Catalytic Oxidation Removal Of Soot Particles From Diesel Engines Over Cerium-based 0xide

Diesel engine due to the high fuel efficiency, large power, lower CO and volatile organic compounds（VOC） emissions and other advantages, widely used in heavy duty and long-distance truck. However the removal emitted from diesel engine of soot particles size is less than 0.3 μm is an important concern due to the health and environmental problems. To effectively remove carbon exhaust smoke, can be combination with resistant high temperature DPF and low temperature combustion catalyst to removed, the catalysts activity and stability is very important. Ceria-based oxides, specially ceri-zirconium composite oxides are of considerable interest because they have potential applications in catalysis, electrochemistry, and optics due to the unique physical and chemical properties. Based on ceri-zirconium composite oxide as the research object, through different synthesis method and doping modification on catalytic system to study catalyst carbon smoke combustion performance. The structure and activity of the prepared catalysts were characterized by X-ray powder diffraction（XRD）, specific surface area（BET）, scanning electron microscopy（SEM）, X-ray photoelectron spectroscopy（XPS）, Fourier infrared（FT-IR）, H₂- temperature programmed reduction（TPR） and temperature programmed oxidation（TPO） technology evaluation. The results show as follows:1. A series of Ce_0.8Zr_0.2O₂ catalysts were prepared by citric acid sol-gel method,low temperature co-precipitations,high temperature co-precipitations,hydro-thermal,physical mixed 5 method. The effects of physico-chemical properties of catalysts on the catalytic performance under different catalysts-soot contact condition were investigated. The results indicated that the Zr4+ were incorporated into ceria lattice to form a pure Ce_0.8Zr_0.2O₂ solid solution for the 5 method sample. Under loose contact condition, specific surface area（SBET） of catalysts may be the primary factors that determine the catalytic activity, synthesized by hydro-thermal method of Ce_0.8Zr_0.2O₂ by has the largest SBET showed the highest catalytic soot combustion ability. Under tight contact condition, catalyst reduction performance and oxygen storage capacity may be the key factors that influence on catalytic performance of catalyst, synthesized by citric acid sol-gel method of Ce_0.8Zr_0.2O₂ samples for optimal reduction ability and maximum oxygen storage showed the best catalytic soot combustion activity.2. A series of Ce_0.65-xCo_xK_0.15Zr_0.2O₂ were prepared by sol-gel method using citric acid as complex agent. The results indicated that the catalyst showed reticular and porous structure, Co ion did not excess dissolve into the ceria lattice and Co3O4 highly dispersed on the surface of sample. The number and size of surface Co3O4 particles and cobalt-ceria solid solution of which the former is the main active phase and latter is the stable phase responsible for the high activity and stability. When x=0.23, catalyst showed the highest activity（Ti and Tm were 321 and 355℃ ℃） due to many active tiny Co3O4 particle scattered on sample surface, But the Co3O4 particles easy deactivation after 800 ℃ in air atmosphere aged treatment. It was found that the x as 0.15, catalyst relatively did not exhibit excellent catalytic activity before aged, but after aged for contribute to many solid solution possessed better activation and thermal stability, in which the values of Ti and Tm were 375 and 439℃ ℃.3. This work presents a study of sol-gel-impregnation methods for catalyst supported on SiC. The results show that all the catalysts are active in soot combustion with a significant decrease of oxidn. onset temp. after supported on SiC. It is found that the catalyst K-Co-Ce-Zr/SiC displays the lowest characteristic temps, including the initial and maximum combustion temps（Ti and Tm）. The Tm and average oxidation rate is 428 and 17.01 ℃μg/s, respectively. The catalyst K-Co-Ce-Zr/SiC after cycling 5 times still showed superior activity and high stability. The activity of the catalyst Ce-Zr/SiC is improved by doping Co species, which result in increasing the activity of surface oxygen, whereas K species existed in the catalyst mainly contributed to improving the contact between catalysts and soot which can improve the catalytic activity of the catalyst.