Non-thermal plasma coupled with MOx/γ-Al2O3 (M: Fe, Co, Mn, Ce) for chlorobenzene degradation: Analysis of byproducts and the reaction mechanism

Abstract

Chlorinated volatile organic compounds (VOCs) such as chlorobenzene pose serious human health and environmental risks, but are resistant to elimination techniques that are traditionally applied to Cl-free VOCs. Non-thermal plasma (NTP) offers a promising technique to decompose chlorobenzene, but its application remains limited owing to low COx selectivity and the generation of toxic byproducts. To address these problems, this study investigated chlorobenzene degradation in NTP coupled with MOx/γ-Al2O3 (M: Fe, Co, Mn, Ce) catalysts. The combination of NTP with MOx/γ-Al2O3 remarkably improved the removal efficiency (RE), mineralization rate (MR), Cl selectivity (SCl) and energy yield (EY) of chlorobenzene abatement, and decreased the production of residual O3. CoOx/γ-Al2O3 exhibited the best performance among these tested catalysts with higher RE, MR, SCl and EY by 26.06%, 25.52%, 33.03% and 2.41 g/kWh, respectively, at 510 J/L, compared with those of the NTP alone system. Several catalyst characterizations were applied to explore the relation between the catalyst characteristics and chlorobenzene abatement efficacy in NTP. The results indicate that the NTP catalytic oxidation of chlorobenzene strongly depends on the reducibility and acidity of the MOx/γ-Al2O3 samples, whereas the textural properties of the catalysts exert a limited influence on chlorobenzene degradation. High-resolution gas chromatography and high-resolution mass spectrometry analyses verified for the first time that PCDD/Fs were generated during chlorobenzene degradation in NTP catalytic reactions. A plausible decomposition mechanism of chlorobenzene in the NTP catalytic system is speculated according to the organic intermediates generated during chlorobenzene decomposition.