SYNTHESIS OF SMALL CRYSTALS ZEOLITE NaA BY A TWO-STEP GROWTH APPROACH

Small crystals zeolite NaA were hydrothermally synthesized with a two-step variable-temperature approach, where the hydrogel was first treated at low temperature (283 K) for various times, followed conducted at high temperature (333 K) for 36 h. The products were characterized by XRD, FTIR, SEM and particle size analysis technique. The results indicated that the samples synthesized by a two-step hydrothermal crystallization procedure had smaller particle sizes and narrower particle size distributions than that by an isothermal program. The reasons may be due to that the low temperature at the initial stage was beneficial to the fast nucleation of zeolite NaA with negligible crystal growth, while the crystal growth was dominant at the second stage. Moreover, no peak of other phase or amorphous material was detected in the end samples.