Modeling of zeolite L crystallization using continuum time Monte Carlo simulations

摘要

A model to investigate a gel-to-zeolite transformation as a possible growth mechanism through association and rearrangements of extended precursor structures is developed and solved via continuum time lattice Monte Carlo simulations. The model is used to study the morphology of zeolite L nanocrystals grown from an initial amorphous microporous precursor gel. The model considers gel dissolution to release growth precursor extended structures, precursor migration, precursor-precursor association, precursor incorporation into zeolite nanoparticles, and zeolite dissolution. It is shown that the gel-to-zeolite transformation can occur when dissolved precursor migration is slow compared to precursor incorporation and zeolite dissolution. Under these conditions, the initial gel microstructure (intraparticle porosity) has a significant effect on the zeolite morphology and on the crystallization kinetics. This transformation proceeds in two stages: A zeolitic framework forms initially without long-range order, followed by slow rearrangement of building units into nanocrystalline particles with possible defects. Finally different growth modes are identified as a function of microkinetic parameters and gel morphology.