| With the worsening of the environment and air quality,the laws and regulations for motor vehicle emission are more stringent.At the same time,diesel,because of whose high thermal efficiency,has been widely applied to large trucks.But how to efficiently and environmentally dispose soot particles,nitrogen oxides and other pollutants which originate from incomplete combustion of diesel has become the primary concern of the whole society.At present,the best way to eliminate soot particles is to reduce the ignition temperature by catalysts,then the soot particles are combusted under the temperature of diesel vehicles（200-500℃）.Therefore,the study of a low-cost,good-performance,environmental friendly de-soot catalyst is the key to solve the exhaust of diesel vehicle.This paper carried out experiment on ceria-based oxides and cerium manganese composite oxide catalytic supported silver,simulated activity of catalyst in the tight and loose contact respectively to test its catalytic activity in the air and NO/O2 atmosphere;characterized the structure of ceria-based compound oxides and their structure-activity relationship through the specific surface area（BET）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,H2 temperature programmed reduction（H2-TPR）.Based on In-situ Infrared characterization,cerium-manganese compound oxide and silver-loaded cerium-manganese compound oxide were placed in different NO atmosphere to investigate the change of nitrogen oxides adsorbed on the surface with the increase of temperature,and then the mechanism of catalytic oxidation of soot was deduced.The composite oxides of Ce-Zr,Ce-Pr and Ce-Mn with different proportions were prepared by sol-gel method.The performance differences of cerium based catalysts for different metal combinations were compared,and the formulation and preparation process of Ce-Mn composite oxide catalysts were optimized.The results of performance evaluation and structure-activity correlation show that the introduction of second metal oxide is beneficial to the formation of cerium-based solid solution,which improve the performance of cerium-based oxide catalyst.Compared with the catalysts of different metallic combinations,it was found that the catalyst activity was the highest when Ce-Mn ratio was 8:2,Tm at loose contact was539℃,and Tm at tight contact was 353℃.Ce-Zr,Ce-Pr and Ce-Mn compound oxides with different proportions were prepared by citric acid sol-gel method,and the properties of catalysis on soot were investigated.It is found that the all three ceria-based catalysts have formed solid solution.In addition to that,the catalytic activity of Ce-Mn composite oxide were higher than the others,and the catalytic activity of C8M2 was the highest,which can ignition soot under 538℃and 353℃in loose contact and tight contact respectively.The metal silver and platinum are loaded on the C8M2 by wet impregnation method,and the properties of catalysis on soot and the correlation of its structure effect are investigated.Ag can greatly enhance the activity of the catalyst,20%Ag catalyst can ignition soot under 312℃.At the same time,with the introduction of Ag,more high valence cerium(Ce4+)conversion to low valence cerium(Ce3+)and more high valence manganese(Mn4+)conversion to low valence manganese(Mn2+/Mn3+),which produce more oxygen vacancies,increase the number of active oxygen and enhance greatly the activity of the catalyst.Silver loaded cerium-manganese compound oxide catalysts for soot combustion mechanism was speculated,which is the following:first,a part of oxidized silver will react directly with soot under low temperature,which generate carbon dioxide;second,the silver catalyst will accelerate the dissociation of gaseous oxygen into surface active oxygen,which accelerate the oxidation of soot;third,NO combined with surface active oxygen under certain temperature change into nitrate that can react with soot directly,which makes soot eventually to be converted to carbon dioxide. |
