2.2. Preparation of zeolite ZSM-5 seeds
The different-sized seeding technique requires zeolite seeds with
different particle sizes that can be produced by different procedures.
In this study, zeolite ZSM-5 seeds with the size of 60 nm, 300 nm and
1.5 μm were prepared with the molar composition of 4
SiO2: TPAOH: 1000 H2O by adding fumed
silica (Sigma-Aldrich, 7 nm, 350-440 m2g−1) and sodium hydroxide (Sigma-Aldrich, 98%) in
tetrapropylammonium hydroxide (Sigma-Aldrich, 1 M). The mixture was then
aged under stirred at room temperature for 24 h until a clear
homogeneous solution was obtained. The seed sizes were controlled by the
method developed by Xia et al. [12] that performs by adjustment of
the synthesis time program during the synthesis. The solution was then
transferred to a Teflon-lined Stainless steel autoclave and placed in an
oven set at 140˚C. After proper synthesis time (3 h, 5 h, and 14 h for
60 nm, 300 nm, and 1.5 μm seeds, respectively), the obtained zeolite
seeds were then purified by repeating rinsing and centrifuging
processes. The XRD patterns of different size synthesized seeds are
presented in Fig. 3, showing that all the seeds used here were pure
crystalline with the characteristic peaks of ZSM-5 zeolite. The
intensity of characteristic peaks enhanced with the increase of seed
size.