Study On Degradation Performance And Mechanism Of Toluene By Low Temperature Plasma In Conjunction With Supported Photocatalyst

"Mutagenesis、carcinogenesis and teratoeenesis",photochemical smog,haze and other events caused by volatile organic pollutants（VOCs）have direct and indirect harm to human health and ecological environment.Therefore,it is of great significance to study high-efficiency,energy-saving and pollution-free VOCs treatment technology.As an emerging VOCs treatment technology,low-temperature plasma technology has advantages of simple operation,low reaction temperature and high removal efficiency compared with traditional treatment methods,so it has a good application prospect.In this study,the DBD plasma technology was used to study the effects of initial concentration,gas flow rate,discharge voltage,energy density（SED）and moisture content on toluene degradation effect and by-product generation were systematically discussed.The results showed that with the increase of initial concentration and gas flow rate,the degradation rate of toluene,the selectivity of CO₂and the concentration of NO₂ and O₃ all decrease,while the selectivity of CO increases on the contrary.With the increase of discharge voltage,the degradation rate of toluene and the concentration of by-product NO₂ increased,the selectivity of CO₂ increased first and then decreased,the selectivity of CO remained almost constant,and the concentration of by-product O₃ decreased.With the increase of energy density（SED）,the degradation rate of toluene,the selectivity of CO₂ and the by-product NO₂ all increased,while the selectivity of CO decreased,and the concentration of by-product O₃ first increased and then decreased.With the increase of water content,the degradation rate of toluene and the selectivity of CO₂ increased first and then decreased,while the selectivity of CO decreased,the concentration of by-product NO₂increased,and the concentration of O₃ decreased.At the same time,the relationship between energy efficiency and energy density in the low-temperature plasma unit was evaluated.The results showed that the energy efficiency of the low-temperature plasma unit was only 0.12-0.4 g·k Wh^-1,and the main energy loss was in the formation of by-products and the photothermal loss.Five supported photocatalysts,TiO₂/γ-Al₂O₃,Ce-TiO₂/γ-Al₂O₃,Ag-TiO₂/γ-Al₂O₃,La-TiO₂/γ-Al₂O₃,Co-TiO₂/γ-Al₂O₃,were prepared and characterized.A low-temperature plasma combined photocatalytic reactor was built to study the effects of different photocatalysts on the degradation rate of toluene,CO₂,CO selectivity,and by-product NO₂ and O₃ concentrations without Uv and additional Uv.The results show that without additional UV,the combination of plasma and photocatalyst can significantly improve the degradation rate of toluene and CO₂selectivity,reduce the selectivity of CO,and greatly reduce the generation of NO₂ and O₃.When Ag-TiO₂/γ-Al₂O₃ is used,the maximum degradation rate of toluene can reach 100%,the selectivity of CO₂ is 81%,and the formation of by-products is greatly inhibited.With the addition of extra UV,the presence of UV had little effect on the degradation rate of toluene,but could improve the selectivity of CO₂ and inhibit the concentrations of CO,NO₂ and O₃.The possible reason was that the light generated by the plasma is not enough to induce the occurrence of photocatalysis.Compared with the energy efficiency of the low-temperature plasma alone,the energy efficiency of the plasma-photocatalytic system is about 1.4-3 times higher,indicating that the low-temperature plasma and photocatalyst combined to decompose the same amount of toluene can save more energy.Finally,the intermediates of toluene degradation in different systems were analyzed by GC-MS,and the mechanism of toluene degradation by low-temperature plasma alone and low-temperature plasma-photocatalytic system was deduced.The results can provide a theoretical basis for the study of the performance of low-temperature plasma degradation of VOCs,and have a certain guiding significance for the study of the application and mechanism of low-temperature plasma degradation of VOCs.