Dissociation against oxidation kinetics for the conversion of VOCs in non-thermal plasmas of atmospheric gases*
Laboratoire de Physique des Gaz et des Plasmas, Université Paris-Sud, CNRS, Université Paris-Saclay, 91045 Orsay cedex, France
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Revised: 18 January 2016
Accepted: 25 January 2016
Published online: 8 August 2016
The kinetics of four volatile organic compounds (VOCs) (propene, propane, acetaldehyde, acetone) were studied in plasmas of atmospheric gases using a photo-triggered discharge (homogeneous plasma) or a dielectric barrier discharge (filamentary plasma). It was shown for the homogeneous plasma that quenchings of nitrogen metastable states, A3Ʃ+u and the group of singlets a' 1Ʃ-u, a 1Πg and w 1∆u, are important processes for the decomposition of such molecules. Recent measurements of the H2 concentration produced in the N2/C3H6 mixture emphasize that the hydrogen molecule can be an exit route for propene dissociation. It is also found that H2 and CO molecules are efficiently produced following the dissociation of CH3COCH3 and the subsequent chemical reactivity induced by radicals coming from acetone. Addition of oxygen to a N2/VOC mixture can change drastically the kinetics. However, the quenching processes of N2 metastables by the VOC are always present and compete with oxidation reactions for the conversion of the pollutant. At low temperature, oxidations by O or by OH are not always sufficiently effective to induce an increase of the molecule decomposition when oxygen is added to the mixture. In particular, the presence of O2 has a detrimental effect on the acetone removal. Also, as evidenced for acetaldehyde and propane, some kinetic analogies appear between filamentary and homogeneous plasmas.
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