Tailoring the Reaction Network of n-Heptane Cracking via Framework Fe: From Acid Site Tuning to Kinetic Modeling

Catalytic cracking of naphtha is a pivotal route for light olefin production, yet the rapid deactivation of ZSM-5 zeolites due to coking remains a critical bottleneck. While Fe modification is known to modulate acidity, its specific impact on the reaction kinetic network and the interplay with zeolite topology remain underexplored. Herein, we synthesized Fe-incorporated microporous (CZ) and hierarchical (NC) ZSM-5 zeolites to decouple the effects of framework integrity and mesoporosity. Counterintuitively, the microporous CZ series significantly outperformed the hierarchical NC series, revealing that preserving framework integrity is more critical for Fe efficacy than introducing mesopores, which compromised crystallinity during synthesis. The optimal Fe0.66-CZ catalyst demonstrated superior stability, reducing coke deposition by 74% (2.11% vs 8.05%) and enhancing butene selectivity compared to the parent ZSM-5. Crucially, kinetic modeling elucidates the origin of this coke resistance: although Fe species slightly lowered the barrier for initial oligomerization, they drastically reduced the activation energy for the secondary cracking of heavy intermediates (C7→C2–5) from 69.77 to 50.00 kJ/mol. This kinetic preference facilitates the rapid recracking of coke precursors back into light olefins before they evolve into graphitic deposits. This work provides a new kinetic perspective on designing long-life catalysts by tuning the precursor consumption rate.