Study On The Mechanism Of Catalytic Degradation Of Toluene By Continuous Discharge And Adsorptive Storage-discharge

Volatile organic compounds(Volatile Organic Compounds, VOCs) is one of the most important precursor of secondary pollution such as O3 and PM2.5. With the social development and economic development, VOCs emissions of china increased year after year, air pollution issue caused by the VOCs further highlight, control the pollution of VOCs pollution is imminent. Plasma-catalytic technology can degrade VOCs in ambient temperature and pressure, and the relate studies draw wide attention of scholars at home and abroad as a new air pollution purification technology with high conversion efficiency, fast response, reducing secondary pollution. Due to the complexity of the plasma-catalytic system, mechanisms about plasma-catalytic degradation of VOCs and the role of catalysts in the plasma degradation did not get an achievement as a result of lacking direct experimental evidence of the degradation, which impedes application of this technology.In this study, continuous discharge and adsorptive storage-discharge combined with γ-Al2O3, Ag/γ-Al2O3, NiO/γ-Al2O3 and MnOx/γ-Al2O3 for toluene adsorption and decomposition were investigated under ambient pressure and temperature to study the differences between two degradation methods and the adsorption of the catalyst and the role of the addition of active components during the toluene degradation. In addtion, a special plasma reactor was designed to study the adsorption species and intermediate products on catalysts surface during the toluene degradation in continuous discharge and adsorptive storage-discharge. At the same time, combined the GCMS results, the rate-determining step of toluene degradation pathway were discussed.Prepared Ag/γ-Al2O3, NiO/γ-Al2O3, MnOx/γ-Al2O3 by impregnation, the toluene degradation were MnOx/γ-Al2O3 > NiO/γ-Al2O3 > Ag/γ-Al2O3 > γ-Al2O3 >the blank pipe. The results show that the degradation of toluene in the plasma was influenced by the abilities of toluene adsorbed on the catalysts surface and decomposed of O3.The adsorptive storage-discharge method exhibited higher toluene conversion, CO2 selectivity and better carbon balance compared to the continuous discharge. In particular, the removal rate of toluene is 100%. By pre-adsorption of toluene greatly enhance the utilization efficiency of the active species generated in the plasma, intermittent discharge mode maintain the active sites of the catalyst exposed, thereby promoting the complete oxidation of toluene to CO2.The addition of active components can improved the toluene degradation. Loading of Ag can enhance the adsorption capacity of the catalyst due to form Ï€-Complexing bond. Surface electron affinity and the hydrogen sorption of γ-Al2O3 improved by loading NiO, and the stability of the benzene ring structure was weaken, which will reduce difficulty of chemical construction impacting to the methyl degradation. However, MnOx can hoist the redox properties of catalyst and enhance the capacity of the ozone degradation of the catalyst, thereby strengthen the activity of degrade toluene.Main intermediates of plasma catalytic degradation of toluene are benzyl alcohol, benzaldehyde, benzoic acid, esters and amine. The reaction process of plasma catalytic degrade toluene is speculated by GC-MS and in situ infrared spectroscopic, discharge patterns affect the degradation pathway of toluene. Intermediate products of adsorptive storage-discharge are less than the continuous discharge and the degradation of toluene is more thorough without formation of amines. Toluene â†' benzylalcohol â†' benzaldehyde â†'benzoic acid â†'small alcohols, acids, amines molecules â†' CO2 and H2 O is the main path of the degradation of toluene.