Deciphering the synergy between plasma and catalyst support for ammonia synthesis in a packed dielectric barrier discharge reactor

Bhaskar S. Patil (Corresponding author), Alwin S.R. Van Kaathoven, Floran J.J. Peeters, Nikolay Cherkasov, Jürgen Lang, Qi Wang, Volker Hessel (Corresponding author)

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Abstract

Plasma-assisted ammonia synthesis in a packed dielectric barrier discharge (DBD) reactor at atmospheric pressure is presented in this work. A broad range of materials (commonly used as catalyst supports) with various chemical properties (acidic α-Al2O3, anatase TiO2 and basic MgO, CaO), surface area and porosity (α-Al2O3 and γ-Al2O3), dielectric properties (quartz wool, TiO2, and BaTiO3), have been investigated for synergetic effects by packing them in the discharge zone of the DBD reactor. All the materials showed a substantial effect on ammonia production, which can be explained solely as a result of the effect of packing on plasma formation and not by a synergy between plasma and surface catalysis. Size and shape of packing material are found to be the key parameters in enhancing the performance. Quartz wool, closely followed by γ-Al2O3, produces the highest concentration of ammonia at 2900 and 2700 ppm, respectively, due to their ability to generate dense filamentary microdischarges. Particles with a diameter of 200 µm yielded a 64% higher concentration of NH3 than 1300 µm particles - because of amplified electric field strength from increased particle-particle contact points. The specific energy input per unit volume also displayed a significant impact on ammonia production. The process parameters such as N2/H2 feed flow ratio, total flow rate and argon dilution were also investigated. In contradiction to catalytic ammonia synthesis, plasma-assisted synthesis favors a N2/H2 feed ratio 2 instead of the stoichiometric feed ratio of 0.33. At 0.4 l min-1, 3500 ppm of ammonia was produced with an energy efficiency of 1.23 g NH3 kWh-1. Dilution with 2-5 vol% of argon yielded a 2% improvement in the concentration and energy efficiency, which seems insignificant considering the added practical challenges posed by gas separation. To achieve even higher ammonia concentration and energy efficiencies, it is recommended to support transition metal on γ-Al2O3.

Original languageEnglish
Article number144003
Number of pages13
JournalJournal of Physics D: Applied Physics
Volume53
Issue number14
DOIs
Publication statusPublished - 1 Apr 2020

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Keywords

  • Catalyst supports
  • Catalyst-plasma synergy
  • Catalytic DBD reactor
  • Plasma-assisted ammonia synthesis
  • catalyst supports
  • catalytic DBD reactor
  • plasma-assisted ammonia synthesis
  • catalyst-plasma synergy

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