Dinitrogen fixation mediated by lanthanum hydride

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 Nfixation and hydrogenation to ammonia. Herein, we report that rare earth metal hydrides such as lanthanum hydride can also fix Neither by heating to 200 °C or ball milling under ambient Npressure and temperature. The Nfixation 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 Nactivation possibly mediated by the lanthanum atoms. It is observed that N–H bond is not formed during the Nfixation 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.

Mild-condition synthesis of A2ZnH4(A = K, Rb, Cs) and their effects on the hydrogen storage properties of 2LiH-Mg(NH2)2

In this paper, A2ZnH4(A = K, Rb and Cs) have been synthesized for the first time by a new approach involving in two-step reactions, in which the target samples can be produced under mild conditions(160 ℃ for 4 h). What’s more, the additive effects of A2ZnH4 on the hydrogen storage properties of 2LiH-Mg(NH2)2 composite have been investigated systematically. Experimental results show that K2ZnH4 has the best comprehensive modification effects among these hydrides. The 2LiH-Mg(NH2)2-0.1 K2ZnH4 sample shifts dehydrogenation peak temperature downwards by ca. 30 ℃ as compared to the pristine sample. In addition, about 70% extent of the theoretical hydrogen is able to desorb from the 0.1 K2ZnH4 doped sample at 140 ℃ within 2 h, however, only 20% extent of hydrogen is liberated from the pure sample under the same conditions. The improved desorption kinetics is indicated by the reduced dehydrogenation activation energy(Ea), the Ea of the 0.1 K2ZnH4 doped sample is around 68 ± 1.0 kJ mol-1 which is 28% lower than that of the pristine one. Furthermore, the dehydrogenation mechanism of the K2ZnH4 doped sample has been proposed.