Molten multi-phase catalytic system comprising Li-Zn alloy and LiCl-KCl salt for nitrogen fixation and ammonia synthesis at ambient pressure

Ammonia (NH3) is one of the most important synthetic inorganic commodities. The current industrial NH3 production is dominated by the Haber-Bosch process with high energy cost and CO2 emission as well as the need for large-scale centralized operation. Liquid metals and molten salts have recently emerged as promising catalytic materials for NH3 synthesis. Herein, we present a molten system comprising Li-Zn alloy and eutectic LiCl-KCl salt for effective NH3 synthesis at 400 degrees C and 1 bar. The 70 mol% Li-Zn liquid alloy activates N2 dissociation more easily than the pure liquid Zn and the 60 mol% Li-Sn liquid alloy. Effective N2 fixation by the liquid Li-Zn alloy is followed by the hydrogenation of Li3N dissolved in the molten salt above. For the first time, this work reports a volcano-type relationship between the Li3N concentration in the molten salt and the NH3 synthesis rate when feeding H2 to the molten salt. Ab initio molecular dynamics simulations suggest that, within this system, both N2 cleavage and Li3N hydrogenation are quite reactive. Through combined experiments and simulations, this work unravels the molecular mechanisms of nitrogen fixation and ammonia synthesis in the liquid alloy-salt catalytic system, and also demonstrates effective strategies for improving the ammonia synthesis rate. Such a hybrid molten catalytic system offers a promising solution for distributed NH3 production with low energy cost and CO2 emission. Through combined experiments and simulations, we unraveled the molecular mechanisms of nitrogen fixation and ammonia synthesis in the molten catalytic systems.