Redox behavior of CeO2-ZrO2 mixed oxides: I. Influence of redox treatments on high surface area catalysts

International audienceRedox and textural/structural properties of high surface area ceria-zirconia mixed oxides with composition ranging from 0 to 85 mol% of ZrO2, have been studied using Raman spectroscopy, X-ray diffraction, textural characterization, magnetic susceptibility measurements, temperature-programmed reduction and oxidation, oxygen storage and buffering capacity measurements. Special attention was given to the effects of aging under redox conditions. Correlation between chemical composition, textural, structural and redox properties of the oxides is reported. While for pure ceria almost no reducibility occurs below 773 K, mixed oxides, independently of their composition, exhibit an oxygen storage and buffering capacity at low temperature, which remains stable even after several oxidation/reduction cycles. This improvement with respect to CeO2 is remarkably high in the oxides with high zirconia content and is not affected by worsening of textural properties induced by redox-aging. Phase transformation and/or structural modification are detected as a consequence of the redox treatments, which could be at the origin of such effect

Redox behavior of CeO₂-ZrO₂ mixed oxides: II. Influence of redox treatments on low surface area catalysts

International audienceRedox and textural/structural properties of low surface area (LS) ceria-zirconia mixed oxides with composition ranging from 0 to 85 mol% of ZrO2, have been studied using Raman spectroscopy, X-ray diffraction, textural characterization, magnetic susceptibility measurements, temperature-programmed reduction and oxidation and buffering measurements. Special attention was given to the effects of aging under redox conditions. Correlation between chemical composition, textural, structural and redox properties of the oxides is reported. Comparison with previously reported high surface area (HS) samples shows that in spite of the initial low surface area of the present samples (≈20 versus ≈100 m2g−1), the reduction occurs at fairly low temperatures when zirconium is incorporated into the CeO2 lattice. Remarkably, the favorable effects of the redox-aging on the reduction behavior are more pronounced in the present LS samples compared to the previously investigated HS ones. Raman and X-ray investigations revealed that important modifications of the structure take place as a consequence of the redox aging, leading to appreciable CeO2 segregation, which could suggest some correlation between these parameters

Influence of high temperature treatments under net oxidizing and reducing conditions on the oxygen storage and buffering properties of a Ce_0.68Zr_0.32O₂ mixed oxide

International audienceTPR, TPO, O2 pulses and magnetic balance experiments have been performed to study the effect of two different aging treatments, in oxidizing atmosphere and in reducing conditions, on the redox behavior of a Ce0.68Zr0.32O2 mixed oxide. It has been observed that, although the samples resulting from both treatments have similar textural properties, their redox behavior is significantly different. In particular, aging in H2 improves the oxygen storage capacity (OSC) at low temperatures by decreasing the temperature at which reduction takes place. Also, the oxygen buffering capacity (OBC) is enhanced after aging under reducing conditions. In addition, the study of the re-oxidation of the samples reveals that the rate of the O2 uptake increases if compared with the fresh sample or that aged in air. High resolution electron microscopy and Raman spectroscopy data have also been used to obtain information on the possible origin of such effects