Effect of Argon or Helium on the CO₂ Conversion in a Dielectric Barrier Discharge

Abstract

This paper demonstrates that the CO2 conversion in a dielectric barrier discharge rises drastically upon addition of Ar or He, and the effect is more pronounced for Ar than for He. The effective CO2 conversion, on the other hand, drops upon addition of Ar or He, which is logical due to the lower CO2 content in the gas mixture, and the same is true for the energy efficiency, because a considerable fraction of the energy is then consumed into ionization/excitation of Ar or He atoms. The higher absolute CO2 conversion upon addition of Ar or He can be explained by studying in detail the Lissajous plots and the current profiles. The breakdown voltage is lower in the CO2/Ar and CO2/He mixtures, and the discharge gap is more filled with plasma, which enhances the possibility for CO2 conversion. The rates of electron impact excitation–dissociation of CO2, estimated from the electron densities and mean electron energies, are indeed higher in the CO2/Ar and (to a lower extent) in the CO2/He mixtures, compared to the pure CO2 plasma. Moreover, charge transfer between Ar+ or Ar2+ ions and CO2, followed by electron‐ion dissociative recombination of the CO2+ ions, might also contribute to, or even be dominant for the CO2 dissociation. All these effects can explain the higher CO2 conversion, especially upon addition of Ar, but also upon addition of He.

DBD Plasma Assisted CO2 Decomposition: Influence of Diluent Gases

“…The maximum conversion has been observed with Ar dilution, especially at higher discharge power. A similar observation was reported by Ramakers et al [21]. During the present study, ~19.5% CO2 conversion was observed with Ar dilution.…”

“…Ramakers et al studied CO 2 decomposition with diluent gases He and Ar. They showed that at up to 70% diluent gas mixture, He and Ar both have same effect but at higher gas percentage, Ar was more effective than He [21]. Wang et al investigated N 2 and Ar dilution on CO 2 decomposition with 5A molecular sieve packing material and it was reported that N 2 dilution shows better results than Ar, up to 50% diluent gas mixture [22].…”

Plasma-catalyst interaction studied in a single pellet DBD reactor: dielectric constant effect on plasma dynamics

“…This means that using the burning voltage to estimate average electric field strengths (as used in [7,28,34]) and therefore electron energies in the reactor is not a valid approximation.…”

The Production of Ketene and C5O2 from CO2, N2 and CH4 in a Non-thermal Plasma Catalysed by Earth-Abundant Elements: An In-Situ FTIR Study

“…Xu et al [63] interpret such behaviour in terms of an increase in the number density of higher energy electrons in CO 2 non-thermal plasma on dilution with N 2 or Ar. The mean electron energy per molecule ranges from 3.9 to 5.5 eV at the lowest and highest input energies employed by us: given that the threshold energies for the excitation and ionization of CO 2 , N 2 , CH 4 and Ar are all significantly above these values [64][65][66][67], see Table 2, this suggests that electrons in the high energy tail of the distribution must play a significant role.…”

“…36%. The latter effect is unsurprising as the ionization energy of Ar is high, 15.76 eV [68] and it is generally accepted that, at the high concentrations of N 2 employed (70-90%), metastable N 2 states will be primarily responsible for the conversion of both CO 2 and CH 4 [64,68]:…”