SYNTHESIS OF MICROPOROUS TITANOSILICATE ETS-10 FROM TICL3 AND TIO2 - A COMPREHENSIVE STUDY

A comprehensive study of the hydrothermal synthesis conditions which a fford pure and highly crystalline samples of microporous titanosilicat e ETS-10 from TiCl3 and crystalline TiO2 (anatase) is reported. The fo llowing parameters have been studied: fluoride ions, temperature, pH o f the parent gel, sodium and potassium cations, H2O/Si and Si/Ti molar ratios, seeds and time. The best ETS-10 samples are obtained after on ly similar to 15 h (TiCl3) and 24 h (anatase) hours of synthesis at 23 0 degrees C and pH approximate to 10.5 with a Si/Ti molar ratio of 5-6 . By carefully selecting the titanium sources and synthesis parameters , it is possible to obtain crystallites with sizes ranging from simila r to 0.5 mu m (anatase route) to similar to 25 mu m (TiCl3 route). The latter are the largest ETS-10 crystals reported so far. The first ste p in the TiCl3 synthesis is the formation of a silica-titania gel whic h then transforms into ETS-10. The rate-limiting step of the TiO2 rout e is the slow dissolution of anatase followed by condensation with sil icate species which are more readily available in solution. Good-quali ty ETS-10 is easily prepared in the presence of Na+ and K+, without th e addition of fluoride ions. If KC is absent, the synthesis becomes a difficult task and seems to be possible only in the presence of fluori de and under strict control of other synthesis parameters. When the pr ecursor is TiCl3, seeding with good-quality ETS-10 is important, but t his is not so when anatase is used. (C) 1998 Elsevier Science B.V. All rights reserved.