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.