Effects of oxygen-containing functional groups on the synergy effect in pulsed bipolar plasma-catalytic reactions of volatile organic compounds

Abstract

This study investigated the synergy effect of three high-concentration oxygenated reactants (4000 ppmv), namely 2-butanol, butanone, and ethyl acetate, in pulsed bipolar plasma-catalytic reactions using prepared La_0.7Sr_0.3MnO₃/mullite and isopentane as the catalyst and control compound, respectively. The intensity of the N I 336.62* peak of in situ optical emission spectra was used as the representative intensity to depict the behavior of plasma discharge. The results demonstrate that the variation in trends of plasma discharge with temperature for the four reactants was similar in terms of rising rates, and differences in functional groups did not significantly affect behavior during the reactions. The selected oxygenated organics were clearly more susceptible to catalysis alone and plasma catalysis than the control compound. The results indicate that the relative polarity of oxygenated reactants is a more crucial factor in plasma catalysis than their dielectric constant and ionization potential. A synergy quantitative index (Λ_X) and synergy factor (Ψ_X) were defined to characterize the synergistic behavior of plasma catalysis. The variation of Λ_X with conversion X demonstrates that plasma dissociation was dominant at low conversion rates, and catalysis was dominant at high conversion rates in the plasma-catalytic reaction. The order of Ψ_X values was opposite to that of relative polarities for the reactants. Overall, the plasma-catalytic reaction was construed as the combination of plasma dissociation and synergistic catalysis. Ψ_X was introduced into synergistic catalysis to establish a theoretical formula for the plasma-catalytic reaction. This theoretical formula was proven to be accurate by comparing experimental and theoretical results, and it successfully predicted the conversion–temperature curve of plasma catalysis.