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[Display omitted] • An initial reaction mechanism for plasma-assisted steam reforming of toluene. • Over 60 % toluene was converted into small molecules (H 2 , CO, C 2 H 2) at 300 °C. • Combining kinetic modeling of plasma reactions and quantitative analysis of OES. • Interaction mechanism of plasma species and radicals was unveiled. • Synergy rules for plasma and thermal processes have been preliminarily obtained. Plasma-enhanced reforming has been widely studied as an efficient technology for online tar removal. By combining reforming experiments with kinetic modeling and in-situ optical emission spectrometry (OES) analysis, interaction mechanism and coupling rules of plasma/thermal reactions during plasma-assisted steam reforming of toluene were well explored in this study. A chemistry model was innovatively developed for plasma-assisted steam reforming of toluene, and predicted experimental results under different operations conditions with superb agreements. The rate of production and sensitivity analysis implied that OH, H and N 2 * mainly contributed to primary toluene conversion, while the electronic attachment dissociation of H 2 O, H addition onto benzene ring and benzyl oxidation by OH were the most enhancing-sensitive reactions. Resultantly, toluene conversion was greatly increased with steam addition before Vf H2O = 10 %, but after which Vf H2O increase deteriorated the reforming performance due to the inhibition of E-N 2 collision by high Vf H2O. As temperature increased, plasma and thermal synergistically promoted reforming performance before 300 °C, at which > 60 % toluene was converted into small molecules such as CO, H 2 and C 2 H 2, with yields of 23.6 %, 9.4 % and 16.3 % correspondingly at 12 kJ/L, but further temperature increase would not benefit due to the reduced discharge field strength at higher temperatures, being confirmed by the decreased relative intensity of OH, CN feature bands on OES. It was initially proposed that non-thermal plasma governed the reforming process at T < 300 °C, and thermal reactions predominated at T > 500 °C after a transition region (300 ∼ 500 °C). Increase of input energy caused higher discharge field strength, promoted the electronic collision ionization or dissociation of N 2 and H 2 O, thus enhanced toluene conversion and gas yields. A detailed reaction pathway has also been clarified. [ABSTRACT FROM AUTHOR]

Non-thermal plasma (NTP) is emerging as an attractive method for decomposing volatile organic compounds (VOCs). In this paper, to study toluene degradation mechanism in air/H 2 O dielectric barrier discharge (DBD) plasma, optical emission spectrometry (OES) was employed to in-situ monitor active species in plasma, with the permanent degradation products being detected by on-line mass spectrometry under various operations. A detailed kinetic model of NTP with incorporation of non-constant electron filed and thermal effects has also been established. A toluene degradation efficiency > 82% could be achieved at P = 115 W, C in, toluene = 1000 ppm. The relative spectrum intensity of excited OH, O, H and N 2 (A3Σ+ u) increased with increase of discharge power and was decreased at higher gas flowrates. Toluene degradation was mainly induced by oxidation of OH and O at afterglow stage, while part of toluene was decomposed by attack of electrons and reactive particles N 2 (A3Σ+ u) in discharge stage. A toluene degradation pathway has been proposed as: toluene→benzyl→benzaldehyde→benzene→phenoxy→cyclopentadiene→polycarbenes/alkynol→CO 2 /H 2 O. Benzoquinone, benzaldehyde, cyclopentadiene and cyclopentadienyl are supposed to be important intermediates for the ring-opening of toluene. Clarification of toluene degradation behaviors at discharge and afterglowing stage could provide new insights for plasma-catalytic process in future. [Display omitted] • Comprehensive explorations on plasma-based toluene degradation mechanism. • Plasma kinetic model with incorporation of non-constant electric field and thermal effects. • Detailed toluene degradation pathways in pulsed air/H 2 O DBD plasma. • A toluene degradation efficiency > 82% was achieved at P = 115 W without catalyst. [ABSTRACT FROM AUTHOR]