| Catalytic activity of three-way catalysts (TWC) suffers depression due to the frequent oscillation of Air/Fuel (A/F) ratio in the real practice of gasoline engine. The present thesis investigated the effect of transitional metal doped Ce0.67Zr0.33O2 in modifying the A/F window of TWC, providing a basic understanding for the development of TWCs with broad A/F windows.Noble metal loaded mixed oxides Pd/M-Ce0.67Zr0.33O2-Al2O3 (M=Mn, Fe and Cu) with the doping mole ratio of 5%, 8% and 10% was prepared by a critic acid sol-gel method. Dynamic oxygen storage capacity (DOSC) and TWC test with different A/F ratio were performed to evaluate the A/F window broadening capability of the catalysts. Characterizations including BET and XRD were also conducted for texture analysis.XRD results revealed that the dopants had substituted the locations originally belong to Ce ions in Ce0.67Zr0.33O2 lattice. Mn and Fe doped samples maintained homogeneity phases after hydrothermal ageing at 1050℃for 10h, while inferior thermal stability for Cu doped sample has been indicated by the phase separation among CeO2, ZrO2 and CuO. Mn and Fe doped samples performed advanced DOSC activities in both fresh and aged states, which was contributed by the radius effects, electronic interactions and the redox properties of the dopants. However, DOSC for Cu doped samples decreased in significance for its'poor thermal stability. Water gas shift (WGS) reaction in rich fuel condition had been promoted for Fe and Cu doped samples according to TWC tests'result. CO oxidation and NOx reduction were facilitated by Fe and Mn doping. Mn and Fe dopants in fresh samples broadened the A/F widow of TWC, while the effect of Cu dopants is very limited. After hydrothermal ageing, a severe deterioration of A/F windows had been observed for all Cu doped samples and Mn, Fe doped samples with a doping ratio of 10%. It is safely concluded that 5% Mn and 8% Fe doping optimized the TWC activity and broadened the A/F windows profoundly.
|
PDF Full Text Request