Upgrading of Isomerate Light Naphtha to Aromatics Over Core-Shell ZSM-5 Zeolite-Mesoporous Silica

This study investigated new core-shell ZSM-5 zeolite-mesoporous silica composites for converting isomerate-rich light naphtha into aromatics using a fixed-bed continuous flow reactor. The core-shell composites were synthesized using a template-assisted sol-gel method, with shell thickness (36–68 nm) controlled by the TEOS (tetraethyl orthosilicate, silica source)/zeolite ratio. Zn was incorporated into the Z23@MS-2 catalyst via wet impregnation. The composites' structure and properties were analyzed using XRD, N₂ adsorption, NH₃-TPD, CO₂-TPD, FTIR, XPS, SEM, and TEM. The catalysts were evaluated for converting isomerate naphtha to aromatics at varying parameters such as Si/Al ratio, TEOS/zeolite ratio, temperature, and WHSV (weight hourly space velocity). The Z23@MS-2 core-shell catalyst (68.2 wt.%) achieved a higher BTEX yield (benzene, toluene, ethyl benzene, and xylenes) than conventional Z23 zeolite (43.3 wt.%) at 550 °C and 0.7 h⁻¹ WHSV, owing to its moderate acidity and accessible pores. Increasing the Si/Al ratio reduced BTEX formation, while the silica shell thickness significantly influenced product distribution. The Zn-modified Z23@MS-2 composite achieved a 74.4 wt% BTEX yield, enhancing dehydrogenation and diffusion from the mesoporous shell. The optimal Lewis to Brønsted acid site ratio was crucial for higher BTEX yields, and the Zn/Z23@MS-2 catalyst was stable over 12 h under optimized conditions.