Study On Plasma-catalytic Oxidation Of Benzene

The emission of volatile organic compounds?VOCs?into the atmosphere,which caused health and environmental problems,is becoming increasingly serious.In recent years,non-thermal plasma-catalytic technology for decomposition of low-concentration benzene has been widely concerned as an effective technique.The aim of this study is to develop a benzene removal technology using non-thermal plasma-catalytic oxidation,and investigated the decomposition properties of benzene with plasma hybrid with CeO₂/y-Al₂O₃,Au/?-Al₂O₃,Ag/?-Al₂O₃,Pt/?-Al₂O₃ catalysts.Firstly,the mechanism of plasma-catalytic oxidation of benzene over CeO₂/?-Al₂O₃ catalyst was studied in detail.A tube dielectric barrier discharge?DBD?reactor with CeO₂/?-Al₂O₃ catalyst was used to decompose benzene.Secondly,plate DBD reactors with noble metal catalysts?Au/?-Al₂O₃,Ag/?-Al₂O₃,and Pt/?-Al₂O₃?to decompose benzene were studied.The main findings are as follows:?1?Plasma hybrid with CeO₂/?-Al₂O₃ catalysts has obvious synergistic effect on the decomposition of benzene.And 5.0wt%CeO₂/?-Al₂O₃ catalyst has the best synergistic effect with plasma in all CeO₂/?-Al₂O₃ catalysts.This is consistent with the characterization results of X-ray diffraction?XRD?and energy dispersive spectrometer?EDS?.The removal ratio of benzene increased with increasing SED and decreased with increasing initial concentration.When SED increased from 20.8 J/L to 86.7 J/L,the benzene removal ratio increased from 80%to 99%,and the CO₂ selectivity increased from 20.5%to 114%;when the initial concentration of benzene increased from 50 ppmv to 300 ppmv,CO₂ selectivity increased slightly.When reaction temperature was increased,the removal ratio of benzene decreased,but CO₂ selectivity increased.O₂ concentration was increased,the removal ratio of benzene increased.However,which had little effect on benzene removal and CO_x selectivity.H20 inhibitd benzene decomposition;however,it improves CO₂ selectivity.?2?Benzene mainly decomposed to CO₂ and CO,but the sum of CO and CO₂ selectivity was only 56.5%.The concentrations of particles at the outlets of the DBD reactors were measured using SMPS.It found that ?-Al₂O₃ pellets and 5.0wt%CeO₂/?-Al₂O₃ pellets can effectively inhibit the exhaust of particles.?3?O₃ plays a key role in the benzene decomposition.It was found that O₃ can be decomposed into O₂2-and O₂-radicals on CeO₂ catalyst.MS singals of benzene or CO from the DBD reactor with 5.0wt%CeO₂/?-Al₂O₃ catalyst with or without discharge pre-treatments were also the same,this finding showed that O₂2-and O₂-free radicals formed from O₃ decomposition have no effect on benzene decomposition and CO oxidation in the absence of gaseous O₃.The decomposition mechanism of benzene may be promoted by O₃ decomposition into active oxygen caused.?4?The aged CeO₂/?-Al₂O₃ catalyst can be regenerated to its original catalytic ability.?5?Benzene removal rates in the DBD reactors with noble metal catalysts were significantly increased in comparison with the DBD reactor without a catalyst;at a fixed reaction temperature of 25? and SED of 400 J/L,the Au/?-Al₂O₃ catalyst has the highest benzene removal rate;when using the same noble catalyst loadings and at the same reaction temperature,the benzene removal rates increased with the increase in the energy density;when using the same noble catalyst loadings and certain energy density,benzene removal rates increased with the increase in reaction temperature.