Low Temperature Catalytic Combustion Of Chlorobenzene Over Cr₂O₃ Based Composite Porous Catalysts

Chlorobenzene?CB?is a typical representative of chlorine-containing volatile organic compounds.Catalytic combustion is an efficient method for the treatment of CVOCs,and it is a hot research topic in the catalytic oxidation and removal of chlorobenzene.Increasing the chlorine resistance of catalyst materials is the key to developing high-performance catalytic combustion to treat CVOCs.The regulation mechanism in this aspect mainly has two kinds of synergy effects and structural effects.In this paper,the synergistic effect between Cr and Ti is used to improve the redox ability of the catalyst itself.In combination with the work of the research group on the pore structure or morphology of composite metal oxides in recent years,a specific microsphere shape and uniform composite are prepared.The Cr/Ti O_xcomposite oxide catalyst material is dedicated to increasing the exposure of the catalyst surface active sites and adsorption sites,which is more favorable for the adsorption and diffusion of reactants and product molecules.Combining the above two activity regulation mechanisms,the activity of the catalyst is more excellent,and the work of greatly improving the activity of the catalyst with reference to the"Sn doping effect"is carried out,and the performance of the Sn/Cr₂O₃based catalyst for degrading chlorobenzene is explored.Therefore,the research goal of this thesis is to prepare a porous composite metal oxide catalyst with uniform distribution of bulk phase and specific morphology,which can effectively inhibit aggregation and maintain catalytic combustion and degrade chlorobenzene,and provide a high-efficiency CVOCs catalytic degradation system.Important scientific basis.The main research contents and results of this thesis are as follows:The Cr/Ti O₂composite porous metal oxide catalysts with different morphologies were synthesized by hydrothermal method,coprecipitation method and impregnation method.The catalysts were characterized by XRD,SEM,TEM,BET,XPS and TPSR-MS.Characterization was carried out using chlorobenzene as a model reactant and the catalyst was evaluated in a fixed bed reactor.The Cr/Ti O₂composite porous metal oxide catalysts synthesized by the three methods have better catalytic activity than pure chromium and pure titanium in the catalytic combustion of chlorobenzene.The hydrothermal synthesis of h-Cr Ti0.4 sample is more active than the co-precipitation method and the impregnation method.The chlorobenzene conversion rate is 90%and the temperature is 246.23°C(impregnation method:T₉₀=300.18°C,coprecipitation method:T₉₀=282.93°C).The morphology of the sample prepared by hydrothermal method is solid microspheres,and the components are uniformly dispersed.The sample prepared by the impregnation method can obviously observe the Cr O_xirregular cube on the surface of the material,which belongs to the dispersive and uneven structure.The sample prepared by the coprecipitation method is the random block-like particles aggregate,the morphology is irregular,the composition is unevenly distributed,and the crystallinity is poor.The clear lattice fringes of the HRTEM image confirmed that the Ti O₂nanocrystals in close contact with the Cr₂O₃nanocrystals formed a Cr Ti O_xsolid solution structure due to the similar lattice spacing in the hydrothermally synthesized samples.In addition,the dechlorination ability of the samples synthesized by hydrothermal method and impregnation method was also investigated,and the changes of Cl species in the catalytic combustion process were studied by TPSR-MS monitoring technology.Compared with the sample synthesized by the impregnation method,the hydrothermally synthesized sample has a uniform mesoporous structure,which is beneficial to the desorption of Cl species from the catalyst surface,and the uniformly dispersed Cr Ti O_xsolid solution structure increases the valence state of the Cr species and makes the dispersion more uniform.The surface adsorption oxygen increased,and DCB was not detected in the samples synthesized by the two methods,indicating that the Cr/Ti O₂catalyst has ultra-efficient catalytic activity and can rapidly degrade the generated DCB.The porous structure is beneficial to the catalyst to better absorb and diffuse chlorobenzene and its intermediates,especially Cl species.In comparison,hydrothermal synthesis of samples has high degradation rate,lower Ea value and better stability.The Cr/Ti O₂microsphere porous catalysts with different Cr contents were prepared by hydrothermal method.The catalytic performance of the catalyst for the oxidation of chlorobenzene was investigated.The sample with h-Cr Ti0.4 ratio has the best activity.On the basis of T₉₀,the order of activity of porous microspheres synthesized by hydrothermal method is:h-Cr Ti0.4?246.23°C?>h-Cr Ti0.3?265.11°C?>h-Cr Ti0.5?276.97°C?>h-Cr Ti0.2?286.42°C?,indicating the best chromium loading.Compared with pure chromium and pure titanium samples,the h-Cr Ti series samples are more conducive to the catalytic combustion of chlorobenzene due to the strong interaction between Cr O_xand Ti O₂.Both are formed due to similar lattice spacing and similar ionic radii.Uniformly distributed Cr Ti O_xsolid solution microspheres,the size of porous microspheres is significantly smaller,the mesoporous distribution is more uniform,and the BET surface area is also significantly increased,which promotes the uniform distribution of Cr Ti species and increases the number of oxygen and oxygen vacancies on the surface.A series of"Sn-doped"Cr/KIT-6 porous catalysts were prepared by equal volume impregnation method.The degradation properties of the catalysts on chlorobenzene were investigated.The experimental results confirmed that the activity of the catalyst was significantly improved after the addition of Sn.The ordered three-dimensional mesoporous structure of the carrier KIT-6 was more favorable for the dispersion of the active components and the adsorption and desorption of the reactants and products.When the molar ratio of doping is Sn/?Cr+Si?=0.1,Cr/Si=1:3,the activity is optimal,and T₉₀is242.45 ?.