(521h) Stability of Zeolite Y in Aqueous Media: Framework Degradation Under Ambient Temperature and Pressure

Zeolite catalysts are solid nanoporous acids comprised of corner-sharing SiO₄ and AlO₄ tetrahedra, and are widely used in petroleum refining and chemical manufacturing processes. Zeolites have also been found effective in aqueous processes, including biomass processing, which has the potential to be a renewable fuel source. While other catalysts deactivate quickly in the presence of biomass, the tunable shape-selectivity of zeolites could be utilized to design them specifically for biomass feeds. One of the key challenges of utilizing zeolites in biorefining is understanding and improving their hydrothermal stability, as hot liquid water is known to degrade the zeolite’s crystalline framework. Considerable study has been done on the stability of zeolites in the presence of steam, and even in the presence of condensed water at temperatures from 100°C to 200°C, but it has generally been presumed that the zeolite framework is stable in ambient temperature liquid water. While widely accepted, this is not necessarily the case; in fact, solid-state NMR characterization of H-Y which has been soaked in deionized water at ambient temperature and pressure shows substantial framework degradation, even after only 1 hour in water. This aqueous instability may shed new light on the mechanisms of framework degradation and nature of zeolite stability in aqueous processes.