Effects of thermal treatment conditions on redox properties of ceria-zirconia materials

Abstract

The nanostructures and redox properties of CeO2–ZrO2 materials can be tuned via optimized thermal treatments. In this study, the CeO2–ZrO2–Y2O3–La2O3 (CZ) materials were prepared by co-precipitation method and submitted to different thermal treatment conditions (atmosphere: nitrogen (N) and air (A); temperature (x): 700, 800 and 900 °C). Due to the protective effects of the “in-situ-formed” carbon powder, treating the surfactants assisted-CZ precursors under N2 atmosphere can keep the pore structures and then the CZ-N700 and CZ-N800 can achieve larger surface area than CZ-A700 and CZ-A800, respectively. In comparison, with high treatment temperature (900 °C), the effects of thermal atmosphere on surface area can be ignored. However, the redox properties of CZ materials correlate closely with thermal treatment atmosphere and temperature simultaneously. As demonstrated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterizations, the N2 atmosphere facilitates the formation of Ce3+ without disturbing the mixing degree of Ce and Zr. Thereby the CZ-Nx materials exhibit superior reducibility than corresponding CZ-Ax materials. In addition, the XRD and XPS results also demonstrate the formation of a more homogeneous CZ solid solution by Zr atoms rearrangement with temperature ignoring the atmosphere. As a result, the reducibility of CZ materials increases with the treatment temperature increasing and is not affected by the worsening of the textural properties. Specially, due to the synergistic effects of N2 atmosphere and high treatment temperature, the CZ-N900 shows the best reducibility. This improvement also emphasizes the important role of structural properties of CZ in explaining the temperature-dependent reducibility.