Experimental Study On Surface Dielectric Barrier Discharge Non-thermal Plasma Combined With ?-MnO₂ For The Degradation Of Low-concentration Toluene

In recent years,the emission of volatile organic compounds?VOCs?from the industrial sources increased gradually,which made serious environmental problems.The non-thermal plasma?NTP?technology,a new technology,had attracted significant attention.However,high plasma energy consumption and by-products have significantly limited its industrial applications.In this thesis,the homemade surface dielectric barrier discharge reactor coupled with the ?-,?-,?-,?-MnO₂ and the a-MnO₂/anatase TiO₂ composite catalysts were employed to study the interplay and synergistic action between the non-thermal plasma and the catalysts,in which the toluene,a typical VOCs,was used as the target pollutant.Firstly,the discharge characteristics and toluene degradation performance of the homemade surface dielectric barrier discharge were studied.The research results showed that with the action of the high voltage pulse power supply,the voltage of the surface dielectric barrier discharge was single pulse wave.With the increase of the specific input energy?SIE?,the toluene removal efficiency,the production and the escape of O3,the production of NOx,the COx yield,the CO selectivity and CO₂ selectivity increased gradually.Based on the analyses of the organic by-products,the pathways and the mechanism of toluene destruction were proposed as follows.The degradation was drivin by the high-energy electron,active radicals and O3 in the non-thermal plasma.Secondly,the ?-,?-,?-and ?-MnO₂ catalysts were synthesized by using a one-step hydrothermal method and their catalytic performances of toluene in the non-thermal plasma-catalytic process were evaluated.The research results showed that the ?-MnO₂ had shown the best activity among the investigated catalysts,which raised the toluene conversion from the 32.5%with the non-thermal plasma alone to 78.1%at the SIE of 160 J/L.The introduction of the catalysts could significantly improve the COx yield and reduce the escape of O3,the production of NOx and the types and the amounts of the organic by-products.Based on the analyses above,the pathways and the mechanism of toluene destruction in the non-thermal plasma-catalytic process were proposed.The excellent catalytic performance of ?-MnO₂ could be attributed to the double tunneled structure,the lowest Mn-0 bond intension,the best stability of the crystal in the non-thermal plasma and so on.Finally,the composite catalysts were prepared by the combination of the ?-MnO₂ and TiO₂ and their catalytic performances of toluene in the non-thermal plasma-catalytic process were evaluated.The effect of the types of the TiO₂,the preparation method and the composite ratio were investigated and optimized.The research results showed that the anatase TiO₂ is better than P25 and the composite catalyst prepared by in situ method is better than solid mixed method.The 0.2?-MnO₂/anatase TiO₂ presented the best activity,which raised the toluene conversion to 90.2%at the SIE of 178 J/L.The introduction of the composite catalysts could reduce the escape of O3 and the types and the amounts of the organic by-products.The characterization results showed that the specific surface areas and acid content of the composite catalysts were larger than single ?-MnO₂,which would benefit for the adsorption of the toluene and organic by-products so as to improve the removal efficiency of toluene.Besides,the composite catalysts could take advantage of the ultraviolet radiation in the non-thermal plasma-catalytic system to photocatalytic degradation the low-concentration toluene and organic by-products,which in turn would further enhance the removal efficiency of toluene.