The influence of gel alkalinity in the synthesis and physicochemical properties of the zeolite [Ti,Al]-Beta

Zeolite [Ti, Al]-Beta has been synthesized by two methods (Method I and II) using aluminum (Al(NO3)3 · 9H2O) and varying the initial gel alkalinities (OH−/TIVO2). Both methods employed silica (SiO2), hexafluorotitanic acid (H2TiF6), tetraethylammonium hydroxide (TEAOH) and ammonium fluoride (NH4F) as silicon and titanium sources, template and crystallization additive, respectively. X-ray powder diffraction and chemical analyses were used to examine crystallinity and framework elements composition in the solid samples. DR-IR/DF-UVis spectroscopy and scanning electron microscopy (SEM) were used to study the influence of initial gel alkalinity in the particle size and crystallization mechanism of solid samples. In general, higher solid yields were obtained for relatively shorter crystallization times in samples crystallized from more alkaline gels (Method I). No zeolite Beta crystallized from gels with OH−/TIVO2 lower than 0.42 using Method II. Samples of higher crystallinity were obtained for crystallization times >132 h using Method II. Samples of Method I synthesized from less alkaline gels contained higher Ti and lower Al contents. The intensification of the IR band at 960 cm−1 and the UV absorption at 212 nm observed in calcined samples proved tetrahedral Ti in the Beta framework. SEM micrographies revealed smaller average zeolite particle size in samples crystallized from more alkaline gels using Method I.