Toluene Removal By Adsorption And Non-thermal Plasma:Catalyst Preparation And Performance Study

Volatile organic compounds?VOCs?are important precursors for the formation of secondary pollutants such as fine particulate matter PM_2.5.5 and ozone?O₃?,which in turn cause atmospheric environmental problems such as smog and photochemical smog.Adsorption-Non-thermal plasma catalysis technology can effectively degrade VOCs,and the introduced catalyst plays an important role in improving the degradation rate of VOCs,the selectivity of CO₂,and the decomposition of by-product O₃.Therefore,it is very necessary to further study the preparation of the catalyst,the plasma synergistic oxidation performance and the stability.In order to solve the problem of how to select catalysts in the treatment of VOCs,this study used ZSM-5 molecular sieves,dielectric materials TiO₂ or a mixture of both as carriers and Mn-Ag as active components to prepare catalysts.Firstly,the effects of different carriers on the adsorption performance of toluene and the oxidation performance of non-thermal plasma were investigated,and the optimal carrier was selected.Then the effect of preparation methods of the catalyst,the loading position and total amount of the active component on adsorption of toluene,degradation effect and by-products were studied,and a catalyst with good adsorption performance and plasma oxidation performance was prepared.Finally,the stability of the catalyst was studied after multiple adsorption-non-thermal plasma discharges.The main conclusions of the paper are as follows:?1?The adsorption performance of toluene for different carriers varied from large to small:ZSM-5>mixed filler>TiO₂.The main reason was that the specific surface area of TiO₂ was 30m²/g,which was much smaller than the specific surface area of 248m²/g of ZSM-5.The toluene degradation effect of the mixed filler was obviously better than that of the ZSM-5.The main reason was that the addition of TiO₂ enhanced the discharge effect of the mixed filler,thereby more active particles to participated in the toluene oxidation process.The results of mixing ZSM-5 with TiO₂ at different mass ratios showed that when the mass ratio was 1:1,both the adsorption effect and the non-thermal plasma degradation performance were good.?2?Catalyst M1 was prepared by impregnating Mn-Ag on the surface of ZSM-5and then mixed with TiO₂.Mn-Ag/TiO₂ were prepared by sol-gel method,and then mixed with ZSM-5 to prepare catalyst M2.The mass ratio of ZSM-5 to TiO₂ for M1and M2 was 1:1,and the Mn and Ag contents were both 5%.The results of applying M1and M2 to the adsorption-Non-thermal plasma system showed that:M2 not only adsorbed 72 mg/m³ of toluene,but also more than 44 mg/m³ of M1.It was also superior to M1 in non-thermal plasma synergistic catalytic oxidation of toluene.And the production of by-products O₃ and N₂O was also less.?3?In order to further optimize the M2 catalyst,the influence of Mn-Ag loading on the adsorption-non-thermal plasma degradation was studied.The results showed that when the loading was within a certain range,the saturated adsorption capacity of M2catalyst increased with the increase of loading,but during the degradation of adsorbed toluene,when the loading of Mn-Ag was 5.0wt.%,CO_x concentration and CO₂selectivity were highest,and relatively low concentration by-products were produced.?4?After 10 successive adsorption-discharge cycles,the M2 catalyst with 5%Mn-Ag loading still maintained good adsorption capacity and the regeneration rate was as high as 69%.However,as the number of discharges increased,he catalytic oxidation effect of the adsorbed toluene and by-product suppression effect gradually decreased.By analyzing the physical and chemical properties of the catalyst surface and the ability to degrade toluene before and after discharge treatment,it was found that:after repeated adsorption-non-thermal plasma degradation,the surface and lattice structure of the catalyst remained intact,and the accumulation of organic by-products and carbon deposition on the catalyst surface the main reasons for the degradation of the catalyst adsorption performance and plasma oxidation performance.