Hydrophobic MFI-Type Zeolites via Alkali-Cation-Induced Defect Healing: Implications for Adsorbent and Catalyst Design.

Abstract

Here, we demonstrate that sub-stoichiometric amounts of alkali cations (Na⁺ and K⁺) critically govern defect formation during the synthesis of Silicalite-1 (MFI), enabling precise control over framework integrity and surface properties after calcination. Combining systematic synthesis studies with density functional theory (DFT) calculations and high-resolution microscopy, we reveal a defect-healing mechanism in which in situ generated NaOH or KOH species promote Si-O-Si bond rearrangement and enhance the mobility of Si(OH)₄ units. This process facilitates the effective healing of T-site vacancies, yielding highly ordered, defect-free MFI frameworks. The resulting Silicalite-1 exhibits markedly enhanced hydrophobicity and superior selectivity in butanol/water separation, underscoring the decisive role of defect control in modulating adsorption and interfacial properties. Importantly, these insights are successfully extended to the synthesis of defect-free TS-1, affording highly hydrophobic Lewis acid catalysts with improved activity and selectivity in the epoxidation of 1-hexene. This environmentally friendly, straightforward, scalable approach offers a versatile pathway to produce defect-free zeolites with precisely tuned physicochemical properties, enabling the development of advanced catalytic and separation materials, especially for applications involving water or polar compounds.