New insights into the structure of a CeO2–ZrO2–Al2O3 composite and its influence on the performance of the supported Pd-only three-way catalyst

Abstract

In this work, a Ce_0.5Zr_0.5O₂–Al₂O₃ (CZA) mixed oxide prepared by a coprecipitation method was deeply investigated and some new insights into the microstructure were obtained. The XRD, Raman, TEM and XPS results revealed that compositional inhomogeneity existed in fresh CZA; some Zr-rich species were in close contact with Al₂O₃, leading to the observed CZ nanocrystallites being richer in Ce, which was detrimental to the oxygen mobility, and consequently an undesirable redox property was obtained. During thermal treatment from 600 °C to 900 °C, atomic rearrangement took place, giving rise to the enhanced homogeneity of CZ solid solutions, accompanied by a weakened interaction between CZ and Al₂O₃, and a homogeneous CZ solid solution with a Ce/Zr ratio approaching the theoretical value of 1 was obtained for CZA treated at 900 °C. The TPR and OSC results indicated that the enhanced homogeneity of the CZ solid solution could facilitate the improvement of the redox property. However, further treatment at 1000 °C brought about the phase segregation of CZ, which led to significantly deteriorated textural and structural properties as well as a worse redox property. As a result, the catalyst Pd/CZA900 (CZA was treated at 900 °C) exhibited the best redox and catalytic performances, as well as excellent thermal stability.