CHARACTERIZATION OF CATALYSTS BASED ON TITANIUM SILICALITE, TS-1, BY PHYSICOCHEMICAL TECHNIQUES

Two titanium silicalite-1 samples (A and B) with similar particle size s have been characterized by powder X-ray diffraction, FT-IR and FT-Ra man spectroscopy, UV-visible diffuse reflectance spectroscopy (DRS), t ransmission electron microscopy with X-ray energy dispersion spectrome try (to analyze grains and ultramicro-tomed sections), and xenon-129 N MR. Activity and selectivity for the epoxidation of oct-1-ene by phosp hate-free 30% aqueous hydrogen peroxide have been investigated. The cr itical factors governing the activities of the samples with molar rati os Si:Ti approximate to 39 (sample A) and 32 (sample B) are the distri bution of titanium within the microporous materials and within the ext raframework titania (crystalline anatase or amorphous phase as evidenc ed by UV-visible DRS, FT-Raman spectroscopy, and electron microscopy). Xenon-129 NMR chemical shifts, delta(exp) = f(n) (n = number of adsor bed xenon atoms per gram of anhydrous sample), depend dramatically on extraframework impurities and Ti(IV) dispersion. Pure silicalite and n early perfect TS-1 (sample A) are not differentiated by xenon-129 NMR, a fact which is tentatively attributed to the ''atomic dispersion'' o f the titanium in sample A, as evidenced by X-ray EDS and by the chann el dimensions. (C) 1997 Academic Press, Inc.