Ag/Ce-M-O₂ And MnO_x/Ce-M-O₂ Catalysts On Soot Combustion

Diesel vehicles have the characteristic of high fuel economy and good performance of emission,but the number of emissions of particles and NO_x are more than gasoline vehicles,which cause serious environment pollution.The soot and NO_x being inhaled can cause serious damage to the respiratory tract and lungs and may even cause cancer.The thermal oxidation temperature of soot particles is above 550-600?,however,the temperature of diesel exhaust is in the range of 175-400?.How to prepare high activity catalyst while eliminating carbon particles and nitrogen oxides in diesel vehicles exhaust is an important direction,which are applied in the field of catalysis and environmental protection.At present,noble metal exhaust purification catalyst can satisfy the requirement of emission standards,but due to the expensive price,sintering easily at high temperature,poor thermal stability,therefore,exploiting base metal catalyst has gradually become the research focus on exhaust gas purification catalyst.Rare earth metal oxides,CeO₂,due to oxygen mobility,oxygen storage and cycling easily between reduced and oxidized state?Ce3+ and Ce4+?,which is often used as a catalyst material.It has been probed for many researches,for example,CeO₂ combining with transition metal is helpful to increase the oxygen storage,the properties of releasing,enhance oxygen mobility and improve the redox performance and the catalytic activity.In this paper,Ce-M-O₂?M=Sm,Zr?supports with different morphologies?such as short rod?named rodl?,long rod?named rod2?and cube?were synthesized by a hydrothermal method,Ce-M-O₂?M=Sm,Zr?supported Ag or MnO_x were synthesized by an impregnation method,and the Ce?1-x?-AgxO₂ based materials were synthesized by the complexation combustion method.The performances of soot catalytic oxidation were investigated by soot oxidation in air and in NO_x atmosphere.Some interesting results are listed as follow:1.The structure and propeties of Ce-M-O₂?M=Sm,Zr?and supported Ag catalysis were studied.It was found that CeO₂-rod2 has more defect oxygen species compared with CeO₂-rod1 and CeO₂-cube,Ag/CeO₂-rod2 also showed the highest ID/IF2g value?ID/IF2g=1.12?.The redox properties of Ag/CeO₂-rod1 is much stronger by compareing with the other two morphologies catalysts,however,the formation of CeO₂-cube support is more stable easily.The morphology of supports has a strong influence on the property and catalytic activity of Ag/Ce-M-O₂?M=Sm,Zr?catalysts.Ag based catalysts showed a better performance for soot combustion in air atmosphere than in NO_x atmosphere,the dopping of Sm improved the catalytic activity,the best catalytic activity was observed over Ag/Ce-Sm0.1-O₂-cube catalyst with a Tp temperature at about 327?.Mn/Ce-M-O₂ catalysts show lower activity than Ag based catalyst in the soot combustion.2.Different contents of the Ce?1-X?-AgxO₂ based materials were synthesized by the complexation combustion method and the effects of the Ag content on the structure and properties were studied.When the content of Ag is 0.1,the TP temperature is 315? in air atmosphere.It was suggested that the enhancement of interaction between Ag-Ce contributed to the improvement of catalytic activity.