Thermal behavior of (Ce,Zr)Ox/Al2O3 complex oxides prepared by a microemulsion method

Abstract

A study is reported on the thermal behavior of a (Ce,Zr)O_x/Al₂O₃ specimen prepared by a microemulsion method and subjected to aging treatments. A similarly prepared classical CeO_x/Al₂O₃ support was used as a reference. Attention is paid to the 1273–1373 K region of treatment, where previous experience demonstrates that this type of material suffers deactivation processes. The structural/morphological characterization of the complex support was performed using X-Ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. Surface and redox properties were also examined using electron paramagnetic resonance (EPR) and temperature programmed reduction (TPR). The (Ce,Zr)O_x/Al₂O₃ sample contains a mixed oxide component that essentially maintains its structural stability after aging treatment under air at 1273 K although an abrupt loss of the structural homogeneity, leading to segregation into two distinct phases, is produced upon aging at 1373 K. Ce–Zr promoter phases detected during the study maintain the t″ tetragonal symmetry and display a moderate surface composition evolution (small with respect to bulk samples) irrespective of the aging treatment. This is attributed to (Ce,Zr)O_x–Al₂O₃ interactions, which induce beneficial effects on both components, the Ce–Zr promoter and the alumina carrier. TPR experiments show that the aged (Ce,Zr)O_x/Al₂O₃ materials display a low temperature reduction peak around 650 K, which was previously observed only on activated bulk materials subjected to redox cycling, and may be of importance in the oxygen handling properties of these materials.