Multi Kuarterner Amonyum TuzlarI İle Kristal Gelişimi Sınırlandırılmış Mezoporöz Zeolitlerin Sentezi
Özet
SYNTHESIS OF MESOPOROUS ZEOLITES WITH LIMITED CRYSTAL GROWTH BY USING MULTI-QUARTERNARY AMMONIUM SALTS
Zeolite-like materials such as molecular sieves and mesogözenekous materials have been widely studied in many scientific and industrials areas. With the addition of microgözenekes into the crystalline and mesogözenekous structure of zeolites, the catalytic activity and use of application has been increased. The growth of the crystal framework in three-dimensions causes the formation of deep and complicated channel structures that results with the limitation of diffusion. In this study, it is intended for obtaining nano crystals that have mesogözenekes in between intra-crystalline orderliness in which the crystal growth are limited in specific directions in order to eliminate this limitation. Lately, surfactants that have ammonium groups with the use as structure-directing agents in the synthesis of micro/mesogözenekous materials have drawn attention. In aqueous media, these kind of surfactants have spontaneously formed miscelles that act as a template for the aluminosilicate reactants to form a framework.
Within the scope of the thesis, firstly novel tetra-quarternary surfactants that have four or more carbon chains between ammonium centers were synthesized.
The primary meso-structure that includes the surfactant’s hydrophilic parts and the supramolecular interactions of the aluminosilicate reactants in basic medium, were seen to be in distorted hexagonal packaging. By using the HR-TEM analyses, the aluminosilicate reactants which have formed the boundaries of the hexagonal structure were firstly found to be unstable, then reformed into a layered structure that contains mordenite-like framework, then this structure was observed to transform into a stable zeolite framework in the same medium for the first time. It was found that the microgözenekous zeolite which is shaped in nanorods and 4-5 nm in width per layer was understood that it has similar framework with MFI framework’s powder-XRD analysis. For the 2D (two-dimensional) grown zeolite, XRD diffractogram that explained the crystallinity for all axis could have obtained. The nano-globular structure that is obtained from random ordering of the zeolite nanorods, have their self-pillared nature and includes 4-5 nm width mesogözenekes that provides high external surface area. The transition phase, which is observed for the first time, has a mordenite-like unstable framework, is concluded by the combination of HR-TEM, powder-XRD, SAXS and BET analyses. Polycrystalline product’s morphology which is shown by SEM micrographs are not found in the literature.
