Ammonia Synthesis via Chemical Looping Using Nano-Confined Lithium Hydride in Alloy Matrix

Recently, the kinetic improvement of the nitrogenation reaction of lithium hydride (LiH) to form lithium imide (Li2NH) by adding a scaffold was reported. The scaffold prevents agglomeration of Li2NH and maintains the activity of LiH, achieving a reduction in reaction temperature and an increase in reaction rate. In this work, a Li–Si alloy, Li22Si5, was used as a starting material to form nano-sized LiH dispersed in a Li alloy matrix. Lithium nitride (Li3N) is generated by the reaction between Li22Si5 and N2 to form Li7Si3, and then Li3N is converted to LiH with ammonia (NH3) generation during heat treatment under H2 flow conditions. Since Li3N is formed at the nano-scale on the surface of alloy particles, LiH generated from the above nano-Li3N is also nano-scale. The differential scanning calorimetry results indicate that direct nitrogenation of LiH in the alloy matrix occurred from around 280 °C, which is much lower than that of the LiH powder itself. Such a highly active state might be achieved due to the nano-crystalline LiH confined by the Li alloy as a self-transformed scaffold. From the above experimental results, the nano-confined LiH in the alloy matrix was recognized as a potential NH3 synthesis technique based on the LiH-Li2NH type chemical looping process.