Study On Catalytic Oxidation Of Soot Over Sn-Ce Composite Oxide

The emission of diesel exhaust,especially the soot particles,is one of the main causes of haze weather.Recently,the most effective method to control the emission of soot from diesel exhausts is DPF?Diesel Particular Filters?technology,which burned soot with catalyst by its surface within the exhaust gas temperature range to generate CO₂.In this paper,Sn and Ce were doped by co-precipitation method to prepare a series of catalysts with different proportions(Sn_xCe_1-xO₂,X=0.1,0.2,0.3,0.4,0.5).Catalytic oxidation experiments were carried out under“loose”and“tight”contact conditions with the presence of water.The experimental results show that the Sn_0.4Ce_0.6O₂ catalyst has the best catalytic activity with T90=413?under tight contact conditions and has good selectivity for CO₂ about 90.5%.Then characterization of the catalyst by XRD,XPS,BET,H₂-TPR,Raman,O₂-TPD,TEM,SEM.As a result of the characterization,it is found that when x<0.3,the catalyst exists in the form of a solid solution,and when x>0.3,it exists in the form of a mixed oxides.The addition of Sn with smaller particle size decrease the crystal lattice size of the catalyst and increase the specific surface area that makes Ce⁴⁺converted to Ce³⁺.These reasons lead the synergistic effect and the content of active oxygen increased and the catalytic performance is obviously improved.After four cycles of experiments that the activity of the catalyst remained stable.The alkali metal has a lower melting point and can increase the atomic mobility of the catalyst at a lower temperature,thereby enabling the catalyst to sufficiently contact the soot to increase the catalytic activity.The alkali metal K was supported with different ratios by the impregnation method on the Sn_0.4Ce_0.6O₂ catalyst prepared above,and used for the catalytic oxidation experiment of soot.The experimental results show that the best catalytic effect is obtained when the loading is 15%that the T90 is 388°C,which is about 20°C lower than that of the Sn_0.4Ce_0.6O₂ catalyst,and the selectivity for CO₂ is also increased to 94.3%.In the catalyst after the loading,K is uniformly dispersed on the surface of the carrier,which effectively increases the contact between the catalyst and soot;the increase of the surface oxygen species content also increases the catalytic activity of the catalyst.