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Aberration-corrected transmission electron microscopy and high-angle annular dark field imaging was used to investigate the surface structures and internal defects of CeO₂ nanoparticles (octahedra, rods, and cubes). Further, their catalytic reactivity in the water–gas shift (WGS) reaction and the exposed surface sites by using FTIR spectroscopy were tested. Rods and octahedra expose stable (111) surfaces whereas cubes have primarily (100) facets. Rods also had internal voids and surface steps. The exposed planes are consistent with observed reactivity patterns, and the normalized WGS reactivity of octahedra and rods were similar, but the cubes were more reactive. In situ FTIR spectroscopy showed that rods and octahedra exhibit similar spectra for OH groups and that carbonates and formates formed upon exposure to CO whereas for cubes clear differences were observed. These results provide definitive information on the nature of the exposed surfaces in these CeO₂ nanostructures and their influence on the WGS reactivity.

Show your face, and we know what you do: CeO₂ nanoshapes have been investigated to determine the exposed surfaces and internal defects. CeO₂ rods and octahedra expose mainly (111) planes, whereas cubes are composed primarily of (100) facets. The nature of the exposed surfaces affects the activity in the water–gas shift reaction as well as the interaction of surface sites with CO.