Fig. 4. FTIR spectra of the solid aliquots obtained by (A) RPB and (B) STR premix at different intervals.
To investigate the effect of enhancing micromixing in the zeolite synthetic pathway on the nucleation/crystal growth process, the gel was pretreated by STR for 30 min as a comparison. As shown in Fig. 4, the D5 ring and T-OH structural units’ band pretreated by RPB usually occurred earlier than those by STR. This indicates the enhancement of micromixing during the premix process accelerated the nucleation process of zeolites. XRD results (Fig. 3) further confirm that the crystallization process has been speeded up via RPB premix, accompanied by the growth of the nucleus [29]. The reason is that the water phase (aluminum source), containing a large amount of OH- and TPA+, was mixed thoroughly with the gel phase (silica source) by intensifying micromixing. The water phase provides a high pH environment for the hydrolysis of aluminosilicate and abundant structure-directing agents (TPA+) for assembly of structural units [40,41]. The better micromixing of two phases in the RPB facilitates the faster polycondensation of structural units, resulting in the acceleration of nucleation and crystal growth of zeolites.

3.2 Characterization of the ZSM-5 samples