Intracrystalline construction and Al-distribution in ZSM-5 zeolites and catalysis for transalkylation of C9 aromatics

• Whole ZSM-5 crystals with identical Si/Al ratios and smooth surface were prepared. • The ZSM-5 with different incrystal mesopores and framework Al-species distribution. • Xylene production in C 9 aromatic transalkylation due to Al in intersection channel. • The incrystal diffusion in ZSM-5 contribute to enhanced catalytic efficiency. • Tandem reaction mechanism for xylene production verified by rapid isomer depletion. The efficient conversion of C 9 heavy aromatics into high-value benzene, toluene, and xylenes (BTX) products is essential for optimizing petroleum refining. This process often depends on both diffusion and the unresolved relationship among structure, acidity, and reactivity of zeolite catalysts. This study focuses on the intracrystalline micro-/ meso -pores in ZSM-5 and decouples the interdependent effects of crystalline morphology and Al distribution of Brønsted acid sites (BAS) in ZSM-5 on C 9 aromatic conversion pathways. The hierarchical ZSM-5 catalysts have the identical SiO 2 /Al 2 O 3 ratios (SAR) and the different distribution of framework Al-species. This dominates the acid distribution of the zeolites and catalytic performances of the catalysts in C 9 aromatic reaction. In toluene/trimethylbenzene (TMB) transalkylation, the hierarchical porosity coupled with reduced crystallite size of the ZSM-5 enhances 1,2,4-TMB conversion by 24.4% and xylene selectivity by 17.9% versus conventional microporous ZSM-5. The product distribution is positively correlated to the concentration of Al atoms localized at channel intersections of the ZSM-5. Diffusion-decoupled experiments demonstrated acid site spatial configuration in the ZSM-5 governs the reaction pathway selection, with aluminum enrichment at channel intersections favoring transalkylation over disproportionation. The hierarchical ZSM-5 in submicron with intracrystalline mesopores and enriched intersection-channel aluminum favors transalkylation of C 9 aromatics to BTX. The hierarchical ZSM-5, with submicron crystallites, intracrystalline mesopores, and enriched intersection-channel aluminum, enhances transalkylation of C 9 aromatics to BTX.