Rational Synthesis Concept for Cerium Oxide Nanoparticles: On the Impact of Particle Size on the Oxygen Storage Capacity

Stoichiometric cerium oxide nanoparticles with different sizes, ranging between 2 and 12 nm, were prepared by a rational design of the synthetic concept, based on a special hydrothermal procedure. This tuning in particle size was achieved by the decoupling of nucleation and growth, as well as the suitable variation of synthesis temperature and time. In contrast to previous studies utilizing a trivalent cerium compound, we used a tetravalent cerium precursor which results in a cerium oxide powder consisting of single particles with low microstrain and low concentration of bulk defects and, hence, an almost ideal stoichiometry (CeO₂.₀) in the particles’ interior. Owing to these features, the obtained nanoparticles were used as an ideal material for the investigation of the relationship between the particle size and the oxygen storage capacity (OSC). The OSC increased with decreasing particle size, which is expected, as this parameter corresponds to the exchange of oxygen at the surface. By contrast, as a key result, we found that the so-called complete OSC (OSCc) increases with the particle size, which is counterintuitive, as this parameter should not be dependent on the particles’ dimension. Furthermore, these particles allowed for a quantitative description of the Raman redshift of the F₂g mode of CeO₂ in terms of solely the particle size, using theoretical calculations based on the phonon confinement model.