Hydride-enhanced plasma catalysis enables ultrahigh-rate ammonia synthesis at room temperature and atmospheric pressure

doi:10.1016/S1872-2067(26)65089-9

Abstract

Abstract:

The decarbonization of the ammonia (NH₃) synthesis industry demands the development of energy-efficient and sustainable processes. Among various emerging approaches, non-thermal plasma (NTP) catalysis shows significant promise for overcoming the sluggish kinetics of nitrogen (N₂) activation under mild conditions while minimizing carbon emissions. Growing evidence suggests that plasma-derived hydrogen radical (H•) can serve as powerful reducing agent and direct hydrogen source to activate N₂ molecules in the gas phase. However, the efficient and sustained generation of H• species typically relies on high-power plasma dischages, leading to excessive energy consumption. In this study, we introduce a metal hydride-enhanced plasma catalysis strategy, in which TiH₂, CaH₂, and LiH act as hydrogen donors, releasing lattice hydrogen atoms as H• radicals while generating hydrogen vacancies on the surface. These vacancies are rapidly replenished by H₂ molecules, establishing a self-sustaining hydrogen-release/replenishment cycle that continuously supplies reactive H• species. As a result, this approach achieves an untrahigh NH₃ yield of 360.9 mg·h^-1·g^-1 and an energy efficiency of 9.02 g·kWh^-1 at room temperature and atmospheric pressure, surpassing most reported catalytic systems. Mechanistic studies reveal that the release of lattice hydrogen is the rate-determining step, while N₂ hydrogenation proceeds with a remarkably low energy barrier of 0.123 eV. These findings highlight the potential of metal hydrides as effective catalysts for plasma catalysis and provide valuable guidelines for the development of future catalysts aimed at energy-efficient activation of inert molecules.

Key words: Ammonia synthesis, Nitrogen reduction, Plasma catalysis, Nonthermal plasma, Catalytic conversion

Shijian Luo, Hao Chen, Yuran Yang, Yang Song, Yongduo Liu, Daojun Long, Siguo Chen, Zidong Wei. Hydride-enhanced plasma catalysis enables ultrahigh-rate ammonia synthesis at room temperature and atmospheric pressure[J]. Chinese Journal of Catalysis, 2026, 88: 269-278.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(26)65089-9

https://www.cjcatal.com/EN/Y2026/V88/I9/269

Figures/Tables 6

Fig. 1. The mechanism of H• formation on the surfaces of oxide and hydride catalysts under plasma discharge conditions.

Fig. 2. XRD patterns of TiH2 (a), CaH2 (b), and LiH (c). (d) NH3 yield of hydrides and catalyst-free conditions at varying input powers. (e) Energy efficiency of hydrides and catalyst-free conditions at varying specific energy inputs. (f) The modified Arrhenius plots for the hydrides systems. (g) Reported energy efficiency and NH3 concentration in the plasma-catalytic systems over different catalysts. (h) Comparison of energy efficiency and NH3 concentration in state-of-the-art sustainable ammonia synthesis technologies.

Fig. 3. (a) Stability of hydride catalysts over a 500-h reaction test. (b) Collection efficiency of solid NH4Cl product using the rotary evaporation method. (c) XRD patterns of NH4Cl product obtained after 500 h of reaction with hydride catalysts. EPR spectra (d) and PALS results (e) of hydride catalysts after 500 h of reaction. (f) Intensities of I1, I2, and I3 in the hydrides obtained via PALS.

Fig. 4. NH3 yields (a) and EPR spectra (b) of the fresh hydride catalysts and they were alternately exposed to N2, H2, and H2-N2 plasma at 40 W. (c) DMPO-involved EPR spectra of the plasma-induced gas species with the hydride catalysts under varying plasma conditions.

Fig. 5. (a) Isotope tracking experiments for lattice hydrogen atoms in the hydride catalysts. Kinetic isotope effects (H/D) on NH3 synthesis rates for TiH2 (b), CaH2 (c), and LiH (d). The reaction rate dependence on N2 partial pressure (e) and H2 partial pressure (f) under plasma-catalytic conditions for various hydride catalysts.

Fig. 6. (a) Schematic diagram of the model for constructing one to three vacancies on the hydride surfaces. (b) Vacancy formation energies for TiH2, CaH2 and LiH. (c) Free-energy diagram for the plasma-catalytic H-release/H-refill cycle using hydride catalysts with a single vacancy. (d) Free-energy diagram for the plasma-catalytic H-release/H-refill cycle using hydride catalysts with hydrogen-vacancy clusters. (e) Free-energy diagram illustrating the H• radical-dominated N2 reduction pathway via plasma-induced gas reactions.

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