Preparation Of Supported Copper-manganese-cerium Oxide Catalyst And Study Of Its Catalytic Performance On CVOC

Chlorinated volatile organic compounds（CVOCs）are one of the important components of volatile organic pollutants（VOCs）.They have received widespread attention due to their extensive sources,high toxicity,difficulty in being degraded by the natural environment and organisms,easy to produce high chloride by-products,and significant harm to human health.Currently,catalytic oxidation technology has become the mainstream technology and development direction in the field of CVOCs treatment due to its advantages such as low ignition temperature,low energy consumption,high removal rate,and no secondary pollution.The preparation of catalysts with high removal rate,strong stability,and low preparation cost is the core of catalytic oxidation technology.In this paper,supported catalysts were prepared using copper manganese cerium oxide as the active substrate.The effects of Mn/Cu molar ratio,Ce O₂loading method,doping amount of Cu,Mn,Ce oxides,calcination temperature,time,carrier type,and preparation method on the catalytic performance of the catalysts for the oxidation of chlorobenzene（CB）were studied.At the same time,the effects of different reaction conditions,including CB concentration,space velocity,water vapor content,and different levels of HCl poisoning in the system,on the catalytic oxidation of CB by the catalyst were investigated,and the mechanism of catalytic oxidation of CB by the catalyst was speculated.The physicochemical properties of the catalyst were characterized by XRD,SEM,BET,H₂-TPR,O₂-TPD,NH₃-TPD,XPS,in-situ DRIFT,and other analytical methods,and the following conclusions were obtained:（1）When the molar ratio of Mn/Cu is 5:2,the catalytic activity of 10 wt%Cu Mn O_x/20wt%Ce O₂/Cordierite catalyst is the highest.When the reaction temperature is 350℃,the CB conversion reaches 94.1%.The one-step supported catalyst exhibits higher oxidation activity compared to the distributed supported catalyst.The Cu Mn Ce O_x/Cordierite catalyst（Cu Mn O_xloaded at 20 wt%,Mn/Cu=5:2,Ce O₂loaded at 10 wt%）prepared by citric acid complexation method at 450℃for 4 h exhibits the best catalytic effect for CB,with a T₉₉of 300℃and excellent stability.Its surface structure is uniform and densely distributed spherical.The incorporation of Ce O₂in the one-step loading method is conducive to promoting the high dispersion of Cu Mn O_xcomponents and forming a Cu-Mn-Ce-O ternary solid solution.With the increase of Ce O₂loading from 10 wt%to 20 wt%,the H₂reduction peak amount of the catalyst increased from 1.99%to 4.32%,promoting the improvement of the oxidation and reduction ability of the catalyst.At the same time,the ratio of Ce⁴⁺/Ce increased from 75.7%to 81.4%,and the ratio of surface active oxygen(O_sur)/lattice oxygen(O_latt)increased from18.3%to 27.6%,indicating that the catalyst surface has more active oxygen.（2）The type and preparation method of catalyst carriers have important effects on their catalytic oxidation activity.Catalysts prepared with four types of carriers,different preparation methods,and complexing agents exhibit different surface structures.Among them,the Cu Mn Ce O_x/Cordierite catalyst prepared by citric acid complexation showed the best catalytic activity.Among the catalysts prepared with different supports and preparation methods,Cu Mn Ce O_x/ZSM-5 catalyst has the largest specific surface area and pore volume product,which are 160.0 m²/g and 0.221 cm³/g,respectively.Cu Mn Ce O_x/Cordierite catalyst exhibits the largest average pore size,which is 17.9 nm.Performance tests have shown that the catalytic activity of the catalyst is not related to its specific surface area and pore volume,but rather to its average pore size.The presence of a carrier during the reaction of the active component will affect the final reaction result of the active component,while whether the Mn oxide in the catalyst oxidation active component reacts with other active oxides will affect the oxidation activity of the catalyst itself.The more strong acid sites and the greater the amount of strong acid on the surface of the catalyst,the higher the catalytic oxidation activity.（3）Controlling the CB concentration at 250-500 ppm and the space velocity between5000-10000·h^-1can achieve an ideal CB catalytic effect.Adding 1%water vapor to the system can improve the ability of the catalyst to oxidize CB.At reaction temperatures of200℃and 250℃,the catalytic efficiency increases from 27.8%and 52.9%without adding water vapor to 34.8%and 64.9%,respectively.The catalyst pretreated with HCl at a concentration of 1%has a catalytic efficiency of 26.2%,51.9%,and 99.1%,respectively,at a reaction temperature of 200℃to 300℃.The oxidation activity of the catalyst is slightly lower than that of the untreated catalyst by 27.8%,52.9%,and 99.4%,showing good resistance to low concentrations of HCl.The main by-products of catalytic CB production are C₃H₇Cl and C₆H₁₄.It is speculated that the oxidation pathway of CB initially begins with dechlorination,decomposing aromatic hydrocarbons into phenolic species,and then converting them into cyclohexanone or benzoquinone species.Cyclohexanone or benzoquinone species are oxidized to maleic acid salt species.Some maleic acid salt species are oxidized to C₆H₁₄by active oxygen,and the other part combines with chemically adsorbed Cl ions to form C₃H₇Cl,which ultimately forms HCl,CO₂,and H₂O.