| Abstract
| - Faujasite zeolite is synthesized hydrothermally after an aging process under variousconditions. Hydrogel is formed during the aging, and the amount increases with increasingthe duration. Aluminosilicate species included in the hydrogel phase during the aging isinvestigated for the changes in Si/Al ratios and Q units during the aging and the crystallizingprocesses by means of 29Si magic-angle spinning NMR spectroscopy. Aging for more than 1day is necessary to obtain faujasite with high crystallinity. The distribution in Q4 units inthe hydrogel is gradually changed, and the aluminosilicate species having mainly a Q4(4Al)unit is obtained after 7 days of aging, while 2 days of aging results in remanent silicatespecies derived from the starting silica source. The former gives faujasite crystallites withhigher crystallinity, sharper particle size distribution, and a lower Si/Al ratio. On the basisof these findings, the crystallization mechanism is discussed.
- Aging of the precursor solution for FAU zeolite resulted in the formation of aluminosilicate hydrogel. Prolonged aging increased the amount of gel, Q4(4Al) unit in the gel, and the yield and selectivity of FAU, but decreased the crystal size.
|
