Study Of Dynamic Oxygen Storage Capacity And Three-way Catalytic Activities Over Pd-CZ-Al₂O₃ Model Automobile Catalyst

As the key part of the Stateâ…¢/â…£three-way-catalyst (TWCs), ceria-zirconia mixed oxides minimize the effect of air to fuel (A/F) fluctuation to catalytic activities and extend the A/F window. On the basis of ceria-zirconia and dynamic oxygen storage/release measurement, the relationship between ceria-zirconia, precious metal and alumina as well as its effects on dynamic oxygen storage capacity (DOSC) and catalytic activities were also studied, aiming at developing advanced Stateâ…¢/â…£TWCs.Combining the XRD, BET, HRTEM, EPR and dynamic oxygen storage/release measurement, effects of intrinsic textural and structural properties, such as surface area, Ce/Zr ratio and alkine earth metal doping etc, on DOSC and dynamic oxygen storage rate (DOSR) were studied. Moreover, in-situ EPR reactor and a set of methods were successfully developed for measuring oxygen vacancy in material. It was shown that DOSC and DOSR are proportional to the surface area and Ce/Zr ratio. Alkine earth metal doping improves the DOSC of ceria-zirconia mixed oxides. Total oxygen storage capacity (TOSC) is proportional to the number of oxygen vacancies in material. The results of in-situ EPR show that oxygen vacancies are essential to Ce/Zr ratio and proportional to oxygen migration.By supporting the Pd on ceria-zirconia, interaction between Pd and ceria-zirconia and its effects on DOSC and TOSC were investigated. When reducibility is lower than 10%～12% and temperature is lower than 450～500℃, Pd supporting promotes the DOSC and DOSR obviously. After hydrothermal aging, both of ceria-zirconia sintering and Pd sintering deteriorate the Pd-(Ce, Zr) Ox interface, as a result of deterioration of DOSC and TOSC. However, compared with sintering of ceria-zirconia, sintering of precious metal has more influence on the OSC deterioration.By mixing the ceria-zirconia and alumina in different mixing scale, DOSC and thermal stability of ceria-zirconia-alumina mixed oxides were investigated. Combining the XRD, BET, XPS, EPR and TEM measurements, mixing scale between ceria-zirconia and alumina is the key factor of improvement of DOSC and thermal stability. Mixing with alumina at small scale improve the distribution and morphology of ceria-zirconia as well as DOSC performance. Whilst mixing with ceria-zirconia at small scale and Ce3+ distribution modifies the surface of alumina and improve the thermal stability.After introducing the Pd into ceria-zirconia-alumina binary oxides, the process of precious metal distribution on binary supports was optimized. The effects among ceria-zirconia, Pd and alumina on DOSC and catalytic activities were investigated. The results show combination of Pd and support, morphology and valence affects the DOSC and catalytic activities. Pd dispersion has less influence on DOSC and catalytic activities. Meanwhile, thermal stability of supports and Pd distribution between ceria-zirconia and alumina play the important role to improve the DOSC and catalytic activities.By charomatagraph distributing the precious metal on single oxide, effects Pd-(Ce, Zr) Ox and Pd (Al₂O₃) on DOSC and catalytic activities were investigated. DOSC and DOSR are more promoted by Pd-(Ce, Zr) Ox than Pd (Al₂O₃). Pd-(Ce, Zr) Ox interface promotes the DOSC and CO catalytic conversion, CO conversion correlate to the DOSC performance; meanwhile, Pd (Al₂O₃) interface promotes the NO and HC catalytic conversion, NO and HC conversion show less relationship with DOSC performance.