The Removal Of Toluene In Flue Gas Using Low-Temperature Plasma Associated With Catalysts

Recently,with the development of the industrialization process,the massive emission of Volatile Organic Compounds(VOCs)pollution in our society causes a serious damage to the environment and simultaneous pose a threat to human health.Searching for an effective and economical method to reduce the content of VOCs is one of the hotspots in catalytic research.Among them,the combination of non-thermal plasma and catalysts to treat the VOCs flue gas is a technology with great potential,in which plasma is used to generate high-energy active species to promote the catalytic reaction.The comnination technology takes the advantages of plasma with rapid reaction rate and mild reaction conditions associate the features of catalysts i.e.high catalytic degradation selectivity thus present a promising applications for eliminating VOCs in industrial flue gas.However,currently,investigations of non-thermal plasma-catalysis mainly focused on the influence of non-thermal plasma but not the catalysts in the entire system due to the complexity of the non-thermal plasma reaction system.In application counterpart,toluene,a representative substance of monocyclic organic compounds,is widely used in various fields of chemical process thus a common and typical VOCs in reality.Therefore,in this thesis,toluene is used as the model molecular to study the effect of the catalyst under low energy density plasma.Also the catalytic reaction mechanism during the plasma reaction is investigated and proposed.The works of this thesis includes:Firstly,a strategy which weakening the effect of plasma and then highlighting the influence of the catalyst is proposed to study.In this thesis,the effects of plasma generated by DBD on the conversion rate and energy consumption of toluene under different power,different carrier gas and different catalyst supports are firstly investigated.The results indicate that the air as carrier gas has the lowest breakdown voltage and highest selectivity to other gases e.g.oxygen,nitrogen,argon,helium gases.Without the assisted of catalyst support amd used air as the carrier gas,no catalytic degradation of toluene was detected under 27 W(30V,0.9A)plasma condition.Among 13X,Al2O3,TiO2,and ZrO2 catalyst supports as the filling media,the experimental results indicated that 13X shows the highest catalytic degradation performance owing to the larger specific surface area and the appropriate dielectriche to the plasma-catalytic(one-pot)system.Therefore,the plasma conditions(30V,0.9A),the carrier gas(air)and the catalyst support(13X)are chosen to as the basis for the following studies.Secondly,the influence of the Cerium loading on the 13X toward the catalytic activity was further investigated and the role of ozone in the reaction process is explored.The results show that the conversion of toluene and the selectivity of carbon dioxide are the highest when the Ce loading is 30%;ad the catalyst is much stable when the Ce loading is 10%;while the CO2 selectivity is relatively high when the Ce loading is 40%.Combined with the catalytic degradation activity and the characterization results of BET,XPS,H2-TPR,SEM,etc.,a possible catalytic reaction mechanisms was proposed for the non-thermal plasma-catalysis as follows.Benefiting from the larger surface area of 13X,the toluene can easier adsorb on the catalyst.After being activated by plasma,the toluene species desorb from 13X will react with species such as reactive oxygen species produced by nearby Ce3+ species and become CO2 and H2O.Among them,the reaction of Ce3+ species under the action of plasma facilitates the generation of reactive oxygen species.Finally,a dual-metal oxide Mn-Ce catalyst is prepared using a stepwise impregnation method in order to study the performance of the bimetallic catalysts.The experimental results exhibit that the 10%Ce-20%Mn/13X catalyst shows higher catalytic activity than the 10%Ce/13X catalyst,and the toluene removal rate reached to 73.3%.It can be concluded that the introduction of Mn can effectively increase the oxidation activity of the Ce-based catalyst.Based on this study of Ce-based catalysts,this thesis carry out a preliminary economic analysis of the plasma-catalysis treatment ofVOCs.