Density functional studies of model cerium oxide nanoparticles

Abstract

Density functional plane-wave calculations have been performed to investigate a series of ceria nanoparticles (CeO2-x)(n), n <or= 85. Strong correlation effects of the Ce f-electron introduced upon Ce4+ --> Ce3+ reduction have been accounted for through the use of an effective on-site Coulomb repulsive interaction within the so-called DFT+U approach. Twelve nanoparticles of up to 2 nm in diameter and of both cuboctahedral and octahedral forms are chosen as representative model systems. Energetic and structural effects of oxygen vacancy formation in these nanoparticles are discussed with respect to those in the bulk and on extended surfaces. We show that the average interatomic distances of the nanoparticles are most significantly affected by the creation of oxygen vacancies. The formation energies of non-stoichiometric nanoparticles (CeO2-x)(n) are found to scale linearly with the average coordination number of Ce atoms; where x < 0 species, containing partially reduced O atoms, are less stable. The stability of octahedral ceria particles at small sizes, and the predicted strong propensity of Ce cations to acquire a reduced state at lower coordinated sites, is supported by interatomic potential-based global optimisations probing the low energy isomers of the Ce19O32 nanoparticle.

Ceria Nanoparticles as Enzyme Mimetics

“…Loschen et al [82] pointed out that nanoceria with smaller size had higher specific surface areas, more oxygen vacancies and higher Ce 3＋ /Ce 4＋ ratios on their surface. Therefore, control of the nanoceria size could be a method to regulate the enzyme mimetic activities of nanoceria.…”

The origin of the enhanced oxygen storage capacity of Ce1−x(Pd/Pt)xO2

“…water-gas shift reaction, and SO x reductionas well as being a component in gas sensors, intermediate temperature solid oxide fuel cells, and field-effect transistors. 4 The importance of ceria as a catalyst and a support stems from its oxygen storage capacity (OSC), which allows it to release oxygen under reducing conditions and to store oxygen by filling oxygen vacancies under oxidizing conditions. 5 Increasing the number and mobility of oxygen vacancies enhances the OSC and correspondingly improves catalytic activity.…”

Methanol Reactivity on Silica-Supported Ceria Nanoparticles

“…We may only speculate that a relatively higher intensity of the 1108 cm -1 band on particles, commonly assigned to methoxy in atop geometry and which, on the basis of DFT calculations [21], is less stable compared to adsorption on oxygen vacancy, would be consistent with the methanol adsorption on low-coordinated Ce sites present on the particle edges. In addition, the energy of formation of an oxygen vacancy on the surfaces of nanoparticles has been shown to be significantly lower than that of planar surfaces, which leads to much higher oxygen-vacancy concentrations in the nanoparticles, and this property is strongly dependent upon size for small particles [7][8][9]. Moreover, the most energetically favored oxygen vacancies are created at edge sites [8].…”

“…In the latter case, the particles may expose (100) facets as well. Also, Neyman and coworkers [7][8][9] considered octahedral and cubooctahedral particle shapes to be the most stable. Certainly, the morphology of the silicasupported ceria nanoparticles studied here is ill-defined and, in fact, difficult to determine precisely.…”

“…In the case of ceria, density functional theory (DFT) calculations have shown that the formation of an oxygen vacancy is energetically favored on the surfaces of ceria nanoparticles in comparison to extended ceria surfaces [7][8][9]. Indeed, experimental studies have revealed that nanoparticles of ceria have the capacity to support a high concentration of defects and reduced species, which are present in only minute quantities on planar surfaces [10][11][12][13].…”