Fabrication And Performance Investigation Of Low Noble Metal Loading Catalyst For Exhaust Emission Purification

With the development of transportation and modern industries,environmental issues have attracted extensive attention.As one of the main sources of air pollution,vehicle exhaust emission standards are getting more and more strict,which puts higher requirements on vehicle exhaust emission control technology.Catalytic oxidation has always been one of the main post-treatment technologies used in vehicle exhaust purification,and its technical core is efficient exhaust purification catalyst.The stringent emission standards have brought new requirement catalysts,meanwhile reducing the amount of conventional precious metal to cut down the catalyst cost is another important issue interested by both academia and industry.Therefore,the development of low precious metal loading or non-precious metal catalysts has become the focus in this research field.With the development of nanotechnology,it has been reported that the nanostructure of metal oxide and the metal/metal oxide interface have great impact on the performance of precious metal/metal oxide nanocatalysts.It is of great significance for the development of new high-efficiency catalysts to deeply understand the structure-activity relationship between the structure of metal oxide supports and the catalytic performance of noble metals.Based on this,we prepared three kinds of nano-titanium dioxide single crystal supports with different crystal phases(anatase,rutile and brookite)by hydrothermal method and loaded with low content of Pd to obtain three kinds of 0.2wt%Pd/TiO2 nanocomposites.The effect of TiO2 crystals on the catalytic oxidation performance of small gas molecules was investigated with low noble metal loading.It was found that the three different catalysts exhibited different catalytic properties.The Pd/TiO2 catalyst with anatase TiO2 as the carrier exhibited the best CO catalytic oxidation activity,and the complete conversion of CO was achieved at 150℃.This difference is due to the different forms of Pd species present on the surface of different TiO2 supports.The Pd species on the surface of anatase and brookite TiO2 are mainly metal Pd nanoparticles,and the Pd nanoparticles on the surface of anatase TiO2 are smaller(2.5nm<3.7nm),while the Pd species on the surface of rutile TiO2 are mainly PdO.The CO in-situ Diffused Reflectance Infrared Fourier Transform Spectroscopy(DRIFTS)also showed a difference in the oxidation process of CO on the surface of those three different Pd/TiO2 catalysts.However,the above catalyst did not exhibit good catalytic activity for propane oxidation,in which further analysis are needed.In addition,based on the low contact area problem existed in commercial Catalyzed Diesel Particulate Filter(CDPF),we designed and synthesized low-content precious metal supported Ag/CeO2/SiO2 core-shell composites.The nano-catalyst is loaded onto the surface of the DPF to prepare a novel CDPF,which not only shows effective catalytic combustion of soot particles but also has good mechanical stability.The results presented in this thesis provide some insights for the design and development of novel and efficient low noble metal loading catalysts.