Enhancing aromatics selectivity and catalyst stability in castor oil cracking via hierarchical ZSM-5 with tailored mesoporosity

Catalytic cracking of biomass oil offers a sustainable route to aromatics, but conventional microporous zeolite catalysts suffer from low aromatization efficiency and rapid coking. Hierarchical ZSM‑5 zeolites were synthesized by hydrothermal crystallization and alkaline desilication to overcome mass transfer limitations. The alkaline treatment parameters, including NaOH concentration, treatment time, and temperature, were optimized via orthogonal experiments, with treatment time identified as the most influential factor. Under the optimal conditions (0.3 mol/L NaOH, 80 ℃, 3 h), the hierarchical ZSM‑5 delivers an aromatic yield of 39.2%, notably higher than the 26.8% obtained over the pristine ZSM‑5 at 450 ℃. The synergy of hierarchical pores and optimized acidity not only enhances diffusion and coke tolerance, but also promotes deoxygenation and aromatization, thereby reducing deactivation and sustaining stability. In‑situ DRIFTS revealed that the adsorbed castor oil macromolecules crack into oxygenated intermediates upon heating, followed by CO/CO 2 release via decarboxylation/decarbonylation; these intermediates finally aromatize over acid sites to BTX, while polycyclic aromatics and coke form concurrently. This work provides a strategy for designing efficient zeolite catalysts for renewable aromatics production.