A combined experimental and computational study shows promising results for a new class of catalysts producing ammonia under mild conditions.

There are several means of producing ammonia, but the Haber-Bosch process remains the most prevalent, accounting for about 90 % of total production. In any case, Haber-Bosch and the other processes involved in industrial-scale production require high temperatures (more than 400°C) and high pressure (more than 150 bar). Those conditions are needed to break the strong bonds in nitrogen and react with hydrogen to form ammonia (NH₃).

These processes, taking up around 1% of global energy consumption, are largely fossil fuel-based. Hence, ammonia is the most greenhouse gas-intensive chemical-making reaction globally, totalling roughly 1,5% of total global CO₂ emissions. In addition, demand for ammonia is only expected to increase in the coming years, mainly due to its use in synthetic fertilisers needed to feed an increasing global population.

«One of the major challenges on the climate front, and the energy and food front, is the production of ammonia. Today it is made in some of the largest factories in the world. The only really efficient way to make ammonia is under high temperatures and high pressure and using a carbon-based feedstock,» says Professor Tejs Vegge from DTU Energy and the VILLUM Center for the Science for Sustainable Fuels and Chemicals (V-Sustain). He lead the research along with Professor Ping Chen from the Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences.

«Nature is very good at making ammonia at ambient pressure and temperatures in enzymes like nitrogenase. However, the process is very slow and impossible to scale to industrial production,» says Tejs Vegge.

Potential game-changer

For decades, scientists have been working hard to find new and more sustainable ways to produce ammonia. Together with the team from DICP, Tejs Vegge and his colleagues from DTU, Dr Jaysree Pan and Associate Professor Heine A. Hansen, have introduced a potential game-changer with a new class of complex metal hydride catalysts that had them reach the coveted mild-condition ammonia synthesis. They believe their method could pave the way for new and more sustainable means of ammonia production. Their paper was published in Nature Catalysis.

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Materials provided by Technical University of Denmark. Original written by Tore Vind Jensen. Note: Content may be edited for style and length.