Core–Shell Ni/ZSM-5@SiO2 Bifunctional Catalysts for Enhanced n-Heptane Hydroisomerization via Regulated Metal–Acid Synergy

Improving gasoline octane number while reducing aromatics is crucial for clean fuel production. Herein, a core–shell 2% Ni/ZSM-5-138@SiO2-1 bifunctional catalyst was constructed by coating ZSM-5 with an inert SiO2 shell followed by Ni impregnation. The amorphous SiO2 shell effectively regulated the external surface acidity while preserving the MFI framework and hierarchical pore structure, leading to improved metal–acid synergy and suppressed undesired cracking. Under the optimized reaction conditions, the catalyst achieved an n-heptane conversion of 91.1% and an isomer selectivity of 56.7%. The enhanced catalytic performance is attributed to the synergistic optimization of surface acidity, mass transport, and metal–acid cooperation induced by the core–shell architecture. This work provides a practical strategy for designing efficient bifunctional catalysts for n-heptane hydroisomerization.