**2. Controllable synthesis of sub-micrometer sized ZSM-5 zeolites**

Batch oxide molar chemical composition of the reaction mixture (hydrogel) for the synthesis was 1.0 Al2O3/100 SiO2/28 Na2O/4000 H2O. A series of silicalite-1 nanocrystals having different mean diameters (90, 180, 220, 260 and 690 nm; Fig. 2) were prepared by synthesis from clear solution and used as seeds for the further growth of ZSM-5 nanocrystals.

Fig. 3 shows that the well crystalline ZSM-5 crystals are obtained after 2 h of hydrothermal treatment at 483K with addition of 4 wt.% of seeds (with respect to the total amount of silica in the reaction mixture). The crystal size of product increases with increasing size of seed crystals as can be seen in the corresponding SEM images (Fig. 4).

On the other hand, using different amount of the same seed crystals (260 nm in this case), the crystal size of the product decreases with increasing amount of added seed crystals (Fig. 5).

Crystallization of Sub-Micrometer Sized ZSM-5 Zeolites in SDA-Free Systems 263

seed (260 nmsilicalite-1 crystals). The scale bars are of 2 μm in (a) and 20 nm in (b). (Adopted

Fig. 4. SEM images of ZSM-5 samples synthesized with using 4 wt. % of: 90 nm (a), 180 nm (b), 220 nm (c) and 690 nm (d) silicalite-1 seed crystals. The scale bars in all the images are of

Fig. 5. SEM images of ZSM-5 samples synthesized by using 4 (a), 8 (b), 16 (c) and 32 (d) wt. % of 260 nm silicalite-1 seed crystals. The scale bars in all the images are of 2 μm. (Adopted

2 μm. (Adopted from Ref. [50] with permission of Publisher.)

from Ref. [50] with permission of Publisher.)

from Ref. [50] with permission of Publisher.)

Fig. 2. SEM images of silicalite-1 nanocrystals with diameters of 90 (a), 180 (b), 220 (c), 260 (d), and 690 nm (e). The scale bars in a-d are of 1 μm, and of 2 μm in e. (Adopted from Ref. [50] with permission of Publisher.)

Fig. 3. The SEM (a), TEM (inset of a), High magnification TEM images (b), electron diffraction (ED) pattern (inset of b) and XRD pattern of ZSM-5, synthesized using 4 wt. % of

Fig. 2. SEM images of silicalite-1 nanocrystals with diameters of 90 (a), 180 (b), 220 (c), 260 (d), and 690 nm (e). The scale bars in a-d are of 1 μm, and of 2 μm in e. (Adopted from Ref.

Fig. 3. The SEM (a), TEM (inset of a), High magnification TEM images (b), electron

diffraction (ED) pattern (inset of b) and XRD pattern of ZSM-5, synthesized using 4 wt. % of

[50] with permission of Publisher.)

seed (260 nmsilicalite-1 crystals). The scale bars are of 2 μm in (a) and 20 nm in (b). (Adopted from Ref. [50] with permission of Publisher.)

Fig. 4. SEM images of ZSM-5 samples synthesized with using 4 wt. % of: 90 nm (a), 180 nm (b), 220 nm (c) and 690 nm (d) silicalite-1 seed crystals. The scale bars in all the images are of 2 μm. (Adopted from Ref. [50] with permission of Publisher.)

Fig. 5. SEM images of ZSM-5 samples synthesized by using 4 (a), 8 (b), 16 (c) and 32 (d) wt. % of 260 nm silicalite-1 seed crystals. The scale bars in all the images are of 2 μm. (Adopted from Ref. [50] with permission of Publisher.)

Crystallization of Sub-Micrometer Sized ZSM-5 Zeolites in SDA-Free Systems 265

Fig. 7. SEM images of the products hydrothermally synthesized (at 438 K for 2 h) from the reaction mixtures (hydrogels) having: *A* = 0.001 (A), *A*= 0.002 (B), *A* = 0.003 (C), *A* = 0.004 (D), *A* = 0.005 (E), *A* = 0.006 (F), *A* = 0.007 (G), *A* = 0.008 (H), *A* = 0.009 (I), *A* = 0.010 (J),

XRD analysis of the products revealed that fully crystalline zeolite ZSM-5 are obtained within the alkalinity range of 0.006 ≤ A ≤ 0.010, which is in accordance with the observation

In order to find more details of particulate properties, the Laser Light Scattering analysis of the obtained samples has been carried out. The particle size distribution (PSD) curves of the samples, measured by Mastersizer 2000 (Malvern) particle size analyzer, are shown in Fig. 8. The crystalline end products obtained under optimal alkalinity range (0.006 ≤ *A* ≤ 0.01) appear as a mixture of single crystals (50 – 60 % by number) having the size between 400

*A* = 0.011 (K), and *A* = 0.012 (L). The scale bars in all figures are of 1 μm.

(Adapted from Ref. [54] with permission of Publisher)

in the corresponding SEM images (Figs. 7F – 7L).

All the products are entirely crystalline and have adjustable size in the range from 270 nm to 1100 nm. This indicates that the SSC approach is a powerful tool for controlling the crystal size of the ZSM-5 zeolites. Besides the crystal size, the morphology of the product could also be controlled via changing the morphology of the seed crystals. The surface-stacking morphology of the silicalite-1 seed crystals (synthesized via microwave heating method) could be fairly well 'cloned' to the final ZSM-5 products (Figure 6). Based on the above phenomena, it could be found that the product properties could be adjusted via a 'seeddependent' manner.

Fig. 6. The silicalite-1 seed crystals with surface-stacking morphology (a) and the corresponding ZSM-5 product (b). The scale bars is of 1 μm. (Adopted from Ref. [50] with permission of Publisher.)
