Incorporation of Ti into the framework of aluminium-free zeolite Beta has been achieved in F- medium and has produced hydrophobic selective oxidation catalysts. The Ti−Beta(F) materials have been characterized by X ray diffraction, infrared, Raman, ultraviolet, XANES, EXAFS, 29Si MAS NMR, and 1H→29Si CP MAS NMR spectroscopies, adsorption microcalorimetry, and catalytic testing. At near neutral pH the incorporation of Ti into the framework appears to present an upper limit of ca. 2.3 Ti/uc, beyond which anatase is detected in the calcined materials. However, at higher pH (ca. 11) larger amounts of Ti can be incorporated without anatase formation. After calcination, Ti incorporation in the framework is characterized by an increase in the unit cell volume, the appearance of one Raman band and three infrared bands in the region near 960 cm-1 and the presence of a strong absorption band in the 205−220 nm ultraviolet spectrum. By 29Si MAS NMR, 1H→29Si CP MAS NMR, and infrared spectroscopies it is concluded that upon contact with ambient humidity there is no hydrolysis of Si−O−Ti bonds in Ti−Beta zeolites prepared by the fluoride route, while it is probably a major feature of those synthesized in OH- medium. XANES and EXAFS spectroscopies of calcined dehydrated Ti−Beta zeolites unambiguously demonstrate the tetrahedral coordination of Ti with a Ti−O bond length of ca. 1.80 Å. Upon hydration, the changes in the XANES and EXAFS spectra are consistent with a change in the coordination of Ti to reach a state which depends on the composition and synthesis route and which ranges from a 5-fold coordination for Al-free Ti−Beta synthesized by the F- method to a highly distorted 6-fold coordination in Ti,Al−Beta synthesized in OH- medium. Adsorption microcalorimetry experiments show the strict hydrophobic nature of pure SiO2 zeolite Beta synthesized in F- medium while evidencing a slight increase in the hydrophilicity of the material upon incorporation of Ti to the framework. This is due to the relatively strong adsorption of precisely one H2O molecule per Ti site. On the contrary, the materials synthesized in OH- medium show an enhanced hydrophilicity. Finally, Ti−Beta(F) is an active and selective catalyst for oxidation of organic substrates with H2O2. A comparison of the activities and selectivities of Ti−Beta(F), Ti−Beta(OH) and TS-1 in the epoxidation of 1-hexene using acetonitrile and methanol as solvents demonstrates that the major differences between Ti−Beta and TS-1 catalysts are intrinsic to each zeolitic structure. Because of its high hydrophobicity, Ti−Beta(F) catalyst can advantageously replace Ti−Beta(OH) in the epoxidation of substrates, like unsaturated fatty acids or esters, which contain a polar moiety.

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Pentacoordinated silicon units, SiO4/2F-, were found by solid-state NMR experiments in various as-made high-silica zeolites (Beta, SSZ-23, ITQ-3, ITQ-4, ZSM-12, Silicalite-1) that are prepared in the presence of fluoride ions as mineralizing agents. The SiO4/2F- units are part of the framework, being connected, through sharing of the four O atoms, with four neighboring tetracoordinated SiO4/2 units. These five-coordinate silicon units balance the charge of the cationic organic structure-directing agent. The 29Si chemical shift of these sites is between −140 and −150 ppm, and the 19F chemical shifts are between −56 and −78 ppm. The zeolites SSZ-23, ITQ-4, and Silicalite-1 show a dynamic motion of the fluoride ions at room temperature which is frozen out at a temperature of 130−140 K. In the case of fluoride motion, the 29Si chemical shifts are between −120 and −150 ppm, indicating an exchange between four- and five-coordinate silicon, which means that the fluoride ions exchange between different framework silicon sites. The rigid SiO4/2F- units show a characteristic parameter of the 19F chemical shift anisotropy:  the span value, Ω = δ11 − δ33, is between 80 and 87 ppm.