Study On Benzene Degradation In A Packed-bed Discharge Reactor Filled With Mn-ce-loaded Micropore Materials

Volatile Organic Compounds（VOCs）would be a great threat to human health and ecological environment as the atmospheric pollutants.VOCs control technologies include non-thermal plasma technology,photocatalysis,combustion,biological and so on.Non-thermal plasma technology has the advantages of fast treatment and simple equipment for VOCs degradation,but it also has some disadvantages such as low energy yield and organic byproducts generation during VOCs degradation process.Microdischarge in small gaps has high electron density and active species,which is beneficial to VOCs treatment.In the paper,a kind of discharge device filled with porous materials with micron pore size was designed to generatre microdischarge for degradation of benzene.Active catalytic components were also loaded on porous materials to form micro-plasma catalysis for promoting the benzene degradation.The influences of electrode configuration,porous ceramic morphology,filling condition,and other factors on microdischarge characteristics and benzene degradation were explored.Moreover,the effects of supported Mn-Ce catalysts on the degradation efficiency,energy efficiency of benzene and the generation of byproducts were also studied.The specific research contents and results are as follows:（1）The factors of three-electrode structure improved microdischarges generation and benzene abatement were researched.The porous ceramic with pore size of 60μm was used as the dielectric.The three-electrode configuration produced more discharge area and filamentary pulse discharge channels than two-electrode configuration in the discharge gas gap under the same applied voltage.Moreover,the discharge power was increased from 0.8 W（two-electrode configuration）to 8.6 W（three-electrode configuration）and the benzene degradation efficiency was correspondingly increased by 35.1%.Compared to spring electrode,the mesh high-voltage electrode can enlarge the discharge area and intensity,and enhance the electric discharge power by 4 W,leading to higher benzene degradation efficiency.But the energy efficiency of spring electrode was little higher than the others.In addition,when the pore size of porous ceramic tube was 60μm,the stable microdischarge led to the higher benzene degradation efficiency and energy efficiency compared to that when pore size of ceramic tube was 200μm.（2）The structure of packing bed filled with porous ceramic particles affects the generation of microdischarge and benzene degradation.The three-electrode packed-bed DBD structure had higher benzene degradation efficiency,energy efficiency,and CO₂ selectivity than the two-elecrtrode packed-bed DBD structure in the same energy density.The effect of particle size on microdischarge generation and benzene decomposition was also studied.The filling length and particle size of porous materials affected the microdischarge characteristics and benzene degradation efficiency.The results show that the benzene degradation efficiency and energy efficiency were the maximum with the 5 cm filling length and the 0.18-0.25cm particle size.In addition,the gas flow rate and benzene initial concentration were both inversely proportional to the benzene degradation efficiency,and proportional to the energy efficiency.The gaseous by-products were measured by GC-MS.The by-products mainly included acids,ketones,alkanes as well as aldehydes.（3）The Mn-Ce loaded porous catalysts were used for benzene degradation.The Mn-Ce loaded porous catalysts were beneficial to benzene deposition,and manganese oxides and cerium oxides had synergistic effect on catalytic performance.Compared to other ratios of Mn and Ce,Mn:Ce（3:1）loaded porous catalysts had a higher activity in terms of benzene degradation efficiency,energy efficiency,and CO₂ selectivity.Furthermore,γ-Al₂O₃ can improve the catalytic activity.The physicochemical properties of different catalysts were characterized by X-ray diffraction（XRD）,Scanning Electron Microscopy（SEM）,and X-ray photoelectron spectra（XPS）.The results indicate there was remarkable interaction amongγ-Al₂O₃,Mn Ox,and Ce O₂ in the plasma-catalytic system.The surface adsorbed active oxygen ratio of Mn3Ce1/γ-Al₂O₃（79.16%）was higher than that of Mn3Ce1（63.21%）catalyst,and a higher content of active oxygen would efficiently improve the degradation of benzene.