Coarse-Grained Model for the Hydrothermal Synthesis of Zeolites

Abstract

Zeolites are the most used solid catalysts in the chemical industry. The hydrothermal synthesis of these porous aluminosilicate crystals is a multistep process that involves the polymerization of silica from solution to form amorphous aggregates, their crystallization, growth by oriented attachment, and eventually dehydration by heating. The molecular pathways by which zeolites are formed from the precursor solution are not yet fully understood. Molecular simulations can play an important role in elucidating these microscopic processes but are limited by the lack of models able to represent both the polymerization of silica and its crystallization with feasible computational costs. Here, we present a simple, computationally efficient coarse-grained model for the hydrothermal synthesis of zeolites from aqueous solutions. Our TS + W model has three components: silica, a structure-directing agent, and water, each represented by a single particle with short-range interactions. The model quantitatively reproduces the experimental evolution of silica species during the polymerization from solution, yielding amorphous nanoparticles with shape, composition, and silica speciation in agreement with the amorphous precursors of zeolites in experiments. Importantly, the TS + W model spontaneously nucleates and grows zeolites from the amorphous precursor phase and reproduces the temperature required for their dehydration. Our simulations indicate that the preferential formation of zeolites at the amorphous–water interface does not arise from an ability of that surface to heterogeneously nucleate the zeolite. The simplicity and computational efficiency of the TS + W model make it ideal to investigate the interplay between polymerization and crystallization in zeolite synthesis.

Topics & Concepts