The dynamic evolution and interaction with dielectric material of the discharge in packed bed reactor

In this paper, dielectric columns with different dielectric constants are employed as dielectric materials in the packed bed reactor to investigate the dynamic behaviors of plasma interaction processes. The effects of the dielectric constants (zirconia: ϵ = 25 and PTFE: ϵ = 2.5) on the production of reactive species are studied for plasma catalysis applications. Comparison studies of discharge images, electrical characteristics, discharge dynamic evolution and spatial-temporal resolved optical emission spectroscopy are carried on when zirconia and PTFE columns are employed. The results show that there are four discharge processes existing in the packed bed reactor: surface streamer on the dielectric column, local discharge at the contact point, surface discharge on the grounded dielectric plate, and the volume discharge. The production of reactive species such as N₂(C³П_u), N₂ ⁺(B²Σ_u ⁺) and O(3p⁵P) depend on the discharge processes to a great extent. The production of the N₂ ⁺(B²Σ_u ⁺) always accompanies the formation of the streamer by electrons direct impact process to excite the ground state nitrogen molecules to N₂ ⁺(B²Σ_u ⁺). The O(3p⁵P) is generated in two different ways, which plays a major role during the voltage pulse raising and falling time, respectively. The first way is the direct and fast one-step ionization and excitation by high energy electrons with O₂. The second way is the energy transfer from the nitrogen metastable N₂(A³Σ_u ⁺) and energetic electrons, in which the O is first ionized from O₂ and then excited to O(3p⁵P). Furthermore, compared with a zirconia column, a PTFE column is more conductive to the generation of reactive species.