Structural and Redox Properties of Ceria in Alumina-Supported Ceria Catalyst Supports

Abstract

Several alumina-supported ceria samples with varying ceria contents (1, 2, 10, and 39 wt %) have been studied by different techniques (XRD, Raman, TEM-EDS, UV−vis DRS, XANES, and EPR), aiming to establish a complete model on the structural and redox characteristics of ceria entities in these samples. Two general types of ceria entities are observed: aggregated crystalline ceria species (3D-Ce) and dispersed ceria species in the form of two-dimensional patches (2D-Ce). The relative amounts of each of these species do not show a linear relationship with the cerium loading: as the cerium content is increased, a trend toward formation of 3D-Ce, to the detriment of 2D-Ce, is observed. The EPR data evidence differences in chemical (redox) behavior between 2D-Ce, 3D-Ce, and unsupported ceria. Thus, the main differing characteristic of some 3D-Ce particles with respect to unsupported ceria, which holds true for all 3D-Ce formed with weight percent ≤ 10, is the absence of associated vacancies upon outgassing at ...