Preparation and characterization of alumina-rich β zeolites

In SiO₂-Al₂O₃-tetraethylammonium fluoride hydrate-H₂O system with dried silica-alumina gel(n(SiO₂):n(Al₂O₃) 3-14) as alumina sources, low water content and sodium-free or low sodium content, alumina-rich β zeolites were synthesized under the approximate neutral condition at 170°C crystallization temperature in a 3 mL stainless autoclave. The alumina-rich β zeolites synthesized were characterized by means of XRD, SEM, ²⁷Al MAS NMR, XRF and BET to analyze the effects of different crystallization conditions, namely alumina sources, crystallization time, n(H₂O):n(Si+Al), n(SiO₂):n(Al₂O₃) and dried silica-alumina gel calcination temperature on the crystallization process. The results showed that the calcined dried silica-alumina gel was an appropriate alumina source, the suitable n(H₂O):n(Si+Al) was about 3. 5 and the sufficient crystallization time was more than 7 d. When n(SiO₂):n(Al₂O₃) was less than 10, crystallization activity of the dried silica-alumina gel precursors increased with rise of the calcination temperature, and the relative high activity could be reached under the lowest n(SiO₂):n(Al₂O₃) of 7 and calcination temperature of 1000°C. When n(SiO₂):n(Al₂O₃) was more than 10, heightening the calcination temperature would result in decrease of the activity, and single phase alumina-rich β zeolites with n(SiO₂):n(Al₂O₃) of less than 15 and high crystallinity could be obtained when n(SiO₂):n(Al₂O₃) of the precursors was 10-14 and the calcination temperature was 600°C. And the obtained β zeolite particles were aggregations with major microcrystals(0.5-2.0 μm) and a little nanometer crystal grains (30-100 nm).