed to work even with simple reagents such as water, they repeated the reaction with locally brewed Würzburger Hofbräu beer. To their delight, they were able to detect the pre-ammonium product in the reaction mixture.
“This experiment was a bit fun at times, but it also shows how tolerant the system is towards water and other compounds,” explains Dr. Marc-André Légaré, the postdoctoral fellow who initiated the study. “The reduction of nitrogen to ammonia is one of the most important chemical reactions for mankind. This is hands down the first time beer has been used, and it is particularly fitting that it was made in Germany! “Says Dr. Rian Dewhurst, Senior Academic Councilor and co-author of the study.
Much remains to be done
The reaction, while exciting, is far from being a practical process for the industrial production of ammonium. Ideally, a way needs to be found to reshape the active species in order to make the process energy efficient and economical.
Even so, the discovery is an exciting demonstration that the lighter elements can overcome even the greatest challenges in chemistry. “There is still a lot to do here, but Bor and the other lighting elements have surprised us so often. They can clearly do a lot more, ”says Holger Braunschweig.
Reference: “One-pot conversion of dinitrogen to ammonium chloride at room temperature on a main group element” by Marc-André Légaré, Guillaume Bélanger-Chabot, Maximilian Rang, Rian D. Dewhurst, Ivo Krummenacher, Rüdiger Bertermann and Holger Braunschweig, September 14, 2020, Natural chemistry.
DOI: 10.1038 / s41557-020-0520-6
