Phosphorus-Stabilized Hierarchical ZSM-5 for Enhanced Hydrothermal Stability and Selective 1-Hexene Cracking

The development of hierarchical phosphorus-modified ZSM-5 zeolites represents a significant advancement in industrial catalysis. Achieving precise control over acidity, enhancing framework stability, and optimizing product selectivity are critical objectives in this field. Herein, hierarchical P-doped ZSM-5 zeolites were synthesized via a one-step method, using NH₄H₂PO₄ as the phosphorus source. The physiochemical properties of the resulting materials were characterized by XRD, low-temperature N₂ sorption, SEM, XPS, solid-state NMR, Py-IR, and NH₃-TPD analyses. The analyses confirm that the hierarchical zeolites maintain their porosity and crystallinity with phosphorus uniformly dispersed within the framework. After steaming at 800 °C for 4 h, the optimal PHZ-1 catalyst retained 60.3% of its Bro̷nsted acid sites, compared to only 20.2% retention for phosphorus-free HZ, which underwent severe dealumination. In the catalytic cracking of 1-hexene, the optimal PHZ-1 catalyst exhibits superior performance, achieving 97.4% conversion with 58.5% propylene yield and a propylene-to-ethylene (P/E) mass ratio of 6.5, versus 78.4% conversion and 45.2% propylene yield for HZ. This superior performance stems from optimized Bro̷nsted acidity and suppressed hydrogen-transfer reactions enabled by framework P-Al coordination. These quantitative correlations between phosphorus speciation, acid-site preservation, and catalytic performance highlight the strong potential of hierarchical P-doped ZSM-5 zeolites for industrial applications.