Preparation And Modification Of Supported Chromium Cerium Oxide Catalyst And Catalytic Performance For CVOCs Oxidation

Chlorine-containing volatile organic pollutants（CVOCs）can stay in the natural environment for a long time due to their high toxicity,high stability,and difficulty in degradation,causing persistent harm to the environment and human health.With a wide range of industrial applications,CVOCs account for a large proportion of harmful air pollutants.Among the many current CVOCs treatment technologies,the catalytic oxidation method has the advantages of low treatment temperature,low energy consumption and good elimination effect,and is considered to be the most economical and efficient method.In this paper,mixed oxides Cr₂O₃and Ce O₂are used as active component substrates,Al₂O₃,cordierite and ZSM-5are used as carriers,and supported Cr-Ce-O catalysts are prepared by citric acid complexation.The molar ratio and transition of Cr/Ce are explored.The effect of metal oxide doping,carrier,doping amount and calcination temperature was detected on the performance of chlorobenzene oxidation.The effects of different reaction conditions including water vapor,space velocity,concentration of chlorobenzene and mixed components on the catalytic oxidation performance of chlorobenzene and the toxicity evaluation including the relationship between the concentration of Cl₂in the exhaust gas and the reaction temperature and time and the anti-chlorine poisoning performance of the catalyst were also studied.The physical and chemical properties of the prepared catalyst were characterized by XRD,BET,XPS,H₂-TPR,SEM and other analytical methods,and the following conclusions were obtained:（1）The conversion rate of chlorobenzene is the highest when the molar ratio of Cr/Ce is1:2.Catalysts with different Cr/Ce moles have different surface structure characteristics in the same catalyst carrier Al₂O₃.The oxidation characteristics of the catalyst are related to the pore volume and average pore diameter.The oxidation activity of different transition metals is specifically expressed as Zr O₂>Ni O>Mn O_x>Co₂O₃>Fe O_x>Cu O.Among them,the Cr-Ce-O/cordierite catalyst doped with Zr O₂performed best,reaching 91.5%.The interaction between Cr₂O₃and Zr O₂promotes the improvement of the oxidation-reduction capacity of the catalyst,which is beneficial to the performance of the oxidation activity of the catalyst.The Cr₂O₃-Ce O₂catalyst with cordierite as the carrier has the best oxidation activity,and the 24h stability test shows that the conversion rate of the catalyst for catalytic oxidation of chlorobenzene is always maintained at 99.0%.In addition,different calcination temperatures will significantly affect the surface structure and pore structure of the catalyst.（2）The doping amount of transition metal has a great influence on the oxidation activity of the catalyst.The catalyst doped with Zr O₂exhibits a lower reduction temperature and a larger H₂reduction peak area,thereby forming a combined reduction peak.The oxidation activity of the catalyst is the highest when the Zr/Cr molar ratio is 0.50 and 0.75.And with the increase of the doping amount of Zr O₂,the characteristic peak of Ce³⁺shifts to low binding energy.The increase of oxygen vacancies promotes the increase of surface-active oxygen,which is beneficial to the improvement of the catalytic oxidation performance of the catalyst.（3）The competitive adsorption of water vapor on the surface-active position of catalyst will occur.When the space velocity is 7500·h^-1,a more ideal conversion rate of chlorobenzene can be achieved to a certain extent.As the concentration of chlorobenzene continues to increase,the catalytic conversion efficiency of chlorobenzene continues to decrease.When the molar of toluene and chlorobenzene is 2:1,the conversion rate of the two is the fastest.It shows that the two have a competitive effect on the active site,and the presence of toluene will inhibit the conversion of chlorobenzene to a certain extent.The degradation of nitrates will produce large amounts of harmful NO、NO₂and NO_x.With the increase of the reaction time,the Cl₂content in the tail gas of the catalyst gradually increased during the experiment.The amount of Cl₂produced by the catalyst supported by cordierite is higher than that of alumina and ZSM-5.Compared with the catalytic activity of the catalyst without pre-poisoning treatment,the catalyst of the poisoned experimental group had low conversion efficiency to chlorobenzene.The degree of poisoning of cordierite-supported catalyst is lighter than that of alumina.Comprehensive analysis of data shows that the poisoning is the most serious under the conditions of 20%HCl concentration and 4h stirring time.