The review presents a comparison and discussion of the substantial amount of information about the state and coordination of titanium ions in titanium silicalites. The results from structural characterization of titanium silicalites with spectral, electrochemical, and quantum-chemical methods with emphasis on location of the Ti ions in framework or extraframework positions, their coordination, and the relationship of some spectral features to concrete structures at the atomic level are summarized. The main methods for the determination of some specific characteristics of titanium silicalite samples are considered—presence of metal ion impurities, extraframework titania, acidity, hydrophobicity, diffusion, and other sterical restrictions. Speculations on how these properties influence the catalytic activities and selectivities of the samples are discussed. Some experimental results for interaction of molecules—solvents, water, and hydrogen peroxide—with titanium silicalites are also presented. The review could be used as an appropriate basis for continuation of the discussion on molecular aspects of catalytic activity of titanium silicalites in partial oxidation with hydrogen peroxide.

We address the formation of the energetically most favourable single oxygen vacancies in ceria nanoparticles (CeO₂)_n focusing on their size dependence. We study a series of structures with increasing number of CeO₂ units (n = 21, 30, 40 and 80) that, according to well tested interatomic-potential calculations, approach the global minima for these particle sizes. The structures thus obtained are refined by means of density functional (DF) methods, modified by the on-site Coulomb correction. Subsequent DF calculations are performed to quantify and analyse the depletion of atomic O from the nanoparticles that results in the formation of a vacancy O_vac. We show that (i) removal of a low- (two-)coordinate O atom from ceria species requires the lowest energy, in line with evidence from other metal oxides; (ii) the depletion of such O atoms from the nanoparticles is strongly facilitated compared to extended (even irregular) surfaces; (iii) increase of the particle size is accompanied by a dramatic decrease of the O_vac formation energy, implying that at certain sizes this energy should reach a minimum; (iv) the size dependence of the O_vac formation energy is driven by the electrostatics, thus enabling the prediction of the most easily removable O atoms by analysing the distribution of the electrostatic potential in the pristine stoichiometric (vacancy-free) ceria systems. Our findings provide a key to rationalize the observed spectacularly enhanced reactivity of ceria nanostructures.