Structural and physicochemical features of titanium silicalites

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.