Influence of solid-state transformation time on the nucleation and growth of silicalite 1 prepared from layered silicate

摘要

The nucleation and crystal growth of silicalite 1 precursors synthesized by solid-state transformation were studied using X-ray diffraction, thermal analysis, IR spectroscopy, Si-29 and C-13 NMR and electron microscopy. Silicalite 1 was obtained after 16 h at 130 degrees C in a closed glass ampoule. Comparison with hydrothermal synthesis showed that the characterization of the precursors presents some similarities, however, nucleation and crystal growth were much shorter for solid-state transformation. Si-29 NMR showed that nucleation started during the first stage (cation exchange) for solid-state transformation, but only during the second stage for solid-state transformation. It was also observed that the major changes occurred during the beginning of crystal growth for solid-state transformation but during nucleation for hydrothermal synthesis. The results were explained by the fact that the starting materials were completely different: single layered silicate for solid-state transformation and colloidal silica for hydrothermal synthesis. [References: 18]