Tailoring Surface Wettability of HZSM-5 Zeolite: A Synergistic Strategy for Boosting Cyclohexene Hydration via Enhanced Mass Transfer and Optimized Acidity

Cyclohexanol, an essential precursor for nylon polymers, is commercially produced via the direct hydration of cyclohexene over HZSM-5. However, this aqueous-organic three-phase reaction suffers from thermodynamically equilibrium limitation and pronounced internal diffusion resistance. In this work, liquid-phase silylation treatment was adopted to purposely adjust the surface hydrophilicity–hydrophobicity of HZSM-5, aiming to promote its catalytic behavior for cyclohexene hydration. The influence of silane type, loading, treatment time, and temperature on catalyst physicochemical features and catalytic performance was investigated. After treatment under optimal conditions (3 g trimethylchlorosilane, 298 K, 1 h), the modified catalyst delivered a single-pass conversion of 12.85%, representing a 13.7% improvement over the pristine HZSM-5. Combined characterizations and catalytic evaluation reveal that a trade-off exists between mass transfer enhancement and acidity loss after silane grafting. Moderate surface hydrophobization facilitates oil–water emulsification and interfacial contact, while silane grafting inevitably reduces zeolite surface area, pore volume, and acid site concentration. Achieving a reasonable balance between these competing effects is therefore critical for maximizing cyclohexene hydration performance.