Fabrication And Performance Of Noble Metal/Oxide Catalysts For Exhaust Purification

It is well-known that gasoline engine exhaust is one of the main sources for air pollution.Three way catalytic technology can reduce emissions of CO,HC?hydrocarbons?and NO_x,simultaneously.Ceria-zirconia complex oxides?CZ?have attracted great attention as the outstanding oxygen storage materials among of three-way catalysts?TWCs?.Their specific surface area and catalytic performance of Ceria-zirconia complex oxides would be significantly reduced at high temperature.When the cerium-zirconium solid solution is calcined at high-temperature reduction??1000 ^oC at H₂?and medium temperature oxidation?in 500 ^oC at O₂?,the?-Ce₂Zr₂O₈ solid solution with highly ordered of cationic substitute structure would be formed,which can greatly improve the oxygen storage capacity of the catalyst and enhance the TWC activity.NO_x,one of the main pollutants released from diesel vehicle and,can be removed using NO_x storage reduction?NSR?technology.Perovskite has been widely applied in NSR filed due to the advantages of easy preparation and high heat stability.The sites-A usually defined with alkalis/alkaline-earth metal sites,which regard as the site of NO_x storage.It has been reported in the literature that acid/base treatment can increase the activity of the catalyst.A series of ceria-zirconia-based solid solutions were prepared with a method of high-temperature reduced treatment followed by middle-temperature oxide.A systematic studies were carried out for the catalytic performance of TWCs,which mainly focus on several aspects:the effects of different temperature on the lattice phase;the surface reconstruction of support after cleaning with alkaline liquid;the decoration of catalysts with noble metal.Based on mentioned above:it can be found that the highly ordered of cationic substitute structure pyrochlore Ce₂Zr₂O₇ phase can be obtained under the 1000 ^oC treatment.The CeAlO₃ new phase appeared once treated under a higher temperature?1200 ^oC?,and it would be worse if further increase the temperature of treatment.Mild re-oxidation treatment of pyr-Ce₂Zr₂O₇ at around 500 ^oC can lead to the formation of?-Ce₂Zr₂O₈.After cleaning with alkaline liquid followed by noble metal deposition,the redox activities,DOSC and TWC of samples were improved.We obtained BaTiO₃ perovskite type composite oxide samples employing citric acid complex method,then cleaned via alkaline liquid and supported with Pt.Catalysts were characterized by methods of XRD,BET and SEM.It was showed that the BaTiO₃ can keep their initial perovskite structure after alkaline liquid treatment,although the specific area decreased slightly.H₂-TPR,NO oxidation,NO_x storage capacity and NSR tests were used to evaluate the activity of the catalysts.It is displayed that once the Pt species supported on the surface,the surface of the catalyst was modified by alkali washing process,then it could enhance the interaction between Pt and Ba by calcination,which exhibited higher activity of redox and NO oxidation as well as NO_x storage ability and facilitated the formation of a reactive nitrite species during the adsorption process.It was confirmed by In situ FT-IR,thus increasing NO_x storage reduction?NSR?activity.BaTi_0.97Pd_0.03O₃ series catalysts were also prepared by citric acid complex method.It were characterized by methods of XRD,BET,SEM and H₂-TPR.It was showed that highly dispersed PdO_x species were formed on the catalyst surface after alkaline washing.NO oxidation,NSC and NSR tests were used to evaluate the activity of the catalysts.It is displayed that NO oxidation ability was slightly improved,and NSR activity was improved.In situ FT-IR confirmed that BTPO-0.5 facilitate the formation of a reactive nitrite species during the NO_x adsorption process.