Influence of alkalinity on particle size distribution and crystalline structure in synthesis of zeolite beta

Abstract

Influence of alkalinity (OH^-/SiO₂) on particle size distribution and crystalline structure in synthesis of zeolite beta at a short crystallization period (60 h) has been studied. The results indicate that the highest crystallinity of synthetic zeolite beta at alkalinity of 0.24, 0.35 occurs when Al₂O₃·H₂O and NaAlO₂ are respectively used as aluminium sources. At an alkalinity higher than 0.39, zeolite beta can not be obtained when Al₂O₃·H₂O is used as aluminium source. The difference of particle sizes between zeolite beta synthesized from gels of different alkalinity is 0.7–0.8 μm. The widest particle size distribution of zeolite beta synthesized occurs when the alkalinity is 0.23–0.24. Along with the increase of the alkalinity, zeolite beta synthesized changes as follows: vibration peak of 1071 cm⁻¹ by IR moves to a higher position, the framework Si/Al ratio determined by ²⁹Si MAS NMR first increases gradually and then decreases, but the change of OhAl/TdAl ratio determined by ²⁷Al MAS NMR is contrary to that of the framework of the Si/Al ratio. In addition, the Si(O⁻) site existing in the TEA-β is confirmed by NMR, and the mechanism of alkalinity influencing crystallization is discussed.