Journal
ACS CATALYSIS
Volume 10, Issue 24, Pages 14763-14774Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.0c03166
Keywords
plasma catalysis; ammonia synthesis; in situ surface characterization; computational kinetic modeling; non-thermal plasma
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Funding
- U.S. Department of Energy, Office of Basic Energy Sciences, Catalysis Science Program [DE-FG02-13ER16381]
- U.S. National Science Foundation Graduate Research Fellowship Program [DGE 16-44869]
- CSIRO Research Plus Postdoctoral Fellowship scheme
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Ammonia synthesis by plasma catalysis has emerged as an alternative process for decoupling nitrogen fixation from fossil fuels. Plasma activation can potentially circumvent the limitations of conventional thermocatalytic ammonia synthesis; however, the contribution of different reaction mechanisms to the production of ammonia at the catalyst surface remains unclear. Here, we identify the reaction intermediates adsorbed on gamma-Al2O3-supported Ni and Fe catalysts during plasma-activated ammonia synthesis under various temperatures and reactor configurations using FTIR spectroscopy, steady-state flow reactor experiments, and computational kinetic modeling. Ammonia yield can be influenced by plasma-derived intermediates and their interactions with catalyst surfaces, which lead to different reaction pathways: Ni/gamma-Al2O3 enhances plasma-promoted NH3 production and favors surface-adsorbed NHx species, while Fe/gamma-Al2O3 shows the presence of N2Hy and a lower overall concentration of N-containing adsorbates. Plasma-catalyst interactions are probed to reveal that elevated temperature and plasma irradiation of the surfaces promote NH3 desorption. The direct evidence of catalytic surface reactions occurring during a plasma-activated process provides mechanistic insight into plasma-activated ammonia synthesis.
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