Abstract
Zeolites have been synthesized from basic aluminosilicate hydrogel under hydrothermal conditions at elevated temperatures. Since there are various factors affecting zeolite syntheses, the syntheses of zeolite are still based on the experience. Therefore, it is strongly required to understand the crystallization mechanism, resulting in an ultimate goal to synthesize zeolites by rational design. The formation and the consumption of nanosized precursor particles during the synthesis of the nanosized zeolite Linde type A (LTA) from a clear solution using tetramethylammonium (TMA+) cation as an organic structure-directing agent (SDA) was studied by in situ small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). The combination of SAXS and WAXS enables us to observe the particle populations present during the complete course of the crystallization process. Two-sized precursor particles were observed: 2.9nm particles and 11nm particles. The two-sized particles play an important role in the nucleation and the crystal growth of LTA. The size and the distribution of the growing crystals were derived by fitting experimental curves with calculated scattering patterns. A significant narrow size distribution of growing crystals was observed. Based on these findings and further investigations, a mechanism for the formation of organic-mediated nanosized LTA is proposed.
