Spectroscopic characterization of silicalite-1 and titanium silicalite-1

Titanium silicalite samples were prepared by two different procedures. A titanium-free sample (silicalite-1) was also prepared. The samples were characterized by XRD, SEM, skeletal ET-FIR and FT-Raman, UV-vis FT-IR of hydroxy- groups and of adsorbed ammonia. The skeletal spectra have been analyzed on the basis of a general interpretation of the vibrational structure of tetrehedra-based silica polymorphs. This lead to a partial modification of the traditional assignments of the skeletal vibrations of zeolites, Framework Ti is found to be responsible for a band near 960 cm(-1), in both IR and Raman spectra, and for a shoulder near 510 cm(-1) in the IR spectra, as well as for other weak perturbations of the silicalite spectra. The two main features have been assigned to the asymmetric stretching and to the rocking modes of Si-O-Ti bridges. Framework Ti is found to act as a Lewis acid center, being able to coordinate ammonia from gas-phase. Extraframework Ti is observed in the form of anatase in samples prepared with the procedure 1 only with Ti content above 2%, while TiO2 is found in all samples prepared with the procedure 2. Both series of samples are active catalysts of phenol hydroxylation by H2O2. (C) 1995 Academic Press, Inc.