Systematic Study on Nitrogen Dissociation and Ammonia Synthesis by Lithium and Group 14 Element Alloys

The pseudo-catalytic properties of lithium (Li)-based alloys with group 14 elements were investigated for ammonia (NH3) synthesis under ambient conditions. The reaction between the Li alloys and nitrogen (N-2) proceeds below 500 degrees C to form lithium nitride (Li3N). The peak temperature of nitridation was lower in the order of Li-44 Si < Li-4.4 Ge approximate to Li4.4Pb < Li4.4Sn. The N-2 dissociation activity is related to the value of Knight shift observed in the Li-7 solid-state magic angle spinning nuclear magnetic resonance (Li MAS NMR) spectra, indicating that the metallic feature of Li species is an important factor for low-temperature N-2 dissociation. Although the reaction yields for NH3 synthesis were depending on the alloys, NH3 was generated at the same temperature around 240 degrees C because the NH3 formation proceeded by the same reaction between Li3N and hydrogen (H-2), generating lithium hydride (LiH) as a by-product. For all the alloys, LiH desorbs H-2 to form Li alloys with higher Li composition at lower temperature than that of thermal decomposition of pure LiH. In addition, the conventional catalytic process was also investigated under a mixed gas of H-2 and N-2. NH3 was synthesized at 150 and 200 degrees C by using Li4.4Si and Li4.4Ge, respectively.

Automated summary

The pseudo-catalytic properties of lithium-based alloys with group 14 elements were investigated for ammonia synthesis. The reaction temperature and the formation of products depend on the composition of the alloy, and the metallic feature of lithium species plays a significant role in the reaction. Furthermore, ammonia synthesis can also be achieved at lower temperatures through a catalytic process using a mixture of hydrogen and nitrogen.