Reactions of titanium silicalite with protic molecules and hydrogen peroxide

The properties of titanium silicalite (TS-1) in reactions with water, hydrogen peroxide, and alcohol molecules have been studied by means of IR and NMR spectroscopy, and acid activity tests. An IR absorption is shown by TS-1 in the region 900–975 cm−1. Its exact position depends on the amount of adsorbed water, on exchange reactions with 17O- and 18O-labeled water, and on the average size of the crystallites. In 17O MAS NMR spectra a peak is shown at σ 360 ppm from H2 17O (σ = 0). IR and NMR spectra are discussed and interpreted in terms of Ti sites as constituted by tetrahedral [TiO4] units. TiOSi bonds react with water at near room temperature, producing TiOH and SiOH species. Reactions with hydrogen peroxide produce acidic derivatives, which catalyze the hydrolysis of cis and trans 2,3-epoxybutane in methanol, ethanol, and aqueous media. A five-membered ring hydrogen bonded structure, in which a titanium hydroperoxo moiety, TiOOH, and a protic molecule, ROH (R = H, CH3, C2H5), are involved, is proposed for these species. Their possible role in selective oxidations of hydrocarbons is discussed.