Abstract
Oxygen storage and release with oxygen diffusion in the bulk of the cerium–zirconium solid solution oxide Ce2Zr2Ox (x = 7–8), which possesses an atomically ordered arrangement of cerium and zirconium atoms, is the key to three-way exhaust catalysis. Oxygen storage proceeds via heterogeneous oxygen diffusion into the vacant sites of Ce2Zr2O7 particles, but the heterogeneous oxygen diffusion track is erased after oxygen storage in the Ce2Zr2Ox bulk. Here we show three-dimensional hard X-ray spectro-ptychography to clearly visualize the three-dimensional cerium valence map in Ce2Zr2Ox particles, and unsupervised learning reveals the concealed oxygen-diffusion-driven three-dimensional nanoscale cerium oxidation behavior and tracking areas inside individual mixed-oxide particles during the oxygen storage process. The described approach may permit the nanoscale chemical imaging of reaction tracking areas in solid materials.
Highlights
Oxygen storage and release with oxygen diffusion in the bulk of the cerium–zirconium solid solution oxide Ce2Zr2Ox (x = 7–8), which possesses an atomically ordered arrangement of cerium and zirconium atoms, is the key to three-way exhaust catalysis
3D X-ray spectro-ptychography (XSP) combined with computed tomography (CT) has been demonstrated in the soft X-ray region27–29. 3D XSP in the hard X-ray region is a promising method for visualizing the chemical states inside bulk materials such as CZ-x particles, the huge amount of structural and chemical data in real 3D space visualized by 3D XSP necessitate the efficient extraction of key functional parameters to utilize the obtained data
Nd cluster structures in NdFeB magnets were investigated using 2D transmission X-ray microscopy coupled with X-ray absorption fine structure (XAFS) and unsupervised learning[32], and different modes of crystal growths in cuprous oxide were observed upon visualization of the inhomogeneous internal electronic structures of Cu2O particles by X-ray free-electron laser imaging with manifold learning analysis[33]
Summary
2D XSP in the hard X-ray region has been reported, which provided 2D maps of the Ce density and valence state, suggesting the existence of several 2D domains with different oxygen storage behavior in Pt-supported CZ-x (Pt/CZx) catalyst particles[26]. Significant ambiguities, especially regarding the 3D oxygen-diffusion-driven Ce oxidation tracking areas in individual CZ-x particles during the heterogeneous oxygen storage process, remain in the 2D images derived from projection of the structure and valence state along the optical axis.
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