Construction Of Ce-based Ordered Mesoporous Catalyst And Its Catalytic Activity And Stability For CVOCs Elimination

Chlorinated volatile organic compounds（CVOCs）are widely distributed in the environment due to their solubility and the particularity of chlorinated structural units.CVOCs has enormous damage to the environment and human health,which would give rise to the greenhouse effect and biological canceration because of its high toxicity and slow natural degradation.Catalytic combustion is considered to be one of the most effective methods to eliminate CVOCs emissions due to its advantages of low energy consumption,high removal rate and low secondary pollution.CeO₂ has high oxygen storage/release capacity and abundant oxygen vacancies,so it is considered as a promising catalytic oxidation material.Due to the adsorption of Cl^-on the active sites,pure cerium oxide is easy to inactivate.However,the defects and oxygen vacancies in mixed metal oxide catalysts can remove chlorides and resist chlorine poisoning deactivation.Because of its outstanding heat resistance and anti-poisoning properties,TiO₂ is widely used in catalytic reactions.In the composite catalyst,CeO₂ provides oxygen vacancies and acidic centers,and TiO₂ is used as the carrier to improve the degradation activity and stability of CVOCs by using its large specific surface area,surface acidity and selectivity for HCl.SnO₂ has many stable defects and oxygen vacancies due to its low formation energy between Sn gap and oxygen vacancy.It is often studied together with Ce oxide to improve the acidity of the catalyst and the content of oxygen species on the surface of the catalyst.Although ZrO₂ can not directly improve the activity of the catalyst,the mixed oxides of ZrO₂ and TiO₂ can increase the acid sites sharply,and the Ce-Zr solid solution formed by the strong diffusion of Zr in CeO₂ lattice can improve the performance of the catalyst.On the basis of its high catalytic activity and excellent chlorine resistance,Ru is widely considered as an efficient catalyst for the oxidation of CVOCs.More importantly,ruthenium on transition metal oxides can greatly improve the activity and stability of the catalyst,so the selection of ruthenium support is very important.In practical application,H₂O carried in the airflow and H₂O produced by catalytic combustion reduce the activity of the catalyst.So,improving the water resistance of CVOCs catalyst is of great significance to the practical application of the catalyst.Superhydrophobic materials are widely used in various fields because of their water repellency and self-cleaning ability.The larger contact angle enables the droplets to roll down from the surface of superhydrophobic materials in a very small angle.Based on this,ordered mesoporous TiO₂-ZrO₂ and mesoporous CeO₂-TiO₂ supported metal oxide catalysts such as CeSn and Ru are prepared by Evaporation-induced self-assembly.These include:the study of ordered mesoporous TiO₂-ZrO₂ supported CeSn oxide catalyst for the elimination of o-dichlorobenzene,construction of superhydrophobic Ru/TiCeO_x catalyst and application in the catalytic combustion of o-dichlorobenzene to enhance water resistance and catalytic performance.TEM,BET,CA,H₂-TPR,XRD,NH₃-TPD,O₂-TPD,in-situ FTIR,XPS and other characterization techniques were used to study the catalytic materials and the factors affecting the catalytic activity,there result as follow:Ordered mesoporous TiO₂-ZrO₂ materials were prepared by evaporation-induced self-assembly（EISA）.The CeSn/Ti_zZr_10-zO_x catalysts were prepared by impregnation method,and its catalytic performance was evaluated for the removal of o-dichlorobenzene（o-DCB）.The structure and properties of CeSn/Ti_zZr_10-zO_x were characterized by N₂ adsorption-desorption,XRD,Raman,SEM,TEM,XPS and temperature programmed techniques.The results showed that Ce and Sn oxides were highly dispersed on TiO₂-ZrO₂ surface.Ti-Zr mixed oxides not only contributed to the formation of ordered mesopores,but also to the formation of strong acid sites.The CeSn/Ti₆Zr₄O_x catalyst exhibited the excellent catalytic activity and outstanding stability and repeatability for the o-DCB elimination reaction because of its superior chlorine resistance.Furthermore,the reaction mechanism of o-DCB catalytic oxidation reduction was proposed based on surface lattice oxygen.A simple method to enhance the H₂O resistance of Ru/TiCeO_x catalyst for o-DCB catalytic combustion by constructing super hydrophobic coating of phenyltriethoxysilane（PhTES）was proposed.The effect of PhTES content on the pore structure,specific surface area,H₂O resistance,contact angle（CA）value and catalytic activity of the catalyst were studied.When water was added,the pristine Ru/TiCeO_x catalytic activity decreased about 26%,while the Ru/TiCeO_x-16Ph activity hardly decreased.According to the analysis results of XRD,FT-IR,SEM and CA,PhTES was closely coated on the surface of Ru/TiCeO_x to produce a more hydrophobic surface.Ru/TiCeO_x-16Ph catalyst had strong hydrophobicity,and the contact angle was 159.8^o,which not only significantly enhanced the water resistance and self-cleaning activity,but also shown a good elimination temperature(T₉₀=341 ℃)for the o-DCB.The enhanced water resistance of Ru/TiCeO_x-XPh catalysts was results from the reduction of the active centers consumed（water occupying oxygen vacancy sites）.The reaction mechanism of Ru/TiCeO_x-16Ph catalyst based on surface oxygen species and Deacon reaction was proposed.This method provided new idea for the design of a new water-resistant composite catalyst,and promoted the practical application of the composite catalyst in the catalytic oxidation of o-DCB.