Mechanism Research On Degradation Of Formaldehyde By Pulse Discharge Combined With MnO₂ Catalyst

With the development of society and economy, as the representative of the interior VOCs(Volatile Origanic Compounds),the formaldehyde is becoming more and more serious for people on the quality of life and physical health effects. Low temperature plasma combined with catalyst is the most promising new technology of VOCs degradation. But the inherent mechanism of the mutual coordination on the low temperature plasma and catalyst are still in the primary stage currently, need further study.This paper adopts a multi needle to plate reactor as pulsed discharge plasma, and make the formaldehyde as the research target pollutant, The change trend of degradation rate of formaldehyde and products have been conducted in pulsed discaharge, pulsed discharge combined with Mn O2 catalyst and pulsed discharge combined with Mn O2 catalyst modified by rare earth La Separately through machine rational experiments. The synergetic mechanism of pulse discharge Combined with catalyst has been furtherly analyzing on the basis of experiments through the establishment of mathematical model. The reaction dynamics simulation of pulsed discharge and pulsed discharge combined with Mn O2 catalyst for formaldehyde degradation have been conducted, the results of the study are as follows:Experimental results show that, when adopted single pulse discharge, formaldehyde degradation rate and product(O3, CO and CO2) concentration increases with the increase of pulse voltage, the selectivity to CO2 is low, when the pulse voltage is 23 k V, pulse frequency is 30 Hz, the degradation rate of formaldehyde is 81%, the concentration of O3 is 280.3ppm, and the selective of CO2 is 25%; when adopted the pulsed discharge combined with Mn O2 catalyst, the degradation rate of formaldehyde increased significantly, the concentration of O3 decreased significantly, and the selectivity of CO2 increased, when the pulse voltage is 23 k V, 8% loading amount of Mn O2 catalyst introduced in degradation of formaldehyde,the rate reached 92.1%, the concentration of O3 is 130.8ppm, and the selectivity of CO2 reached 58.8%; when adopted pulsed discharge combined with Mn O2 catalyst modified by rare earth La, the degradation rate of formaldehyde, O3 decomposition and the selectivity of CO2 was further improved, when the loading amount of La was 1%, 8% of Mn O2 catalyst performanced best, pulse discharge was 23 k V, formaldehyde degradation rate reached 98.5%, the selectivity of CO2 reached 64.5%, the concentration of O3 declined to 93.9ppm.Reaction kinetics simulation results shows that, the calculating concentration order of first radical is O>OH>H>N, the initial concentration of free radicals have direct proportion to pulse voltage. The component content of stimulant gas has certain effects on free radicals, the O and OH radicals concentration increases linearly along with the increase of oxygen and water vapor content, it is beneficial to the degradation of formaldehyde, but ozone utilization rate is not high. Under the direction of existing Mn O2 catalyst, the Mn3+ in the Mn O2 catalyst prompted O3 generating by pulsed discharge decomposition into active oxygen atom, and active oxygen atom increased the rate of formaldehyde degradation and the selectivity of CO2. The modification of rare earth La promoted the decomposition of ozone in the Mn O2 catalyst, generated more active oxygen atoms, and further improved the degradation rate of formaldehyde and the selectivity of CO2.Through the research on the mechanism of formaldehyde degradation by pulse discharge combined with Mn O2 catalyst, provides certain theory reference for waste gas degradation by pulse discharge combined with catalysts.