The Study On Catalytic Oxidation Of Chlorinated Volatile Organic Compounds Over Composite Oxides

Chlorinated volatile organic compounds(CVOCs)have been widely applied in modern chemical industry.The emission of CVOCs have brought significant pressures on air environment and human health due to the chemical stability of such compounds.Dichloromethane(DCM)is one of the representative CVOCs,which has been widely used as a lipophilic solvent in the industries of paint,pharmacy,food,textile and rubber.However,the emission of dichloromethane in the atmosphere causes photochemical smog,damaging of zone layer and various human diseases.Therefore,dichloromethane is the key monitoring object in the air pollution control and much attention has been paid on the abatement.Compared to other methods,catalytic combustion is regarded as a promising way due to the advantages such as low elimination temperature,less energy consumption,simple treatment process,high elimination rate,no restriction of CVOCs concentration and no secondary pollution.Chromium-containing spinel oxides are highly active,highly selective and highly stable catalysts for the catalytic combustion of dichloromethane.Our previous works on this system pointed out that the excellent performance of such oxides lies in the good reducibility and high surface acidity of the oxide,which synergistically contribute in the observed high activity.In addition,the confinement of Cr species in the spinel structure prevents the possible loss of Cr during the reaction and thus avoids catalyst deactivation.In the current thesis,further investigations were conducted on mixed oxides,which include:1,The effect of B site cations on the properties of spinel oxides(AB2O4)and related catalytic behaviors for dichloromethane oxidation;2,The size effect of spinel oxides on the properties of the oxides and their catalytic behaviors in dichloromethane oxidation;3,Characterizations and catalytic performance of Cr-containing cmoposites with corundum-type structures.The results obtained in the current thesis are helpful for the the better understanding of the catalytic oxidation of CVOCs over composite oxide catalysts,and they provide useful information on the development of highly efficient catalyst systems.The specific research results of this thesis are as follows:1.Preparing a series of Zn-containing spinel ZnM2O4(M=Cr,Al,Fe)catalysts by sol-gel method,and the catalytic activity of the catalysts for dichloromethane oxidation was investigated:The result of the activity test showed that the ZnCr2O4 spinel catalyst has the best catalytic activity to dichloromethane,and can completely oxidize and decompose dichloromethane at 350 ?.The T50(temperature at 50%conversion)was 277 0C.Characterization results showed that the performance of the catalyst by the synergistic effect of surface acidity and redox.The ZnCr2O4 spinel catalyst had the surface acidity of the moderate acid strength and the best low temperature reduction performance,so the reaction performance was the best.2.The three-dimensional mesoporous silica material TUD-1 was synthesized by hydrothermal method,and different contents of x CoCr2O4(x = 5%,10%,20%,30%and 50%)on the silicon material TUD-1,the tested for catalytic combustion of dichloromethane was investigated.Explored the relationship between the intrinsic activity of the catalyst and the reducibility and surface acidity as well as the influence of CoCr2O4 particle size on the properties of the composite oxide and the related catalytic behavior.The results showed that 5 CoCr2O4/TUD-1 has high surface acidity and high surface Cr6+ ion density,so the catalyst had a higher intrinsic activity.3.Using citric acid as complexing agent and nitrate as precursors,the corundum-type structural compound Cr1.3Fe0.7O3 was prepared by sol-gel method in different calcination temperatures and explored the catalytic combustion performance of dichloromethane.The results showed that the catalyst calcined at 400 ? have the best catalytic activity,but without a complete corundum crystal.Characterization results showed that calcined catalysts above 500 ? can form a complete pure corundum-type crystal.In addition,the temperature affected the catalyst particle size and surface elemental composition,especially the surface Cr species content,thereby further affecting the catalytic activity of the catalyst.Among the prepared catalysts,the high surface area(169,4 m2·g-1)of the Cr1.3Fe0.7O3-4 oxide calcined at low temperature gived it the highest surface acid amount and the best reducibility,and thus had the best catalytic activity.