Preparation of the LiGa Intermetallic Alloy by Electrochemical or Thermal Method for Ammonia Synthesis

The Haber–Bosch process is the industrial method for the massive production of ammonia from molecular nitrogen and hydrogen. Yet, its major drawback is the high temperature and pressure condition, causing high energy cost and emissions as well as the large-scale centralized operation. In this work, we have investigated a process consisting of three sequential steps for ammonia synthesis. The first step is the synthesis of LiGa intermetallic alloy by either the electrochemical extraction of metallic lithium from organic solution with a gallium-based liquid metal at room temperature or the direct alloying of lithium and gallium at 800 °C. The second step is the fixation of molecular nitrogen by the LiGa intermetallic alloy at elevated temperatures. The apparent activation energy for N₂ fixation by LiGa was measured to be 0.52 eV. As a complement to the experimental results, the AIMD simulations have been performed to offer a comprehensive and insightful examination of the mechanisms underlying N₂ fixation on the cleaved LiGa (110) surface, highlighting the key role of Li atoms in the N₂ cleavage. The third step is the reaction of the nitrogenized LiGa sample with a proton source to generate ammonia. In addition, we have exploited the use of LiGa for ammonia synthesis in both the 50-h catalytic process and the 120-h chemical looping route, and the corresponding catalytic levels were determined to be 0.349 and 0.204 μmol g_cat⁻¹ h⁻¹, respectively. The performance may be further improved after modification and optimization. This thorough study on LiGa bridges metallurgy and catalysis, and will motivate further research and progress for ammonia synthesis under mild conditions.