Fibrous silica-modified ZSM-5 zeolites for selective aromatization of light straight-run naphtha

The conversion of light straight-run naphtha (LSRN) into value-added aromatics is an important route for upgrading low-value refinery streams. Conventional ZSM-5 catalysts are effective for aromatization, but their micropore-dominated structure and high acid density can impose diffusion limitations and promote secondary cracking or coke-related deactivation. In this work, fibrous silica-modified ZSM-5 (FSZSM-5) was synthesized by forming TEOS-derived fibrous mesoporous silica around preformed ZSM-5, yielding a micro- and mesoporous ZSM-5 silica composite while retaining the characteristic MFI framework. The fibrous modification increased the external surface area to 318 m²/g and mesopore volume to 0.33 cm³/g, while reducing the total acidity and medium-strong acid contribution compared with parent ZSM-5. Ga and Zn incorporation further tuned the acid-site environment of FSZSM-5, resulting in different pathways for aromatics and light-olefin formation. Ga/FSZSM-5 combined sufficient medium–strong acidity with enhanced Lewis-acid/dehydrogenation character, achieving the highest total aromatic yield of 55.6 wt% with improved xylene formation. In contrast, Zn/FSZSM-5 exhibited enhanced Lewis-acid character but the lowest medium-strong acid fraction and the broadest mesoporous structure, favoring C₂–C₄ olefin-rich products rather than complete aromatization to BTX. Spent-catalyst CHNS analysis showed relatively low carbon deposition within ∼2-4 wt% after the 4 h reaction. These results demonstrate that selective LSRN aromatization requires a balanced combination of mesoporous silica-derived accessibility, sufficient medium-strong acidity, and suitable metal-assisted dehydrogenation character. The fibrous ZSM-5 platform provides a tunable framework for designing metal-zeolite catalysts for light hydrocarbon upgrading.