Preparation Of Hollow Core-shell SiO₂@CeZrTiO_x And Its Catalytic Oxidation Performance For Soo

In recent years,the rapid development of new energy vehicles has replaced some motor vehicles,but the number of heavy tools and trucks using diesel engines is still very large,and a large number of pollutants（CO,HC,NO_x,PM）are released side by side,causing serious damage to the environment.The harmful substance PM（soot particulate matter）in tail gas is one of the main causes of haze weather,which seriously affects human health.At present,the most commonly used technology to deal with PM is diesel particulate catcher（DPF）,whose capture rate can reach more than 98%.However,the captured particles are easy to cause clogging.In this case,catalyst should be coated on DPF to eliminate the trapped soot particles in the lower temperature range（200-500℃）,so as to complete catalytic regeneration（passive regeneration）of DPF.Soot combustion is a typical gas-solid-solid multiphase catalysis and deep oxidation reaction.By increasing the activity of the catalyst and the contact area between the reactants,soot particles can be rapidly burned at low temperature,and the catalyst is the core of this process.Ce-based catalysts have good oxygen release and storage capacity,and are often used for catalytic soot oxidation,but their performance is poor due to poor thermal stability,large differences in catalytic activity and other shortcomings.Therefore,cations（transition metals,alkali metals and alkaline earth metals）need to be doped into Ce O₂ lattice to improve catalytic activity and stability.The physical and chemical properties of Zr O₂ and Ti O₂ are stable.When Zr⁴⁺and Ti⁴⁺are mixed into Ce O₂ lattice,the number of oxygen vacancies increases,and the cyclic transformation between Ce³⁺and Ce⁴⁺accelerates the transport rate of reactive oxygen species,thus improving the catalytic performance of soot oxidation.The morphology of the catalyst also has a great influence on its catalytic activity.When the catalyst has a hollow core-shell structure,it provides a larger reaction space and contact area for the reaction gas,soot particles and catalyst to promote the rapid combustion of soot.In this paper,Ce_xZr_1-xO₂ catalyst（x=1.0,0.9,0.8,0.67）was prepared by hydrothermal method,calcination method and gel sol method to explore its catalytic oxidation performance of soot,and provide a path for the next step of synthesis combined with experimental characterization results.Then,hollow SiO₂ and SiO₂@Ti O₂ spheres were prepared by template method,and then coated with ce-zr-ti composite oxide by hydrothermal method to obtain SiO₂@Ce Zr Ti O_x（S@Cy ZT,y is Ce（NO₃）₂·6H₂O addition/mmol,y=1,2,3,4,5）catalyst for catalytic soot oxidation research.Ce_xZr_1-xO₂ and SiO₂@Ce Zr Ti O_x catalysts were systematically characterized,their microstructure and morphology were observed,and the interaction between Ce,Zr and Ti and the reaction mechanism of the catalysts were investigated.The main research contents are as follows:（1）Ce_xZr_1-xO₂ catalysts were prepared by hydrothermal method,calcination method and gel sol method.It was found that Ce_0.8Zr_0.2O₂-C catalyst prepared by calcination with the molar ratio of cerium and zirconium 8:1 had the best catalytic performance,and its ignition point was 322℃.The order of the catalytic activity of the catalysts prepared by different methods is as follows:Ce_xZr_1-xO₂-C（calcination method）>Ce_xZr_1-xO₂-H（hydrothermal method）>Ce_xZr_1-xO₂-S（gel sol method）.（2）Ce_xZr_1-xO₂ catalyst was prepared by hydrothermal method using NH₃·H₂O precipitation,Na OH precipitation and no precipitation,respectively.It was found that Ce_0.8Zr_0.2O₂-H1 catalyst prepared by precipitation of NH₃·H₂O had the best catalytic activity,and its ignition point was reduced to 338℃.Hydrothermal method（NH₃·H₂O precipitation）was used for the next step of synthesis combining the preparation method and experimental characterization results.（3）A series of hollow core-shell SiO₂@Ce Zr Ti O_x catalysts were prepared by soft template method and hydrothermal method.The results show that S@C3ZT catalyst has the best performance,and its ignition point is 282℃.Compared with Ce_0.8Zr_0.2O₂-C catalyst,the ignition point decreased by 40℃.The ignition point of Ce_0.72Zr_0.14Ti_0.14O₂ catalyst decreases by 26℃and T₉₀ by 41℃compared with that of the catalyst without special morphology.After three cycles of reaction,the Tm of the hollow core shell SiO₂@Ce Zr Ti O_x increased slightly（ΔT_m≤7℃）,indicating its good stability.（4）The activity of the catalyst was tested in the reaction atmosphere of 10%O₂ or10%O₂+2000ppm NO（equilibrium gas N₂）.After the addition of 2000ppm NO in the reaction atmosphere,the T₉₀ of all catalysts were greatly reduced.The T₉₀ of Ce_0.8Zr_0.2O₂-C,Ce_0.72Zr_0.14Ti_0.14O₂ and S@C3ZT catalysts decreased by 39℃,13℃and29℃,respectively.Experiments show that SiO₂@Ce Zr Ti O_x catalyst with hollow core-shell structure is designed and successfully prepared.By introducing Zr and Ti ions into Ce O₂ crystal,the defect concentration of the catalyst crystal increases,and the adsorbed oxygen content on the surface of the catalyst increases,leading to the rapid reaction of carbon smoke to CO₂.The hollow core-shell structure allows NO and O₂ to stay in the sphere for a longer time,generating more NO₂ with strong oxidation capacity,oxidizing soot into CO₂,accelerating the catalytic oxidation rate of soot,and realizing rapid combustion of soot at low temperature.