Application Of CePr Mixed Oxides For Catalytic Removal Of Soot

At present,soot particulates from diesel vehicles exhaust have posed a large threat to the environment and human health.CDPF?catalytic diesel particulate filters?is one of the most efficient ways to control the soot emission.Therein,the key point is exploring a highly active soot combustion catalyst.More and more attentions have been paid to CeO₂ catalyst due to the excellent catalytic soot combustion performance.The doping of praseodymium with appropriate amount is expected to increase the oxygen vacancy on the surface of CeO₂.Further loading of K can enhance the redox properties of the catalyst and the adsorption/oxidation capacity of NO_x.Thus,the more active soot combustion catalyst materials can be obtained.Firstly,Ce_0.5Pr_0.5O₂ mixed oxides were prepared by the reversed microemulsion,microemulsion and coprecipitation method.The structures of the catalysts were characterized by methods of XRD,BET and IR.It was revealed that all catalysts displayed the same phase structure.The samples prepared by reversed microemulsion and microemulsion method have higher specific surface area.The apparent and intrinsic activities of the catalysts were evaluated by TPO?temperature-programmed oxidation?and TOF?turnover frequency?test,respectively.Although the catalyst prepared by microemulsion method had high apparent activity,the catalyst obtained by coprecipitation exhibited the highest intrinsic activity among these three samlpes with different synthesis methods.Generally,in the preparation process of catalysts by coprecipitation method,the drying step has an important effect on the textured properties of catalysts.Therefore,ethanol soaking-vacuum and freeze drying process was employed instead of the common drying process to prepare Ce_0.5Pr_0.5O₂ mixed oxides.Catalysts were characterized by methods pf XRD,BET,IR,H₂-TPR and Soot-TPR.It was showed that the specific surface area of the samples obtained by changing the drying process was nearly doubled compared with that by common drying method,which was comparative to samples prepared by the reversed microemulsion and microemulsion methods.TPO and TOF tests were used to evaluate the activity of the catalysts,respectively.It is displayed that the apparent combustion activity of the samples obtained by ethanol soaking-vacuum and freeze drying were higher than that by common drying under the same test conditions.Also,the larger TOF value was also realized.Based on the above results,K was further loaded to improve the soot removal performance of the catalyst.The physiochemical properties of the K-loaded catalysts were investigated by XRD,BET,IR,H₂-TPR and Soot-TPR.The results showed that the redox performance of the samples was improved after loading of K.The activities of catalysts were investigated by TPO and TOF tests.It was found that the soot combusition activity of K-loaded catalysts was greatly increased compared with samples without K both in O₂ and NO_x atmosphere.Especially,the K-loaded samples displayed higher catalytic soot combusition activity under NO_x atmosphere than that under O₂ atmosphere due to the stronger ability for the adsorption and oxidation of NO_x.