Plasmas for Ammonia Synthesis*

J.B. HALL, Z. LIN, S. ABE, Z. CHEN, S. JAISWAL, A. DIALLO (PPPL), B.E. KOEL Princeton U. - 

A zero-dimensional (0D) kinetic model has been developed for N₂-H₂-noble gas (He or Ar) atmospheric pressure plasmas based on the ZDPlasKin plasma kinetics solver [1] to understand both the volumetric and surface (Ru or Fe on ??-Al₂O₃) reactions related to plasma-assisted catalysis as a potentially lower energy alternative to the standard Haber-Bosch process for ammonia synthesis. Results have shown that the dominant metastables, Ar_meta (1s⁵ and 1s³) and He(2³S), formed via electron-impact excitation, can support N atom and ion formation through the reactions N₂ + Ar_meta → 2N + Ar and N2 + He(2³S) →  N + N⁺ + He + e. These N species play an important role in NH₃ formation via N + H2^* →NH + H (H2^* is an electronically excited species) in our dielectric barrier discharge reactor for electron number densities 10⁶-10¹⁰ cm^-3. Effects of the neutral gas flow rates for both He and Ar on the plasma chemistry are also investigated. We pair the He modeling results with a He Collisional-Radiative (CR) model for plasma diagnostics and compare with He line intensity ratios experimentally obtained by optical emission spectroscopy. 

[1] S. Pancheshnyi et al., 2008 Computer code ZDPlasKin (www.zdplaskin.laplace.univ-tlse.fr)