Structural study of Ce_0.9Zr_0.1O₂ nanocatalysts under redox conditions

Full text: The aim of this work is to achieve a better understanding of the structural changes experienced by ZrO₂-CeO₂ mixed oxides under reducing and oxidizing conditions. Two samples, with Ce_0.9Zr_0.1O₂ nominal composition, were studied. One of them with low surface area and the other with high surface area (samples LS and GS respectively). In–situ X-ray powder diffraction (XPD) experiments using synchrotron radiation were performed in different atmospheres (5 mol%H2/He, 5 mol% O₂/He, and 2mol% CH₄ – 4 mol% O₂ He balance) in the r.t to 900°C temperature range. XPD patterns were collected at the D10B-XPD beam-line of the Brazilian Synchrotron Light Laboratory (LNLS, Campinas, Brazil) using a high-intensity and low-resolution configuration, without crystal analyzer. The energy was set at 7997.43 eV and the X-ray wavelength was 1.55031 Å. Sample LS did not show any structural change under the studied conditions. On the contrary sample GS showed cubic fluorite structure until 870°C, with a segregation of a new phase for temperatures up to 900°C. After the reoxidation treatments in 5mol%O₂ this segregated phase disappeared at 750°C, recomposing the original cubic structure. Finally, during in-situ XPD studies in 2 mol%CH₄ – 4 mol%O₂ atmosphere, GS XPD pattern revealed a new peak centered at 26.5°, which appears at 450°C and could be assigned to graphitic carbon formed during methane oxidation. (author)