Synthesis of Al–Si-beta and Ti–Si-beta by the aging–drying method

Abstract

Al–Si-beta and Ti–Si-beta were synthesized by the aging–drying method in fluoride medium without seeding and using tetraethylammonium hydroxide as organic structure-directing agent (OSDA). In the aging–drying method the gels are allowed to release some volatile species (mainly ethanol and water). Samples with molar batch composition: SiO 2:0.54TEAOH:0.7HF: xH 2O: yM n + F n - (where x ≈ 10, y = 0.02, M = Al or Ti) were aged and dried during about one week. Organic solvents were added to selected aged–dried gels to determine their role as complementary OSDA. All samples were hydrothermally treated at 140 °C during 1–12 days. After crystallization, samples were characterized by PXRD, SEM, TGA-DTG, FTIR, atomic absorption, low temperature nitrogen adsorption, 29Si MAS NMR and 27Al MAS NMR. Pure and well-crystallized zeolite beta samples were obtained in all experiments performed. Polymorph A enrichments of about 69% and 64% were reached for Ti and Al loaded samples, respectively. Al-loaded samples exhibited small average crystal sizes compared with Ti-loaded samples. The incorporation of Al in the beta framework was proven by several techniques and the Al/Si ratios were similar to those of the precursor gels. However, Ti incorporation was quite low.