Enhanced Esterification of Benzyl Alcohol with Acetic Acid using Sulfated Metal-Incorporated MCM-48: A Stable and Reusable Heterogeneous Catalyst.

Abstract

Sulfated metal-incorporated MCM-48 mesoporous silicates were synthesized hydrothermally using tetraethyl orthosilicate (TEOS) as the silica precursor and cetyltrimethylammonium bromide (CTAB) as the structure-directing agent. The materials were extensively characterized through techniques, such as powder X-ray diffraction (PXRD), N₂ adsorption-desorption, diffuse reflectance UV-vis spectroscopy (UV-vis DRS), Fourier transform infrared spectroscopy (FT-IR), NH₃-temperature-programmed desorption (NH₃-TPD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), and inductively coupled plasma optical emission spectroscopy (ICP-OES). PXRD confirmed the retention of the well-ordered MCM-48 structure in the modified materials, while UV-vis DRS revealed partial incorporation of metal ions in their preferred tetrahedral coordination within the framework. Mesoporosity was verified through N₂ adsorption-desorption isotherms, and NH₃-TPD results showed enhanced acidity in the sulfated catalysts. Catalytic performance was tested in the esterification of benzyl alcohol with acetic acid under liquid-phase conditions. The optimized reaction parameters, using a 9% (w/w) S-Fe-MCM-48 catalyst, a benzyl alcohol to acetic acid molar ratio of 2:1, a temperature of 60 °C, and a solvent-free system over 6 h, yielded benzyl acetate with 98.9% selectivity as the major product. Reusability tests demonstrated the robustness of the S-Fe-MCM-48 catalyst over five successive cycles, indicating its potential suitability for industrial applications.