Lithium Palladium Hydride Promotes Chemical Looping Ammonia Synthesis Mediated by Lithium Imide and Hydride

Palladium (Pd) has long been known to be inactive for dinitrogen activation and hence has received little attention for ammonia synthesis. Herein, we report that the reactivity of Pd is changed when reacting with lithium hydride (LiH) forming a series of lithium palladium hydrides such as LiPdH 0.7 and Li 2 PdH 2 (denoted as [Li–Pd–H]). LiPdH 0.7 promotes N 2 fixation by LiH forming Li 2 NH and LiPd, and the subsequent hydrogenation of Li 2 NH and LiPd leads to ammonia and regeneration of LiH and [Li–Pd–H]. Based on these experimental results, an ammonia loop mediated by a [Li–Pd–H]–LiH and LiPd–Li 2 NH composite pair is proposed and demonstrated. An ammonia production rate of 693 μmol NH3 g –1 h –1 was achieved at 300 °C and 1 bar, which is ca. 7 times that of the neat LiH/Li 2 NH pair at 350 °C and 1 bar and 2 times that of the thermocatalytic process catalyzed by Ru/MgO at 300 °C and 10 bar.