Influence of Acidity and Phase Intimacy on n‐Hexane Cracking Over USY/ZSM‐5 Binary Catalysts

USY/ZSM‐5 binary catalysts are widely used in fluid catalytic cracking (FCC) catalysts, yet the origin of their frequently reported nonadditive behavior remains unclear. Here, the synergistic effects in USY/ZSM‐5 catalysts are systematically investigated by isolating the roles of composition, BrØnsted acid site density, and phase proximity. Catalysts as intimate, nonintimate mechanical mixtures, and highly intimate composites prepared by quasi in situ interzeolite conversion, were evaluated using n‐hexane cracking at 540°C, a representative FCC probe reaction. Most catalysts indicate independent contributions of zeolites USY and ZSM‐5 acid sites. However, a pronounced synergy is observed when highly acidic ZSM‐5 is combined with USY. Kinetic analysis demonstrates that this effect originates from a mechanistic cooperation rather than from acid‐site interaction or enhancement. The ZSM‐5 component of the binary catalysts promotes olefin formation through monomolecular cracking, while the larger pore architecture of USY favors subsequent bimolecular reactions of these olefins. This results in a strong enhancement of the turnover frequency of USY, reaching nearly an order of magnitude under optimal conditions. These results provide a mechanistic basis for optimizing FCC catalysts using the ZSM‐5 component with an appropriate acidity and pore architecture.