Spatially and temporally non-uniform plasmas: microdischarges from the perspective of molecules in a packed bed plasma reactor

Abstract

Dielectric barrier discharges (DBDs) typically operate in the filamentary regime and thus exhibit great spatial and temporal non-uniformity. In order to optimize DBDs for various applications, such as in plasma catalysis, more fundamental insight is needed. Here, we consider how the millions of microdischarges, characteristic for a DBD, influence individual gas molecules. We use a Monte Carlo approach to determine the number of microdischarges to which a single molecule would be exposed, by means of particle tracing simulations through a full-scale packed bed DBD reactor, as well as an empty DBD reactor. We find that the fraction of microdischarges to which the molecules are exposed can be approximated as the microdischarge volume over the entire reactor gas volume. The use of this concept provides good agreement between a plasma-catalytic kinetics model and experiments for plasma-catalytic NH3 synthesis. We also show that the concept of the fraction of microdischarges indicates the efficiency by which the plasma power is transferred to the gas molecules. This generalised concept is also applicable for other spatially and temporally non-uniform plasmas.

On the mechanism for the plasma-activated N2 dissociation on Ru surfaces

“…It should be noted that the plasma characteristics in a DBD reactor are stochastic (e.g. varying in time and space), and the densities of plasma species vary during the streamer discharges and the afterglow [54,55]. As the catalyst material determines the sticking probability of S N2(ex) , this analysis is valid for Ru exclusively.…”

Full-wave and plasma simulations of microstrip excited, high-frequency, atmospheric pressure argon microdischarges

“…An excellent Monte-Carlo based study demonstrating the complexity of PB-DBDs physics (including gas flow phenomena) as well as the sensitivity of common modeling assumptions can be found in Ref. [31]. The validity of 0D plasma kinetics models would be greatly enhanced if the necessary input parameters would be based on accurately predicted, non-uniform and timedependent in nature plasma densities, discharge power and/or spatiotemporal evolution of generated species.…”

CO2 dissociation in a packed bed DBD reactor: effect of streamer discharge

“…However, with conventional beads as packing material in PB-DBD, it is difficult to establish a controllable gas discharge characteristic, which is attributed to the complex electric field distribution on the particle surface and irregular discharge channels. In addition to the particle physical characteristics, such as dielectric constant [24,25], particle size [26,27] and morphology [5,28,29], the spatial position relationship between particles is also an important factor affecting the electric field distribution on the surface [18,22,30,31]. However, the particle position and discharge channel have great uncertainties in particle-packed PB-DBD [10,[32][33][34].…”