Characterization of Catalysts Based on Titanium Silicalite, TS-1, by Physicochemical Techniques

Two titanium silicalite-1 samples (A and B) with similar particle sizes have been characterized by powder X-ray diffraction, FT-IR and FT-Raman spectroscopy, UV–visible diffuse reflectance spectroscopy (DRS), transmission electron microscopy with X-ray energy dispersion spectrometry (to analyze grains and ultramicrotomed sections), and xenon-129 NMR. Activity and selectivity for the epoxidation of oct-1-ene by phosphate-free 30% aqueous hydrogen peroxide have been investigated. The critical factors governing the activities of the samples with molar ratios Si:Ti ≈39 (sample A) and 32 (sample B) are the distribution of titanium within the microporous materials and within the extraframework titania (crystalline anatase or amorphous phase as evidenced by UV–visible DRS, FT-Raman spectroscopy, and electron microscopy). Xenon-129 NMR chemical shifts, δexp=f(n) (n=number of adsorbed xenon atoms per gram of anhydrous sample), depend dramatically on extraframework impurities and Ti(IV) dispersion. Pure silicalite and nearly perfect TS-1 (sample A) are not differentiated by xenon-129 NMR, a fact which is tentatively attributed to the “atomic dispersion” of the titanium in sample A, as evidenced by X-ray EDS and by the channel dimensions.