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 (NH 3 ) synthesis under ambient conditions. The reaction between the Li alloys and nitrogen (N 2 ) proceeds below 500 °C to form lithium nitride (Li 3 N). The peak temperature of nitridation was lower in the order of Li 4.4 Si < Li 4.4 Ge ≈ Li 4.4 Pb < Li 4.4 Sn. The N 2 dissociation activity is related to the value of Knight shift observed in the 7 Li solid-state magic angle spinning nuclear magnetic resonance ( 7 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 NH 3 synthesis were depending on the alloys, NH 3 was generated at the same temperature around 240 °C because the NH 3 formation proceeded by the same reaction between Li 3 N 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 . NH 3 was synthesized at 150 and 200 °C by using Li 4.4 Si and Li 4.4 Ge, respectively.