Lithium-based Loop for Ambient-Pressure Ammonia Synthesis in a Liquid Alloy-Salt Catalytic System

The Haber-Bosch process for ammonia (NH₃ ) production in industry relies on high temperature and high pressure and is therefore highly energy intensive. In addition, the activity of the solid transition metal-based catalysts used is typically limited by the scaling relation between activation barrier for N₂ dissociation and nitrogen-binding energy. Here, an innovative Li-based loop in a liquid alloy-salt catalytic system for ambient-pressure NH₃ synthesis from N₂ and H₂ was developed. The looping process consisted of three reaction steps taking place simultaneously. The first step was the nitrogen fixation by Li in the liquid Li-Sn alloy to form lithium nitride (Li₃ N), which floated up and dissolved into the molten salt. The second step was the hydrogenation of the Li₃ N to produce NH₃ and lithium hydride (LiH) in the molten salt. The third step was the decomposition of the LiH to regenerate Li in the presence of Sn. An average NH₃ yield rate of 0.025 μg s^-1 was achieved in an 81 h test at 510 °C and ambient pressure. The floating and dissolution of Li₃ N realized in the liquid catalytic system enabled circumventing the scaling relation exerted on Li, and the remarkable properties of liquid alloy and molten salt offered extraordinary advantages for NH₃ synthesis at ambient pressure.