Preparation Of Cordierite-based Diesel Particulate Filter (DPF) And Its Catalytic Regeneration

Diesel vehicles are widely used in the field of vehicles and construction machinery because of their low fuel consumption and high efficiency,but the harmful substances(CO,CH,NOx,PM)in the exhaust of diesel vehicles cause serious pollution to the air.PM(often called soot)in exhaust pollutants are one of the main causes of haze weather,and the haze weather seriously affects our healthy life.The treatment of soot particles is mainly the combination of particle filtration technology and low temperature oxidation technology.The key of the former is the diesel particulate filters(DPF),which is driven by pressure through the surface filtering principle to capture soot particles in the exhaust gas.The particulate matter after capture is easy to cause blockage,so it is necessary to coat the DPF with catalyst to realize low temperature combustion of soot particles,so as to complete the catalytic regeneration(passive regeneration)of DPF.The increasingly strict exhaust emission standards require the catalytic diesel particulate filters(CDPF)to have higher performance and service life.The collection efficiency of DPF filter and the activity of catalyst are the key points.Cordierite is the main material of DPF filter in China.It has low thermal expansion coefficient,good thermal stability,low sintering temperature(about 1300?)and low material cost.However,it has high brittleness and high collecting efficiency corresponding to the increase of filtration resistance.Optimizing the pore distribution of DPF by pore-forming agent can improve the collection efficiency of DPF filter to a certain extent and alleviate the problem of increased filtration resistance.In this paper,the type and content of pore-forming agent were screened to improve the collection efficiency of DPF filter,and the best performance of DPF filter was selected.Ce-based catalyst has high oxygen storage/oxygen release capacity and can effectively reduce the soot combustion temperature.However,the catalytic performance of Ce O₂ is not excellent and has the problems of poor thermal stability.To solve the above problems,the doping of other transition metals or loaded active components can be improved.Ti O₂ has good physical and chemical properties,and the addition of Ce O₂ can improve the stability of the catalyst and the content of reactive oxygen species on the surface to a certain extent,which has the potential research value of catalytic oxidation of soot.Alkali and noble metals are often used as active components of the catalyst to enhance the activity of cerium-based catalyst in oxidation reaction.In this paper,the best performance of Ce_1-xTi_xO₂ catalyst was prepared by sol-gel method,and then supported with active metals to further improve the catalytic performance of soot oxidation.Finally,based on the study of DPF and catalyst,the Ce_1-xTi_xO₂ catalyst with the best performance was coated on the DPF filter to prepare the monolithic catalyst,and the activity of the monolithic catalyst was explored.The specific research work is as follows:1.In this paper,cordierite based DPF was prepared by extrusion molding method and solid-state particle sintering method.The collection efficiency of DPF was controlled by the selection of different kinds and contents of pore-forming agents,and the effects of pore-forming agents on the compressive strength,shrinkage,collection efficiency,pressure drop and other properties of DPF were investigated.Among the three pore-forming agents,polystyrene microspheres(PS),starch and toner,the filter added with 10%PS has the best comprehensive performance:the porosities is 53.8%,the shrinkage rate is 4.15%,the capture efficiency is 98.21%,and the contradictions caused by the increase of the capture efficiency and the increase of pressure drop are the least.2.In this paper,the sol-gel method was used to prepare Ce_1-xTi_xO₂ catalysts with different Ti content.The results showed that the introduction of Ti improved the activity of the catalyst,and part of Ti⁴⁺entered the Ce O₂ lattice to form a solid solution,and the Ce-O-Ti bond was formed at the same time.Ce_0.9Ti_0.1O₂ with 10%Ti content had the best catalytic performance,and the ignition temperature of soot particles was 343?.With the increase of Ti content,the structure of the catalyst is distorted and the Ce-O-Ti fracture occurs,thus reducing the activity of the catalyst.3.This paper uses the impregnation method to load different metals to Ce_0.9Ti_0.1O₂,which are mainly divided into noble metals and alkali metals.Rh,Ru and Pt are selected as precious metals with a load of 1wt.%.The results show that precious metals all improve the performance of the catalyst,which is mainly reflected in the reduction of the ignition point of soot particles and the increase of combustion efficiency.Especially,Rh/C9T1 catalyst has the highest activity among the noble metal with T_i at 335?and T₉₀ at 397?.The alkali metals Na,K,and Cs were selected,and their loading capacity was 8 wt.%.The results showed that alkali metals increased the surface reactive oxygen species of the catalyst,improved the catalytic activity,and reduced the ignition temperature,among which Cs showed the best performance,and the ignition temperature was as low as 321?.4.In this paper,the catalyst Ce_0.9Ti_0.1O₂ was coated on DPF support by the impregnation method.It was found that 2.5 wt.%of the catalyst load can achieve uniform coating,and the catalyst load is low and the catalytic efficiency is high.The ignition temperature T_i=323?.In this paper,the pore distribution of DPF filter was optimized through the selection of pore-forming agent,and the collection efficiency of DPF was improved while the problem of filtration resistance was alleviated to some extent.The best performance of Ce_0.9Ti_0.1O₂ catalyst prepared in this paper may be attributed to the incorporation of a small amount of titanium ions into the interior of Ce O₂ lattice to promote the generation of unsaturated bonds and adsorbed oxygen,which can react with soot to generate CO₂ rapidly.The catalyst supported with active metals not only increases the content of reactive oxygen species on the surface of the catalyst,but also promotes NOx to participate in the process of soot oxidation,which further accelerates the catalytic oxidation rate of soot and realizes the low temperature and fast combustion of soot.