Removal Of VOCs By Non-Thermal Plasma Combined With Manganese-Based Catalyst

Volatile organic compounds（VOCs）,as important precursors of PM2.5 and ozone,cause serious harm to human body and environment,and are highly concerned by society.Non-thermal plasma（NTP）exhibits good VOCs removal ability at normal temperature,and is easy to operate,and has received much attention in recent years.Non-thermal plasmas are often used in combination with catalysts to greatly improve the removal efficiency of VOCs and significantly improve CO₂conversion efficiency.Therefore,finding suitable catalyst-coupled plasma to remove VOCs has become a hot research topic.In this paper,refractory chlorobenzene and easily degradable ethyl acetate were used as target pollutants.The Non-thermal plasma（NTP）coupled manganese-based catalyst was used to investigate the discharge characteristics of Non-thermal plasma catalytic system and the low concentration of chlorobenzene and ethyl acetate.The degradation characteristics and the reaction mechanism of Non-thermal plasma catalytic degradation of VOCs were discussed.Firstly,two manganese-based catalysts,La Mn O₃and OMSs,were prepared by solid state method and sol-gel method.The physicochemical properties of XPS,XRD,BET,H₂-TPR,SEM and TEM were characterized.Secondly,the effects of different process parameters（initial concentration,residence time,catalyst placement,humidity）on the catalytic degradation efficiency and mineralization of chlorobenzene and ethyl acetate were investigated in a Non-thermal plasma reactor.The generation of ozone and NOx and the stability of the catalyst in a non-thermal plasma catalytic reaction system.Finally,the catalysts were characterized by FT-IR and BET,and the catalytic degradation mechanism of chlorobenzene and ethyl acetate was discussed.The main findings of the experiment are as follows:（1）La Mn O₃ and OMSs catalysts were prepared by sol-gel method and solid state method.The degradation performance of OMSs catalysts was better by the degradation experiments of chlorobenzene and ethyl acetate.At the same time,the introduction of OMSs catalysts also showed better selectivity for chlorobenzene and ethyl acetate CO₂.From the analysis of the characterization results,XPS characterization results show that the characteristic diffraction peaks of tetravalent manganese and lattice oxygen in OMSs catalysts are more obvious.The H₂-TPR characterization results show that the catalytic reduction temperature of the OMSs catalyst is lower,which confirms that the catalytic performance of the OMSs catalyst is stronger.（2）Under the conditions of Non-thermal plasma removal of chlorobenzene and ethyl acetate catalyst,the removal rates of chlorobenzene and ethyl acetate decreased with the increase of initial concentration under the conditions of Non-thermal plasma and low temperature plasma coupled catalyst.The amount of ozone generated and the amount of nitrogen oxides increase with the increase of the peak voltage.At the same time,the longer the residence time of chlorobenzene and ethyl acetate in the discharge zone,the higher the degradation efficiency,when the catalyst is placed at 0.2g.At the time,the low temperature plasma catalytic system achieves the best catalytic effect.The greater the humidity,the worse the degration of pollutants.（3）The stability of the OMSs catalyst in the NTP catalytic system was tested under voltage conditions of 3 k V and 5 k V,with voltage conditions alternating every 12hours.The OMSs catalyst in the chlorobenzene catalyst system maintained extremely high activity during the first voltage cycle.During the second voltage cycle,the catalytic activity decreased,and the chlorobenzene removal rate and CO₂ selectivity decreased.In the ethyl acetate catalyst system,the OMSs catalyst maintained extremely high catalytic activity during both voltage cycles.（4）The chlorobenzene catalyst system was analyzed.It was found that the intermediate by-products on the surface of the catalyst were benzene ring derivatives such as phenol and phthalic acid,as well as organic small molecules such as organic acids and alcohols.According to the analysis of intermediate by-products,chlorine was obtained.Benzene degradation can be divided into three pathways,the final products are CO₂,H₂O and HCl.The analysis of the ethyl acetate catalytic system revealed that the intermediate by-products on the surface of the catalyst were small molecules of alcohols,aldehydes,acids and alkanes,which were then reacted to form CO,CO₂ and H₂O.（5）The FT-IR and BET characterizations of the two catalysts were carried out.The characterization results showed that the structural properties of the catalysts did not change before and after the reaction.After a series of catalytic reactions,some by-products were deposited on the catalyst surface.The change of the catalyst after the reaction of the chlorobenzene catalytic system and the ethyl acetate catalytic system has changed,and the intermediate by-products produced by different catalysts under different catalytic systems are different.