| Abstract
| - Pt and Pd particles supported on a texturally stable Ce0.68Zr0.32O2 mixed oxide were investigated by means ofH2 chemisorption and high-resolution transmission electron microscopy (HRTEM). The comparison of themetal dispersion data as determined by HRTEM with those estimated from H2 volumetric adsorption revealsthat, in the case of Pt catalysts reduced at temperatures below 350 °C, the chemisorption isotherms recordedat −80 °C provide reliable dispersion data. For catalysts reduced at, or above, 350 °C, some platinumdeactivation occurred. However, H2 chemisorption capability was recovered by reoxidation at 427 °C andfurther reduction at 150 °C. For catalysts reduced at 700 °C or 900 °C, the recovery of the platinumchemisorptive capability was only partial, even if a more severe reoxidation treatment (700 °C) was applied.To prevent hydride formation, H2 chemisorption on the Pd/Ce0.68Zr0.32O2 was investigated at low H2 pressuresand at room temperature. Under these experimental conditions, which are often employed for characterizingPd catalysts, hydrogen spillover cannot be blocked, thus preventing a reliable estimate of the metal dispersionin our ceria−zirconia -supported palladium catalysts.
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