Progress of metal hydrides, amides and imides for ammonia synthesis and decomposition
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GRAPHICAL ABSTRACT
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PUBLIC SUMMARY
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The versatile chemical interconversions of alkali/alkaline metal hydrides, amides, and imides exhibit with N2, H2, or NH3 are presented.
The recent progress in utilizing hydrides, amides or imides for catalytic and chemical looping processes in ammonia synthesis and decomposition are reviewed.
The unique roles of hydrides, amides, and imides in activating and transforming N2 and NH3, their distinct reaction mechanisms are discussed.
The current challenges and future prospects are analyzed.
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ABSTRACT
Ammonia, as a key feedstock for nitrogen fertilizers, also plays a crucial role as an energy and hydrogen carrier in the storage and conversion of renewable energy. The synthesis and decomposition of ammonia are central to realizing its full potential in these applications. Recent studies have highlighted the versatile chemical interconversions of alkali/alkaline metal hydrides, amides, and imides exhibit with N2, H2, or NH3. Building on these findings, a series of highly efficient catalysts and novel processes for ammonia synthesis and ammonia decomposition have been developed. This review comprehensively summarizes recent progress in utilizing these compounds as functional materials for catalytic and chemical looping processes in ammonia synthesis and decomposition. Special attention is given to the unique roles of hydrides, amides, and imides in activating and transforming N2 and NH3, their distinct reaction mechanisms, and discuss the current challenges and future prospects of these materials in ammonia synthesis and decomposition process. -
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Feng S., Gao W., Guo J., et al. (2025). Progress of metal hydrides, amides and imides for ammonia synthesis and decomposition. The Innovation Energy 2:100122. https://doi.org/10.59717/j.xinn-energy.2025.100122
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Feng S., Gao W., Guo J., et al. (2025). Progress of metal hydrides, amides and imides for ammonia synthesis and decomposition. The Innovation Energy 2:100122. https://doi.org/10.59717/j.xinn-energy.2025.100122
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Figure 1.
Interconversion between metallic lithium and its hydride, nitride, amide, imide, and nitride-hydride.
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Figure 2.
Scaling relations and volcano plot on transition metal catalysts in ammonia synthesis reaction
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Figure 3.
(A) The ammonia production performance comparison of 3d TM(N) with LiH as a function of temperature. (B) The ammonia production performance of 3d TM(N) (from V to Ni) with or without LiH at 300°C. (C) The ammonia production performances of Cr-, Mn-, Fe- and Co-LiH composites, Ru/MgO and Cs-Ru/MgO catalysts at 250 and 300°C.53 (D) The ammonia production performance comparison of KH0.19C24 and Ru/MgO as a function of temperature.109 (E) Proposed reaction mechanism of ammonia synthesis on 3d TM(N)-LiH composite catalysts.53 (F) Mass spectrum of the species produced by pulsed laser vaporization of Fe-LiH in the presence of a helium and N2 carrier gas.112
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Figure 4.
(A) Ammonia synthesis rates of various Ru catalysts as a function of temperature. (B) Effluent NH3 concentration over the Ba2RuH6/MgO catalyst at different temperatures. (C) Calculated free-energy pathway for the associative mechanism of ammonia synthesis over Ru complex hydride catalysts. Color code: Li: white, Ru: red, H:yellow, N: blue.56
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Figure 5.
Schematics for catalytic ammonia synthesis over
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Figure 6.
(A) Mass spectrometry (MS) profiles of LiH under a flow of Ar with or without UV illumination at room temperature. The insets are the digital photos of LiH with or without UV illumination. (B) EPR spectra of LiH with or without illumination. (C) The photocatalytic ammonia synthesis rate of LiH under UV illumination. (D) Schematics for charge carrier separation processes during the photolysis of LiH.129
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Figure 7.
(A) Three different types (a: H2O-CL, b: H2-CL, c: AH-CL) of CLAS. M, and A denote metal and alkali/alkaline earth metal, respectively. (B) Thermodynamic analyses of steps I and II in AH-CL. (C) Different TM catalyzed nitridation of BaH2. (D) Comparison of NH3 production rates of Ni-catalyzed AH-CL (1bar) with some efficient catalysts in the conventional thermocatalytic process (10 bar).62
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Figure 8.
(A) Schematic diagram of CLAS mediated by MnNx-BaNH composite N carrier.63 (B) N2-TPR of plain and cobalt-composited LiH and Li4NH151. (C) Reaction yield obtained by the TG-MS experiments for LiH with or without Li2O.152 (D) The combination of liquid Li-Sn alloy and molten eutectic LiCl-KCl salt for CLAS.153 (E) Schematic diagram of CLAS mediated by Zn-LiH-Li2NH.154 (F) Conceptual cycle for Electro-driven CLAS process mediated by LiH/Li2NH.159 (G) Conceptual cycle for Plasma-driven CLAS mediated by NaH/NaNH2.160 (H) Conceptual cycle for Photo-driven CLAS process mediated by LiBaH3.161
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Figure 9.
(A) Equilibrium conversion of NH3 at different temperatures and 1 atm. (B) Experimental rate of ammonia decomposition over various catalysts as a function of the reaction energy of dissociative N2 adsorption.166 (C) The effect of alkali/alkaline earth metal amides/imides of the ammonia decomposition rates with selected transition metals.86 (D) Schematic diagram of ammonia decomposition mechanism over TM-Li2NH composite catalysts.86 (E) Simplified scheme outlining the catalytic ammonia decomposition mechanism of Li2NH.171 (F) Schematic diagram of ammonia decomposition over Ni/CaNH.78
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Figure 10.
(A) Schematic diagram of CLADH mediated by alkali metals and corresponding alkali metal amides pairs. (B) Thermodynamic analyses of equation 7 and equation 8 of CLADH. The solid lines represent the temperature dependences of Gibbs free energy (ΔG) for the decomposition of NaNH2 and KNH2. The dashed lines represent the temperature dependences of ΔG for Na and K ammoniation.179 (C) Temperature-dependent hydrogen production rates of CLADH. (D) The Arrhenius plots of temperature-dependent hydrogen production rate over NaNH2 and KNH2 with or without MnN. (E) Application scenario of the CLADH process for hydrogen production and solar energy storage.179
