Unlocking the Structure-Activity Relationship in Y Zeolites via Synergistic Acidity Tuning and Narrow Mesopores for Heavy Oil Catalytic Cracking

In zeolite catalysis, architecture governs functionality. A long-standing objective in this field has been to achieve simultaneous and precise modulation of both acidic properties and macromolecular conversion capabilities through proactive framework engineering. Addressing this, a small-sized mesoporous DCY zeolite (~5   nm) was synthesized via the SiCl 4 vapor modification developed here. Its properties were evaluated against microporous DY (from conventional SiCl 4 treatment) and large-sized mesoporous USY (~22   nm, from hydrothermal synthesis). DCY significantly enhanced acid site accessibility (Py-IR: 359 μmol/g vs. 283 μmol/g for DY) and mitigated acid site confinement. In particular, DCY zeolite exhibited a higher proportion of Si(1Al) building units relative to Si(0Al) units. This structural feature strengthened the strong Brønsted acid sites and modulated the B/L ratio, thereby optimizing the overall acidity and consequently overcoming the Brønsted acid deficiency in USY caused by its excessive Si(0Al) population. In heavy oil advanced catalytic evaluation (ACE) testing, the DCY-based catalyst demonstrated improved performance: compared to DY, it increased heavy oil conversion (+5.66%) and light oil yield (+5.69%) while reducing coke yield; relative to USY, it reduced dry gas (-0.62%) and coke (-1.31%) yields and optimized product distribution by decreasing C2-C4 alkanes selectivity (-3.3%) and increasing high-value C2-C4 olefins selectivity (+1.4%). This work links "pore–acid synergy" to cracking performance. The synergy improves mass transfer, suppresses over‑hydrogen transfer, and enhances selectivity, providing a basis for designing "oil‑to‑chemicals" catalysts.