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

Abstract

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 LiPdH0.7 and Li2PdH2 (denoted as [Li–Pd–H]). LiPdH0.7 promotes N2 fixation by LiH forming Li2NH and LiPd, and the subsequent hydrogenation of Li2NH 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–Li2NH composite pair is proposed and demonstrated. An ammonia production rate of 693 μmolNH3 g–1 h–1 was achieved at 300 °C and 1 bar, which is ca. 7 times that of the neat LiH/Li2NH 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.

High‐Throughput Screening of Bicationic Redox Materials for Chemical Looping Ammonia Synthesis

“…be used to capture N 2 (Rxn II) thus regenerating M 𝛼 N 𝛽 to complete the cycle. Similar conversion is also reported in the metal hydride (M-H) based system [31,[39][40][41] shown in Figure 1d. Here, N 2 is reduced by the anionic H − in the metal hydride M-H (Rxn II), thus the loop is dubbed as MH-CL.…”

Facilitating green ammonia manufacture under milder conditions: what do heterogeneous catalyst formulations have to offer?

“…This issue of undesired competitive adsorption can be averted when the nitrogen xation and hydrogenation steps are separated; nitrogen is rst xed in the composite material to yield an imide phase, which is hydrogenated in a second step to yield ammonia. 114,117 A similar two-step pathway for ammonia production has also been identied in composites of manganese nitride and metal (Li or Ba) imides. 118 The looping mode of operation comes with another advantage of ammonia yield not being bound by a thermodynamic equilibrium upper limit.…”

Superior Dehydrogenation Performance of α‐AlH3 Catalyzed by Li3N: Realizing 8.0 wt.% Capacity at 100 °C

“…[16] Thus, further decreasing the dehydrogenation temperature and enhancing the kinetic characteristic are the keys to establishing a mature system. So far, the methods to improve the properties of light metal hydrides mainly include nanocrystallization, [17,18] doping, [19][20][21][22][23] and compositing. [24][25][26][27][28] Among them, catalyst-doping is considered to be the optimal means which presents plentiful superiorities for decreasing metal-H bond energy.…”