Study On The Catalytic Oxidation Of Toluene And Acetone By Zirconium-modified Manganese And Cobalt Oxide

Volatile organic compounds(VOCs)are one of the major pollutants in the atmosphere,which are widely available,difficult to remove and prone to damage to the environment and humans.Catalytic oxidation is an effective technology for the treatment of VOCs,and the core of this technology is the development of catalysts.The synthesis of efficient catalysts for catalytic elimination of VOCs in the presence of water is a hot and difficult topic of research.The transition metal oxides such as MnOx and CoOx present problems of slow activation of oxygen,poor activity stability and water resistance.In order to solve these problems,this paper chooses to load various active transition metals with zirconium oxide as a support,as well as to use zirconium to modify manganese and cobalt oxides,and to catalyze the oxidation of toluene and acetone as a model reaction,to investigate the interactions between zirconium and other metals and their effects on catalytic performance by various characterization techniques.To explore means to promote the activation of oxygen in the gas phase.Catalysts loaded with different metal oxygen species(Ce,Mn,Cu and Co)on ZrO2 as a support were synthesized by impregnation and hydrothermal methods,and their differences in the oxidation of toluene were investigated.The physicochemical characterizations of the catalysts are performed by XRD,N2-adsorption desorption,H2-TPR,O2-TPD,and in situ DRIFTS.The results show that the metal-support interactions could improve the electron transfer ability and oxygen mobility of the catalysts.Among them,the MnOx/ZrO2 catalyst can remove toluene more effectively,reaching a conversion efficiency of 90%at 280℃.The increased activity is associated with more surface adsorption sites and higher oxygen mobility,meanwhile,the chemically stable ZrO2 can ensure a good catalyst lifetime.But the catalyst exhibits a high activity temperature.In order to improve the catalyst activity,a series of ZraMn1-aOx(a=0,0.2,0.4,0.6,1)catalysts were synthesized by solvothermal method.The test results show that the catalytic activity of Zr0.6Mn0.4Ox sample for the complete oxidation of toluene and acetone is significantly higher compared with MnOx catalyst,and the temperatures of 90%conversion(T90)of toluene and acetone are 269 and 214℃,respectively.Combined with the analysis of various characterization results,the introduction of Zr affects the physicochemical properties of the catalyst,including the oxygen vacancies,the valence of surface elements and the content of surface reactive oxygen species.Despite the T90 value is significantly lower,the activity of the catalyst is still not satisfactory compared to the previous literature.However,the catalyst is able to maintain high activity in the presence of water,suggesting that the zirconium modification effectively improved the water resistance of the catalyst.In order to synthesize catalysts with low temperature activity as well as high water resistance,a series of ZraCo1-aOx(a=0.2,0.3,0.4,0.6,0.8)catalysts were prepared by a hydrothermal method.A series of spherically structured ZraCo1-aOx catalysts with different molar ratio of Zr/Co exhibit much higher activity compare to Co3O4.Among these catalysts,The Zr0.4Co0.6Ox catalyst not only shows high catalytic activity for the oxidation of toluene(T90=231℃)and acetone(T90=208℃),but also maintained long-term activity stability.Moreover,the activity can be unaffected in conditions containing 3 vol%water vapor.The characterization results of XRD,N2-adsorption desorption,SEM,TEM,H2-TPR,O2-TPD,XPS and in situ DRIFTS characterization results of catalysts reveal Zr doping on the physicochemical properties of ZraCo1-aOx.The superior catalytic performance of the Zr0.4Co0.6Ox catalyst can be attributed to the large specific surface area,low temperature reduction and abundant surface adsorbed oxygen species,which are associated with the formation of Zr-O-Co bonds.In addition,the reaction process of toluene and acetone on the Zr0.4Co0.6Ox surface is also investigated,which confirmed that the reaction process of organic molecules on the catalyst surface followed the MvK mechanism.