Observations on the role of crown ether templates in the formation of hexagonal and cubic polymorphs of zeolite Y

Intergrowths of hexagonal and cubic polymorphs of zeolite Y have been synthesized using crown-ether templates and the manner of the intergrowth between the polymorphs was studied by high-resolution electron microscopy. The images reveal that both polymorphs grow via a layer mechanism and it is suggested that double-six ring units are the key unit for crystal growth. The growing mechanism accounts for surface structures, defect structures and overall particle morphology. Oscillatory growth occurs in syntheses from multiple crown ether preparations whereby the crystal makeup changes from hexagonal to cubic as surface concentrations of crown ethers fluctuate during crystallization. Finally, the structure directing role of the crown ethers is discussed.