Mechanism Of CO Oxidation In Air Dielectric Barrier Discharge Plasma

VOCs(Volatile Organic Compounds)come from a wide range of sources,are poisonous and volatile,and harm the atmospheric environment and human health.Therefore,it has become urgent to solve the environmental problems caused by VOCs.Plasma can oxidize volatile organic compounds at room temperature or even low temperature,which has the advantages of fast reaction rate and simultaneous oxidation of a variety of pollutants.Therefore,its application in the treatment of VOCs has attracted widespread attention in recent years.So far,although there have been a large number of reports on the oxidation of VOCs in plasma,most of the existing reports have explored the technical route of the application of plasma,and the understanding of the oxidation mechanism of VOCs in plasma is very limited.In view of this,this paper carried out the measurement of dielectric barrier discharge characteristics in air atmosphere,and further studied the gas phase oxidation process of CO in plasma under different experimental conditions by taking CO,the most basic VOCs reaction process,as the model molecule.The main results and conclusions are as follows:(1)Dielectric barrier discharge in simulated air atmosphere:peak voltage,gas temperature and relative humidity have little influence on the electrical characteristics of dielectric barrier discharge.At room temperature,with the increase of peak voltage,the discharge power increases,the concentration of O₃ decreases,and the concentration of NOx changes monotonically with the discharge power.At the same discharge power,with the increase of gas temperature(90?-190?),the discharge products in air atmosphere are mainly N₂O,NO,NO₂ and O₃.The concentration of N₂O decreases with the increase of gas temperature,the concentration of NO and NO₂ decreases first and then increases with the increase of gas temperature,and the concentration of O₃ decreases monotonically.NO and NO₂ will not be produced only by changing the relative humidity at room temperature,and the concentrations of N₂O and O₃ will decrease with the increase of relative humidity.(2)CO oxidation process in plasma:in the dry gas,changing the gas temperature has little effect on the CO oxidation process,and the CO conversion rate only increases from 4%to 6%in the temperature range,which indicates that the oxidizing products of the gas phase,such as NO,NO₂and O₃,do not contribute to CO oxidation,while the contribution of CO oxidation in the dry gas is more likely to come from the O atoms produced in the gas phase.In humidity,the increase of relative humidity can promote CO oxidation obviously.At 25?,with the relative humidity increasing from dry gas condition to 49%,the CO conversion rate increased from 15.1%to 49.3%.This is because OH radicals can be generated in wet gas discharge,and the rate constant of OH radical oxidation of CO reaction(CO+OH?CO₂+H)is several orders of magnitude higher than that of CO oxidation reaction(CO+O?CO₂)initiated by O atoms in the temperature range under investigation.In addition,the discharge results in the air plasma with CO₂ as the model molecule show that under different gas temperature,relative humidity and input power conditions,CO₂ cannot be decomposed to CO.This shows the oxidation of CO to CO₂ in the dielectric barrier discharge plasma in air atmosphere is unidirectional and the reverse reaction cannot occur.