Structural transformation in ceria nanoparticles during redox processes

Using an environmental transmission electron microscope, we followed and characterized the in situ atomic-level redox processes in individual ceria nanoparticles. This is a critical step to understand the redox functionality of catalytically active ceria-based oxide supports in many applications of catalysis. The dynamic redox processes were monitored by simultaneous determination of the structure and chemistry by using high-resolution imaging, electron diffraction, and electron energy loss spectroscopy (EELS). For crystallites with an average size of 20 nm, oxygen vacancies present in the reduced ceria undergo rapid ordering leading to the immediate formation of Ce ₂O ₃. The reduced ceria has C-type structure in which the lattice parameter is doubled compare to that of the parent fluorite phase. The structural transformation is easily reversible during reoxidation and does not appear to involve any intermediate superstructure phases. The ease of the reversibility is important because it provides the structural mechanism for the rapid storage and release of oxygen that takes place in ceria in redox applications.