Zeolite beta mechanisms of nucleation and growth

Zeolite beta has been prepared in dilute (H2O/SiO2 = 80) and concentrated (H2O/SiO2 = 20) conditions. The rates of zeolite beta nucleation and growth in dilute colloidal solutions have been characterized using dynamic light scattering and small angle X-ray scattering. By blending TEA+ and Na+ in dilute solutions at low Al concentration (Si/Al = 50) it has been determined that the presence of Na+ decreases the nucleation rate and increases the growth rate (i.e., decreases the colloidal stability of the precursor nanoparticles) because Na+ competes with TEA+ for surface adsorption sites and occlusion into the precursor particles. Using more concentrated synthesis solutions the role of ion pairs (e.g., [[SiO]− TEA+], [[AlO2]− TEA+], and [[AlO2]− Na+]) in the precursor particles and the zeolite beta product was investigated in detail. Thermal gravimetric analyses have helped determine relation between synthesis conditions and the ion pairs formed in the zeolite beta product. On the basis of the energies associated with these ion pairs a state diagram of zeolite beta including surface structure and phase selectivity has been developed. The relative rates of zeolite beta nucleation and growth have also been investigated at several ratios of TEA+ to Na+ in concentrated solutions. The synergy between these cations and anionic surface adsorption sites has led to synthesis of nearly monodisperse zeolite beta crystal particles having sizes from about 100 to 500 nm.

Thermal gravimetric analyses have helped determine relation between synthesis conditions and [[≡SiO]− TEA+], [[AlO2]− TEA+], and [[AlO2]− Na+] ion pairs formed in the zeolite beta product. On the basis of the energies and excluded volumes associated with these ion pairs a state diagram of zeolite beta including surface structure and phase selectivity has been developed.Figure optionsDownload as PowerPoint slideResearch highlights
► Rates of zeolite beta nucleation and growth have been characterized.
► Na+ decreases the colloidal stability of the precursors leading to enhanced growth.
► Synthesis conditions have been related to the presence of ion pairs in zeolite beta.
► A state diagram for particle size, morphology, and crystal phase has been developed.
► Nearly monodisperse crystal particles between 100 and 500 nm have been prepared.