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

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

The ammonia synthesis according to the Haber-Bosch process normally requires temperatures of 400-500 ° C and pressures of 150-300 bar. An open access paper on her work has been published in the journal Angewandte Chemie International Edition.

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

The grinding process in a ball mill activates a catalyst in such a way that it enables ammonia synthesis at significantly lower temperatures and pressures than is required in the tried and tested Haber-Bosch process. © Frank Vinken / MPG

Although optimized for over 100 years, the Haber-Bosch process essentially requires the conditions of its invention: high temperatures of up to 500 ° C and reaction pressures of up to 200 bar in order to achieve reasonable ammonia concentrations at sufficiently high speeds. The most significant innovation was the introduction of ruthenium-based catalysts, which show high activity even at slightly 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 final reactor after the main iron-catalyzed reaction.

… In recent years, mechanochemistry has emerged as a promising alternative strategy for the activation and transformation of molecules. Heterogeneously catalyzed gas phase reactions can also be activated mechanically, which leads to significant increases in activity. Because of its great importance, the mechanocatalytic synthesis of ammonia was also attempted, albeit in fewer than a handful of reports with partially unclear validity of the claims.

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

This study demonstrates the continuous catalytic synthesis of ammonia from the elements, probably similar to the Haber-Bosch process, but at ambient temperature and pressure conditions due to the influence of mechanical forces, despite more than a hundred years of efforts with different approaches.

– Reichle et al.

resources

• S. Reichle, M. Felderhoff, F. Schüth. (2021) “Mechanocatalytic room temperature synthesis of ammonia from its elements to atmospheric pressure”, Angew. Chem. No. Int. Ed., Doi: 10.1002 / anie.202112095