Creation of Al-Enriched Mesoporous ZSM-5 Nanoboxes with High Catalytic Activity: Converting Tetrahedral Extra-Framework Al into Framework Sites via Post Treatment

ZSM-5 zeolite nanoboxes with accessible meso-micro-pore architecture and strong acid sites are important to heterogeneous catalysis suffering from mass transfer limitations and weak acidities. Rational design of parent zeolites with concentrated and non-protective coordination of Al species can facilitate the post-synthetic treatments to produce mesoporous ZSM-5 nanoboxes. In this work, a simple and effective method was developed to prepare and convert parent MFI zeolites with tetrahedral extra-framework aluminium (EFAL) into Al-enriched mesoporous ZSM-5 nanoboxes with low silicon-to-aluminium ratios (SARs) of ~16. The parent MFI zeolite was prepared by a strategy of rapid ageing of the zeolite sol gel synthesis mixture. The accessibility to the well-developed meso-micro-porous intra-crystalline network was probed systematically by comparative pulsed field gradient nuclear magnetic resonance measurements (PFG-NMR) diffusion measurements, which, in synergy with the high concentration of strong acidity of nanoboxes, provided superb catalytic activity and catalyst longevity in hydrocarbon cracking for producing propylene.