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