The Study On The Solid Solubility Stoichiometric Window Property And Reaction Network For Transition Metal Doping Ceria-based Catalysts

As the key part of the TWC catalysts, ceria-based materials can minimize the fluctuation of air/fuel, thus ensuring that TWCs works effectively under a narrow operating window. On the basis of dynamic oxygen storage/release measurement, dynamic stoichiometric window property, water-gas shift reaction, steam reforming reaction, the effects of intrinsic textural and catalytic properties for the ceria-zirconia doping was investigated, which can provide important information to direct the OSC materials for adapting hostile condition TWC functioned.The mothod for the measurement of stoichiometric window property was founded. The structure, thermal stability, redox and oxygen handling properties and stoichiometric window properity have been analyzed for the different Sr doping samples. The Sr doping resulted in improved phase thermal stability and the low-temperature activity. The introduction Sr into ceria–zirconia lattice strongly modified the mobility of oxygen and enhanced the DOSC performance. Pd-only TWC based on the Ce0.67Zr0.33Sr0.03O2.03 support exhibited superior activity for C3H8 and NO conversion and amplified amplitude of stoichiometric window.The structure, thermal stability and oxygen handling properties have been analyzed for the different Mn, Fe, Co, Ni and Cu doping samples. The transition metal doping improved the dynamic oxygen storage capacity. The light-off temperatures of water-gas shift reaction for the transition metal doping samples are lower than that of undoping sample due to the improved the mobility of oxygen. However, there is a little effect on the steam reforming reaction. The moderate transition metal doping promoted the catalytic activity, however the redundant transition metal in excess of the solubility on the surface interact with Pd, which seriously influenced the catalytic activity. The optimum transition metal doping exhibited amplified amplitude of stoichiometric window; however the stoichiometric window was seriously influenced after hydrothermal aged treatment due to the poorer thermal stability.The CO conversion reaction, C3H8 conversion reaction and the interaction of different reaction were investigated for the Pd/CeO2, Pd/Ce0.67Zr0.33O2 and Pd/Ce0.67Zr0.33O2-Al2O3 samples. The light-off temperature of the CO oxidation reaction shifted to a lower temperature by the addition of water to the feed stream, due to the WGS reactions. The oxidation of C3H8 was enhanced due to the SR reactions. Water-gas shift is favored at low temperature; however steam reforming taken place only at temperature above that necessary to initiate reactions. Steam plays an important role for the catalytic activity.The structure was studied by XRD Rietveld refinement. The maximum solid solubility limit of transition metals (Mn, Fe, Co, Ni and Cu) dissolved in ceria can be described as an empirical equation with parameters such as electronegativity difference, atomic diameter and covalent electrons. The correlative coefficient that the values calculated from the empirical equation is in good agreement with the experimental data. It is indicated that the empirical equation proposed in our work can also be applied to the solid solubility for transition metals Mn, Fe, Co, Ni and Cu doping in ceria.