Characterization of titanium silicalite-1 prepared from aqueous TiCl3

Abstract

Titanium silicalite-1 is synthesized using an aqueous solution of TiCl3 as the titanium source. Studies show that the TS-1 (TSR) prepared directly with TiCl3 (Ti3+ was not oxidized to Ti4+ in the gel) is free from extra-framework anatase. TS-1 (TSO) prepared with Ti4+ from the in situ oxidation of Ti3+ can improve the content of matrix titanium in the zeolite. Only a trace of anatase exists when the titanium content in the zeolite is high, up to 2.20 mol%. X-ray diffraction shows that TS-1 samples prepared from TiCl3 are MFI-type zeolite of high purity. Fourier transform infrared spectroscopy indicates that there is a linear relationship between the relative intensity of the 960 cm-1 IR band and the titanium content in the zeolite. Raman spectra reveal that only one titanium phase (highly dispersed form of TiO(x)) is present in the zeolite with titanium below content 2.20 mol%, whereas, above 2.2 mol% titanium, two phases (anatase TiO2 and highly dispersed TiO(x)) are present. However, a considerable amount of anatase exists in TS-1 samples prepared from tetrabutyl titanate even when the titanium content in the zeolite is about 2.1 mol%. Transmission electron microscopy shows that the crystal size of the zeolite changes with the acidity of the precursor. Evaluation of the catalytic properties shows that TSR and TSO samples have a high activity for the epoxidation of allyl chloride and their activity increases with crystallization time. (C) 2000 Elsevier Science B.V. All rights reserved.