Crystallinity of large single crystals of FAU-type zeolites with a wide range of Si/Al ratios

Large colorless single crystals of FAU-type zeolites were synthesized from gels with the composition xSiO₂ : 2.0NaAlO₂ : 7.5NaOH : 454H₂O : 5.0TEA, where x = 2.0-6.0. FAU-type zeolite with Si/Al = 1.26(4) was nearly pure and the maximum size of the single crystals was ca. 150 lm. In case of FAU-type zeolites with Si/ Al = 1.54(5), the maximum size of single crystals was ca. 200 lm and the ratio of FAU/impurity was 0.07. The framework Si/Al ratio of the as-synthesized FAU-type zeolite tended to increase with the Si/Al ratio of gel composition. All of the large single crystals had good crystallinities for single-crystal X-ray diffraction, leading to enough numbers of significant reflections which have strong intensity. The structure of a single crystal of dehydrated zeolite Na-X (Si/Al = 1.41(4)) with composition |Na₈₀|[Si₁₁₂Al₈₀O₃₈₄]-FAU per unit cell was determined by X-ray diffraction methods in the cubic space group Fd3m; a = 24.9434(6) Å at 294 K. The structure was refined by using all intensities to the final error indices (using only the 771 reflections for which F_o<4σ(F_o)), R₁ = 0.048 (based on F) and R2 = 0.188 (based on F2). In the crystallographic studies, the Si/Al ratio of the synthetic FAU-type zeolite is 1.41(4) which is quite consistent with the SEM- EDS analysis.