| Abstract
| - The influences of Pd sites and specific surface area on oxygen storage capacity (OSC) were investigated overa series of Pd/Ce0.67Zr0.33O2 and Ce0.67Zr0.33O2 samples by CO−He pulse and dynamic CO−O2 measurementsat 300−550 °C. The results show that the rate and quantity of oxygen storage/release capacity are greatlyenhanced by Pd support, showing a more prominent CO2 slope gradient and CO2 reduction peak than that ofCe0.67Zr0.33O2. The existence of Pd−(Ce,Zr)Ox (interface between Pd and ceria−zirconia mixed oxides)interaction is confirmed to be important for oxygen reduction. During the CO−He pulse, acceleration ofoxygen reduction by Pd promotion is limited by the reducibility of the whole system. At low reducibility,Pd−(Ce,Zr)Ox interaction is evident for OSC. Conversely, when the reducibility reaches above 12%, Pd−(Ce,Zr)Ox interaction is less effective, ascribed to the bulk oxygen migration in ceria−zirconia becoming therate-determining step of the reduction process. The experiments with dynamic pulses of CO−O2 reveal thatdynamic oxygen storage capacity (DOSC) is closely affected by the temperature range; DOSC is greatlyaffected by Pd−(Ce,Zr)Ox at low temperature. Considering the effect of Pd deterioration and ceria−zirconiasintering on OSC, after hydrothermal aging at high temperature, no significant difference is related to supportsintering. Additionally, deteriorated Pd sites are more effective in decreasing OSC. Pd site evolution underhydrothermal aging may be dominated by Pd sintering, rather than by Pd encapsulation. By calculating theCO2 production rate, Arrhenius plots are suggested to show that the apparent activation energy increased byPd site deterioration, rather than by sintering of ceria−zirconia.
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