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.
Keywords: ammonia synthesis; liquid alloy; lithium; molten salt; nitrogen fixation.
© 2021 Wiley-VCH GmbH.