| The soot particles produced by incomplete combustion of diesel engine internal fuel is one of the main sources of haze,and its emission control is one of the hot topics of current research.The common method to solve this problem is to use diesel engine exhaust soot particle capture device.However,it is prone to increase the pressure of the system,and need to consume extra diesel oil to burn the carbon at high temperature and regenerate the system at short intervals,which affects its reliability and economical efficiency.With the coating of catalyst in the diesel exhaust filter,soot particles can be oxidized at relatively low temperature to realize in-situ regeneration of diesel exhaust particle filter and has attracted wide attentions.The development of efficient catalysts is the core issue of industrialization of this technology.Noble metal catalysts have good activity and stability,but they are not so cost-effective for use.Ce-based oxide catalysts have been widely used in catalytic oxidation,but their activity and stability still need to be improved.In this thesis,two kinds of Ce-based catalysts doped with different metal ions were designed and prepared for on-line catalytic oxidation of soot particles from diesel engine exhaust,and its reaction performance was tested in a fixed-bed reactorA series of CexBi1-xOy and CexSn1-xOy catalysts were prepared by co-precipitation method using NH3·H2O as precipitator.Different elements were doped into the lattice of CeO2 and the effect of doping elements on the activity and stability of Ce-based catalysts were evaluated by adjusting the ratio of doping elements to Ce.The activity and stability of the catalysts were evaluated by temperature programmed oxidation.The catalysts were characterized by XRD,BET,XPS,H2-TPR,C-TPR and Raman analysis.The interaction between Ce-Bi and Ce-Sn and their effects on soot particles were studied.The results were listed as follows:1.CexBi1-xOy catalysts showed good catalytic activity for the oxidation of soot particles.The T10 of Ce0.5Bi0.5Oy catalyst was as low as 320 ?,and the T50 was also reduced to 412 ?.CexBi1-Oy catalysts showed better catalytic performances than pure CeO2 or pure Bi2O3 samples,and its stability was discussed by cyclic stability test.It is found that Ce0.5Bi0.5Oy remains good stability after three cyclic stability tests.The results of H2-TPR,XRD and Raman analysis indicated that Bi was successfully doped into the lattice of CeO2 and a solid solution with strong interaction between Ce and Bi was formed,which resulted in an enhanced reducibility of the CexBi1-xOy solid solution.The doping of Bi also formed a large number of oxygen vacancies in the lattice of CeO2.XPS and C-TPR characterization showed that CexBi1-xOy catalyst samples are rich in lattice oxygen species that are of high mobility at high temperature and spills over to the catalytic surface to oxidize the soot particles at the interface.Oxygen molecules could be adsorbed to the surface oxygen vacancies and transfer to the bulk vacancies to stabilize the crystal structure and also the catalytic activity of the material.2.Catalytic activity of CeO2 was increased via the doping of small amount of Sn,but gradually decreased with increased amount of Sn.The stability of CexSn1-xOy catalysts was studied by aging at 800?for 10 h in a muffle furnace and the activity evaluation showed that the doping of Sn ions could significantly enhance the stability of Ce-based catalysts.It is contributed to the doping of Sn in the lattice of CeO2,which stabilizes the structure of CeO2 and inhibit the growth of particle size at high temperatures.With H2-TPR and XPS analysis,it was found that there is a strong interaction between Ce and Sn.The samples of CeO2 doped with Sn ions contained more adsorbed surface oxygen species after aging than that of pure CeO2 samples,which is beneficial for the performance of catalytic oxidation soot particles.The interaction of Ce-Sn enhances the stability and activity of the catalyst and enlarges the application prospect of the catalyst. |
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