Crystallization kinetics of nanosized Tiβ zeolites with high oxidation activity by a dry-gel conversion technique

The nucleation and crystallization kinetics of Tiβ zeolite was systematically studied with tetraethylammonium hydroxide (TEAOH) as the template and fumed silica as the source of silica by the dry-gel conversion technique under static conditions. The influence of various synthesis parameters such as temperature program, silica and alumina sources, and gel compositions on the formation of Tiβ has been thoroughly investigated. The results suggest that a low temperature in the initial stage favors the nucleation of Tiβ and that the subsequent high temperature is beneficial to the crystal growth. The optimized gel compositions are found to be Si/Al = 120-360, Si/Na = 90-150, Si/Ti = 30-40, TEAOH/Si = 0.4-0.6, and H2O/Si = 40-50. Gel prepared from Aerosil-200 as silica source and with such an optimal composition provides nanosized Tiβ zeolite (20-50 nm) with a high activity in oxidation reactions with H2O2. The presence of a small amount of Na in the gel is a requisite to the crystallization of Tiβ and shows no negative effect on the insertion of Ti into β framework.