Dinitrogen fixation mediated by lanthanum hydride

Abstract

Dinitrogen fixation is one of the key reactions in chemistry, which is closely associated with food, environment, and energy. It has been recently recognized that the hydride materials containing negatively charged hydrogen (H‾) show promises for N2 fixation and hydrogenation to ammonia. Herein, we report that rare earth metal hydrides such as lanthanum hydride can also fix N2 either by heating to 200 °C or ball milling under ambient N2 pressure and temperature. The N2 fixation by lanthanum hydride may proceed via an intermediate lanthanum hydride-nitride (La-H-N) structure to form the final lanthanum nitride product. The hydride ion functions as an electron donor, which provides electrons for N2 activation possibly mediated by the lanthanum atoms. It is observed that N–H bond is not formed during the N2 fixation process, which is distinctly different from the alkali or alkaline earth metal hydrides. The hydrolysis of La-H-N to ammonia is feasible using water as the hydrogen source. These results provide new insights into the nitrogen fixation by hydride materials and more efforts are needed for the development of rare earth metal-based catalysts and/or nitrogen carriers for ammonia synthesis processes.