(633d) Structure and Colloidal Stability of Nanosized Zeolite Precursors In the Hydrothermal Synthesis of Zeolite Beta

The crystallization of zeolite beta in solutions composed of 1 SiO₂ : 80 H₂O : 0.5 TEAOH : 0.1 NaOH : Y NaAlO₂ : Z B(OH)₃ where Y is 0 and 0.02 and Z is 0 and 0.05 is shown to proceed through oriented aggregation of nanosized zeolite precursor particles. Direct observation of these precursor particles using cryogenic electron microscopy shows that their structure is affected by the addition of aluminum to the synthesis solution. This result has been incorporated into a small angle scattering model used to characterize the colloidal stability of the precursor particles. It is found that the stability of the secondary particles is dependent upon the type (or number) of heteroatoms (Al or B) in the synthesis solution. Furthermore, there is a correlation between the crystallinity (by x-ray diffraction) of zeolite beta and the rate of precursor particle aggregation. It is suggested that decreasing the rate of aggregation of precursor particles with a growing zeolite crystal enables better alignment of precursor particles with the crystal domain during attachment. This information can be used to develop new strategies for designing crystalline materials with enhanced long-range order and stability.