Synthesis of Plate Like Silicalite-1 with Controlled Thickness

Abstract

In this study, plate like Silicalite-1 samples with controlled thickness were synthesized using a SiO2-TPAOH-H 2 O-NH 4 F (TPAOH: tetrapropylammonium hydroxide) system by careful tuning of the synthetic parameters. Samples were fully characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and thermogravimetry-differential thermal analysis (TG-DTA). We confirmed that the concentration of NH 4 F and pH of the initial gel played important roles in controlling sample morphology. The morphologies of the samples changed from ellipse to plate like shapes as the molar ratio of NH 4 F to SiO2 was increased from 0 to 0.18. In addition, the thickness of the plates was controlled by regulating the amount of NH 4 F in the gel. The thickness of the sample decreased as the amount of NH 4 F increased, and reached its minimum when the NH 4 F/SiO2 molar ratio reached 0.4. Further increase of the molar ratio of NH 4 F/SiO2 increased the thickness of the plates because of their improved crystallinity. In these plate like particles, the b axis was perpendicular to the plate, as confirmed by HRTEM, which implies that these materials could show good accessibility for guest molecules because the b axis is the straight channel in MFI structures. All of the plate like Silicalite-1 samples were highly stable and their morphologies were retained even after treatment at 1100℃.