Rationalizing Deactivation Behavior in Pyrochlore‐Type CeO ₂ ‐ZrO ₂ Oxygen Storage Catalysts Using Multimodal Nano X‐Ray Fluorescence Computed Tomography, X‐Ray Diffraction Computed Tomography, and Scanning Three‐Dimensional X‐r

The authors report a combination of multimodal scanning three‐dimensional X‐ray diffraction (S3DXRD), X‐ray diffraction computed tomography (XRD‐CT), and X‐ray fluorescence computed tomography (XRF‐CT) used for the first time to provide multiscale (spanning the size regime 0.15–500 µm) insight into the aging of a CeO 2 ZrO 2 solid solution known to exhibit outstanding reversible oxygen storage capacity (OSC). The authors show that using nanobeams is necessary to map in detail the distribution of elements and crystalline phases. In particular, the latter information is derived from two imaging methodologies to capture the diffraction signal originating from single crystals and powder‐averaged crystallites, respectively. Ultimately, a decrease in relative OSC by 25% in the aged material could be correlated with a transformation of the cation‐ordered pyrochlore Ce 2 Zr 2 O 7 phase to the cation‐disordered CeO 2 ZrO 2 fluorite structure. This is manifested as a loss in homogeneity of Ce and Zr distribution of the cation‐ordered pyrochlore seen by nanoXRF‐CT. The diffraction signal in both the S3DXRD and XRD‐CT provides evidence that the solid‐state transformation between the phases preferentially takes place at the periphery of the catalyst particle, resulting in a pyrochlore‐rich core and fluorite on the surface and accompanied by significant sintering.