Study On The Activity Of Mn_yTi_1-yO_x Catalytic Oxidation Of Dichloromethane And Its Resistance To Chlorine Poisoning Under Microwave Field

Volatile organic compounds（VOCs）are important precursors of PM_2.5and O₃,posing a huge threat to the atmospheric environment and human health.Chlorinated volatile organic compounds（CVOCs）belong to a class of substances with high toxicity and difficult degradation of VOCs,and have a wide range of sources.Among many CVOCs treatment technologies,catalytic oxidation can realize the conversion of CVOCs at200～500°C and has high product selectivity,which can avoid the generation of dioxins.Therefore,it is considered to be one of the most effective and economic methods for treating CVOCs.Microwave,due to its unique micro heating characteristics,can enhance the degradation rate of VOCs in the low-temperature process during synergistic catalytic oxidation.However,catalyst poisoning and deactivation are inevitable in the process of CVOCs catalytic oxidation.Therefore,it is of great significance to clarify the mechanism of catalyst poisoning and deactivation,and develop a catalyst with high activity,high stability and suitable for CVOCs degradation under microwave field.This article takes dichloromethane（DCM）as the target pollutant and explores the degradation effect of DCM under microwave electromagnetic field and the catalytic characteristics of the catalyst.Firstly,using COMSOL simulation software,the optimal operating conditions for the device were determined to be the coupling arrangement of the magnetron tube and the catalyst placed on the top of the quartz tube.This condition is conducive to uniform distribution of electric field intensity and uniform heating of the catalyst.Subsequently,Mn O₂catalysts with rapid heating and high stable temperature were selected.Through conditional experiments,it was found that they can quickly and efficiently degrade DCM 12 minutes before the reaction,but the catalyst deactivation phenomenon is obvious in the later stage of the reaction.On the contrary,the Mn_yTi_1-yO_xtype M-T-1 catalyst doped with Ti element exhibits strong anti deactivation activity.The kinetic fitting results of the experimental data indicate that the process of microwave catalytic oxidation of DCM follows first-order reaction kinetics.Next,by changing the doping amount of Ti element in the catalyst Mn_yTi_1-yO_x,the M-T-3 catalyst with Mn:Ti=1:1 was determined to have the highest low-temperature catalytic activity,impact resistance,and deactivation resistance.The optimal reaction conditions for treating 1000ppm DCM with M-T-3 were determined using response surface methodology as follows:microwave power of 714 W,gas flow rate of 53 m L·min^-1.Under these conditions,the degradation rate of DCM can still reach over 95%after 60 minutes of reaction.After a 400minute activity comparison test,the promotion effect of microwave heating on catalyst activity and stability was clarified compared to conventional heating.By characterizing the physicochemical properties of the catalyst before and after the reaction,it was found that the deactivation of the catalyst was mainly related to catalyst coke deposition and chlorine poisoning.Based on mass spectrometry results,the possible reaction mechanism on the catalyst surface was inferred.This paper combines physical and chemical characterization methods with mass spectrometry analysis results to explore the reasons for the excellent low-temperature catalytic activity and stability of M-T-3 catalyst in microwave fields.The response surface methodology was used to determine the optimal process parameters for DCM degradation,revealing the poisoning mechanism of the catalyst,and speculating on the reaction mechanism of catalyst degradation of DCM in microwave fields,in order to provide reference for the practical engineering application of microwave catalytic oxidation technology in treating CVOCs.