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.