Ammonia (NH3) has played an essential role in meeting the increasing demand for food and the worldwide need for nitrogen (N2) fertilizer since 1913. Unfortunately, the traditional Haber–Bosch process for producing NH3 from N2 is a high energy-consumption process with approximately 1.9 metric tons of fossil CO2 being released per metric ton of NH3 produced. As a very challenging target, any ideal NH3 production process reducing fossil energy consumption and environmental pollution would be welcomed. Catalytic NH3 synthesis is an attractive and promising alternative approach. Therefore, developing efficient catalysts for synthesizing NH3 from N2 under ambient conditions would create a significant opportunity to directly provide nitrogenous fertilizers in agricultural fields as needed in a distributed manner. In this paper, the literature on alternative, available, and sustainable NH3 production processes in terms of the scientific aspects of the spatial structures of nitrogenase metalloclusters, the mechanism of reducing N2 to NH3 catalyzed by nitrogenase, the synthetic analogues of nitrogenase metalloclusters, and the opportunities for continued research are reviewed.
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