In this work, Ce 0.5 Zr 0.5 O 2 -Al 2 O 3 (CZA) mixed oxide prepared by coprecipitation method was deeply investigated and some new insights into the microstructure were obtained. The XRD, Raman, TEM and XPS results revealed that there existed compositional inhomogeneity in fresh CZA, some Zr-rich species closely contact with Al 2 O 3 , leading to the observed CZ nanocrystallites richer in Ce, which was detrimental to the oxygen mobility and consequently undesirable redox property was obtained. During thermal treatment from 600 ºC to 900 ºC, atom rearrangement took place, giving rise to enhanced homogeneity of CZ solid solutions 2 accompanied by weakened interaction between CZ and Al 2 O 3 , and a homogeneous CZ solid solution with Ce/Zr ratio approached the theoretical value 1 was obtained for CZA treated at 900 ºC. The TPR and OSC results indicated that the enhanced homogeneity of CZ solid solution could facilitate the improvement of the redox property. However, further treatment at 1000 ºC brought about phase segregation of CZ, which led to significantly deteriorated textural and structural properties as well as worse redox property. As a result, the catalyst Pd/CZA900 (CZA was treated at 900 ºC) exhibited best redox and catalytic performance as well as excellent thermal stability.Recently, large amount of research attention has been focused on Pd-based catalysts with low metal loadings on account of its comparatively low expense and outstanding low-temperature oxidation activity of HC and CO. 3,6,11,12 Al 2 O 3 is one of the most commonly used support materials in three-way catalysts, and CeO 2 -ZrO 2 mixed oxide is an indispensable component which acts as an oxygen storage/release material. Owing to the synergistic interaction between CeO 2 -ZrO 2 and Al 2 O 3 , the combination of them has been systematically investigated by many researchers. [13][14][15][16][17][18][19][20] And their results demonstrated that CeO 2 -ZrO 2 -Al 2 O 3 system displayed improved textural property, modified redox property and enhanced thermal resistance compared with single CeO 2 -ZrO 2 or Al 2 O 3 .In the early stages, CeO 2 -ZrO 2 -Al 2 O 3 composites were usually synthesized by wet-impregnation method, 13,14,21-23 sol-gel technique 24,25 or simple mechanical mixing route, 26-28 only recently coprecipitation method has been widely applied to prepare CeO 2 -ZrO 2 -Al 2 O 3 6,17,29-36 in order to homogeneously mix the various components in molecular level, and it appears that CZA obtained by this method usually exhibits better structural, redox performance as well as higher thermal resistance, making it more desirable as a candidate to apply in TWC. Up to now, when the combination mode of CZ and Al 2 O 3 in CZA prepared by coprecipitation method is concerned, there still exist various opinions, among which some contradictory results have been found. Some authors consider that Al 2 O 3 enters into the CZ lattice to form homogeneous solid solutions, 19,29,37 while other researchers 16,17,31,38 have reported that there consists of t...
