Researchers report mechanocatalytic synthesis of ammonia at room temperature and atmospheric pressure

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Researchers at the Max Planck Institute for Coal Research (Max-Planck-Institut für Kohlenforschung) report the mechanocatalytic synthesis of ammonia on a cesium-activated iron catalyst under mild conditions – room temperature and pressures up to at 1 bar.

The synthesis of ammonia via the Haber-Bosch process normally requires temperatures of 400 to 500 ° C and pressures of 150 to 300 bar. An open access article on their work is published in the journal Angewandte Chemie international edition.

Ammonia is the basis of all nitrogenous fertilizers and is the subject of discussion as a hydrogen transport and storage molecule in future energy systems. It is estimated that currently around 2% of the world’s energy demand is used for the synthesis of ammonia.

The grinding process in a ball mill activates a catalyst in such a way that it facilitates the synthesis of ammonia at a temperature and pressure well below those required in the well-established Haber-Bosch process. © Frank Vinken / MPG


Although optimized for more than 100 years, the Haber-Bosch process still essentially requires the conditions applied to its invention: high temperatures of up to 500 ° C and reaction pressures of up to 200 bars to reach concentrations. of reasonable ammonia at sufficiently high velocities. The most important innovation was the introduction of ruthenium-based catalysts, showing high activity also at somewhat lower pressures. Nevertheless, ammonia production is still dominated by the iron-catalyzed Haber-Bosch process, with the ruthenium catalyst being used in some plants in a last reactor downstream of the main iron-catalyzed reaction.

… In recent years, mechanochemistry has evolved as a promising alternative strategy for the activation and transformation of molecules. Likewise, heterogeneously catalyzed gas phase reactions can be activated mechanically, resulting in significant improvements in activity. Due to the great importance, the mechanocatalytic synthesis of ammonia has also been attempted, although in less than a handful of reports with partly uncertain validity of the claims.

… We have developed a system for the mechanocatalytic synthesis of ammonia from its elements operating at room temperature and up to atmospheric pressure. While several systems have been identified that led to the formation of ammonia, the most promising systems consist of a mixture of iron with small amounts of elemental cesium. This catalytic system operates both in batch conditions and in a continuous process for more than 60 h, leading to the continuous formation of ammonia at values ​​up to 0.26 vol. %.

This study demonstrates the continuous catalytic synthesis of ammonia from the elements in a manner likely similar to the Haber-Bosch process, but under conditions of ambient temperature and pressure due to the influence of mechanical forces, which remained elusive despite over a hundred years of effort through different approaches.

—Reichle et al.

Resources

  • S. Reichle, M. Felderhoff, F. Schüth. (2021) “Mechanocatalytic synthesis at room temperature of ammonia from its elements up to atmospheric pressure”, Angew. Chem. Int. Ed., doi: 10.1002 / anie.202112095


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