The Destruction Of VOCs Over Fe-Mn/Al₂O₃ Catalyst In A Non-thermal Plasma-catalysis Reactor

Volatile organic compounds（VOCs）,especially aromatic VOCs with higher toxicity（such as benzene,toluene,ethylbenzene and chlorobenzene）,are coupled with other air pollutants to form secondary aerosols and ozone,which can easily cause air pollution problems such as haze,greenhouse effect,photochemical smog and ozone layer destruction,and harm to ecological safety and human health.Non-thermal plasma coupled with catalytic technology combines the advantages of non-thermal plasma technology and catalytic oxidation technology with lower energy consumption,higher energy utilization,high selectivity and high removal efficiency,which has a wide application prospect in the field of VOCs harmless treatment.In this paper,a series of Fe_xMn_y/Al₂O₃ catalysts were prepared by reflux-coprecipitation method.The catalysts were characterized by BET,XRD,XPS,SEM and TEM,and then the destruction of toluene and chlorobenzene over Fe_xMn_y/Al₂O₃catalyst in a non-thermal plasma-catalytic reactor were studied.Meanwhile,the effects of initial concentration,humidity and residence time of toluene/chlorobenzene on the removal efficency and secondary pollutants were investigated.Compared with the non-thermal plasma,the removal efficiency of toluene and chlorobenzene was significantly increased and the secondary pollutants such as O₃ and NO_x were significantly reduced in a non-thermal plasma-catalytic reactor packed with Fe_xMn_y/Al₂O₃catalyst.Under condition of the specific energy density of 1500 J/L and the space velocity ratio of 80000 m L/（g·h）,Fe₁Mn₁/Al₂O₃ exhibited better removal efficiency（98.59%）and CO₂ selectivity（88.02%）for toluene;similarly,Fe₁Mn₁/Al₂O₃ exhibited better removal efficiency（95.77%）and CO₂ selectivity（93.11%）for chlorobenzene under condition of the specific energy density of 1800 J/L and the space velocity ratio of 80000 m L/（g·h）.In order to obtain the effect of the competition between toluene and chlorobenzene in a non-thermal plasma-catalytic reactor,the catalytic degradation of a mixture of toluene and chlorobenzene over Fe₁Mn₁/Al₂O₃catalyst in a non-thermal plasma-catalytic reactor were also studied,and the effects of toluene/chlorobenzene ratio,initial concentration and residence time on the removal efficiency of toluene and chlorobenzene and the formation of secondary pollutants were also discussed.Under the conditions of toluene/chlorobenzene of 3:1,specific energy density of 1800 J/L and space velocity ratio of80000 m L/（g·h）,the removal efficiency of toluene,chlorobenzene and CO₂ were in sequence as 92.57%,85.71%and 81.23%,which was slightly lower than that of individual component of toluene or chlorobenzene in a non-thermal plasma-catalytic reactor packed with Fe₁Mn₁/Al₂O₃catalyst.There was competition adsorption between toluene and chlorobenzene on the surface of the catalyst,and chlorobenzene inhibited the toluene degradation.The increase of chlorobenzene content led to the production of the chlorine containing by-products.The by-products adsorbed on the catalyst surface occupied part of the active sites,which inhibited the interaction between plasma and catalyst,resulting in the reduction of catalytic performance and increasing the production of O₃,NO_x and other by-products.The kinetic analysis results showed that the reaction rate constant of toluene/chlorobenzene mixture was lower than that of individual component of toluene/chlorobenzene,proved that there was mutual inhibition between toluene and chlorobenzene.The activation energy for simultaneous degradation of toluene and chlorobenzene was also less than that of individual component of toluene/chlorobenzene,indicating that more ozone was participated in the reaction and reducing the activation energy of toluene/chlorobenzene oxidation.