Abstract
The Assembly-Disassembly-Organization-Reassembly (ADOR) process has been used extensively to prepare new zeolite frameworks based on germanosilicate precursors. The disassembly step exploits the lability of the bonds in the presence of water to selectively disconnect the framework, prior to reorganization into new framework topologies.
However, a mechanistic understanding of this crucial step is lacking: specifically, the roles of heteroatom (germanium) content and water loading in zeolite hydrolytic instability. In this work, ab initio free energy simulations, coupled with water vapor adsorption measurements reveal that collectivity effects control the reactivity of the archetypal ADORable zeolite UTL toward water.
A transition between reversible and irreversible water adsorption occurs as water loading is increased, leading to reactive transformations. Clustering of germanium is observed to activate hitherto unreported favorable hydrolysis mechanisms beyond a threshold concentration of three atoms per double four ring unit, demonstrating that the heteroatom distribution and collectivity in the hydrolysis mechanism can drastically influence zeolite framework instability.
These findings suggest that control over heteroatom content, distribution, and hydration level is important to achieve the controlled partial hydrolysis of zeolitic frameworks and is likely to apply not only to other ADORable germanosilicate zeolites but also to Lewis acidic zeolites in general.