INVESTIGATION OF NA,TPA-ZSM-5 ZEOLITE SYNTHESIS BY CHEMICAL METHODS

Chemical procedures based on selective dissolution and compleximetric analysis have been developed to provide a simple but informative method for following the course of a high-silica zeolite synthesis reaction. For a dilute Na,TPA-ZSM-5 system, it is shown that amorphous precursor material converts quantitatively into crystalline zeolite product via a solution-mediated reaction-crystallization process. The concentration of silica species in true solution remains relatively constant throughout the majority of the synthesis period during which quasi-equilibrium conditions prevail. The zoned composition of the Na-TPA-ZSM-5 crystal product is shown to be a natural consequence of its evolving reaction environment during the synthesis and corresponds to the changing composition of intermediate crystal samples taken during crystal growth. Acid cleavage of aluminosilicate complexes in the reaction sol provides a means of measuring aluminum lability, which can be related to the incorporation of aluminate into the crystalline product. Radial compositional variation (such as aluminum zoning) in high-silica zeolite crystals can be measured by analyzing the kinetics of their dissolution in excess caustic alkali.