Abstract

Aluminosilicate zeolites are traditionally used in high-temperature applications at low water vapour pressures, such as heterogeneous catalysis and gas separation, where the zeolite framework is generally considered to be stable and static. Increasingly, zeolites are being considered for applications under milder aqueous conditions, in emerging fields such as biomass conversion, low temperature oxidation catalysis and medicine. However, it has not yet been established how neutral liquid water at mild conditions affects the stability of the zeolite framework. Here, we show that covalent bonds in the zeolite chabazite (CHA) are labile when in contact with neutral liquid water, which leads to partial but fully reversible hydrolysis without framework degradation. We present ab initio calculations that predict novel, energetically viable reaction mechanisms by which Al-O and Si-O bonds rapidly and reversibly break at 300 K. By means of solid-state NMR, we confirm this prediction, demonstrating that isotopic substitution of ¹⁷O in the zeolitic framework occurs at room temperature in less than one hour of contact with enriched water. The framework is found to heal, with no long-timescale degradation of the framework over at least 200 days. The observation that zeolites are dynamic entities under mild aqueous conditions, with fast breaking of the framework, challenges the conventional view of these materials as static and inert. Considering the industrial importance of zeolites and their growing applications under mild conditions, these findings will be of great importance.