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Ammonia is considered a basic building block for fertilizers. Also, it is an economically efficient and technologically suitable solution for energy storage and transportation. Non-thermal plasma-driven catalysis powered by renewable energy is considered as a green alternative to the conventional Haber-Bosch process for ammonia synthesis. The main challenge in this electron-mediated route is the low ammonia synthesis production, given the plasma-induced decomposition of the freshly generated ammonia during the reaction. Herein we report the plasma-assisted ammonia synthesis in a dielectric barrier discharge reactor packed with CC3 crystals, a prototypical porous organic cage, and a molecular-sieve membrane fabricated from the same CC3 material. The CC3 crystals delivered the highest ammonia synthesis rate (0.06 μmol min−1 m−2) compared to other microporous catalysts such as zeolite (SAPO-34) and metal-organic frameworks (ZIF-8, ZIF-67) (below 0.02 μmol min−1 m−2). The CC3 porous cage with well-defined octahedral crystal geometry provides partial protection while the CC3 membrane offers both adsorption and separation effects for the freshly formed ammonia from its in-situ decomposition, securing an excellent ammonia synthesis rate of 20.3 μmol min−1 m−2. The findings from this work unfolds novel insights into rational designs of advanced porous catalyst and membrane for plasma-driven catalytic ammonia synthesis in a sustainable and efficient way.
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Insights on cold plasma ammonia synthesis and decomposition using alkaline earth metal-based perovskites
The synergistic combination of solid catalysts and plasma for the synthesis of ammonia has recently attracted considerable scientific interest. Herein, we explore MgTiO3, CaTiO3, SrTiO3, and BaTiO3 perovskites as effective catalysts for the synthesis and decomposition of ammonia via cold plasma. MgTiO3 perovskite, which contains the most electronegative alkaline metal of all the studied perovskites, resulted in the highest ammonia synthesis rate with a value of 12.16 μmol min−1 m−2, which is around 50 times the value of only plasma, 0.24 μmol min−1. The high electronegativity of Mg can be assisting the dissociation of the triple nitrogen covalent bond. This intrinsic property of Mg perovskite added to the homogeneity of the plasma arising from the dielectric constant value of this perovskite might be synergistically responsible for the high ammonia synthesis rate observed. Interestingly, ammonia production over MgTiO3 perovskite is almost double the performance of traditional oxides and some microporous crystals. We also explored the ammonia decomposition reaction due to the possibility of the importance of the reversible reaction owing to the electron collision with the ammonia molecules formed. Ammonia decomposition increased as plasma power increased. This points out the benefit of running at low plasma power and the need to design plasma reactors where the newly formed ammonia molecules can be removed from the reaction system to avoid further electron collision. The highest ammonia decomposition yield was 44.37% at 20 W corresponding to an energy yield of 5.06 g-NH3 kW h−1.
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- Award ID(s):
- 2203166
- PAR ID:
- 10337533
- Date Published:
- Journal Name:
- Catalysis science technology
- ISSN:
- 2044-4753
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Microporous crystals have emerged as highly appealing catalytic materials for the plasma catalytic synthesis of ammonia. Herein, we demonstrate that zeolitic imidazolate frameworks (ZIFs) can be employed as efficient catalysts for the cold plasma ammonia synthesis using an atmospheric dielectric barrier discharge reactor. We studied two prototypical ZIFs denoted as ZIF-8 and ZIF-67, with a uniform window pore aperture of 3.4 Å. The resultant ZIFs displayed ammonia synthesis rates as high as 42.16 μmol NH3/min gcat. ZIF-8 displayed remarkable stability upon recycling. The dipole−dipole inter- actions between the polar ammonia molecules and the polar walls of the studied ZIFs led to relatively low ammonia uptakes, low storage capacity, and high observed ammonia synthesis rates. Both ZIFs outperform other microporous crystals including zeolites and conventional oxides in terms of ammonia production. Furthermore, we demonstrate that the addition of argon to the reactor chamber can be an effective strategy to improve the plasma environment. Specifically, the presence of argon helped to improve the plasma uniformity, making the reaction system more energy efficient by operating at a low specific energy input range allowing abundant formation of nitrogen vibrational species. KEYWORDS: nonthermal plasma, plasma catalysis, ammonia synthesis, zeolitic imidazolate frameworks, ammonia adsorption effectmore » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/DOI: 10.1039/d1cy00729g
