Regionally spatial framework Al distribution in MFI channels and its impact on the n-butane cracking reaction pathways

• Published in: Fuel (Guildford) 2023-12, Vol.353, p.129230, Article 129230
• Main Authors: Guan, Linjie, Liu, Meiyu, Liu, Honghai, Zhang, Li, Zhang, Yiming, Qin, Yucai, He, Binbin, Mei, Yi, Zu, Yun
• Format: Article
• Language: English
• Subjects: Cracking reaction pathways; Framework Al distribution; Light olefins; n-Butane; ZSM-5 zeolite
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2023.129230

[Display omitted] •ZSM-5 zeolites were synthesized by employing various OSDAs and Na cations.•Regionally spatial framework Al distributions in MFI channels are investigated.•Framework Al distributions intensely control n-butane cracking reaction pathways.•Framework Al sited in straight or intersection channels favors propylene production. The regulation of the engineering regionally spatial framework aluminum (AlF) distribution in MFI channels has been considered as an effective way for the production of light olefins by targeted fluid catalytic cracking (TCO) technology. In this work, ZSM-5 zeolites with controlled AlF distributions are facilely synthesized by tuning the combinations of pentaerythritol (PET), tetrapropylammonium (TPA) and Na cations. The AlF atoms in the prepared HZ5-[PET + Na] and HZ5-[TPA] samples are enriched in the straight channels and intersection channels, respectively, which are favorable to the n-butane monomolecular reaction pathway, promoting the propylene production. Whereas the AlF atoms in the HZ5-[TPA + Na] sample are simultaneously distributed in both the straight and intersection channels, the n-butane molecules preferentially take place monomolecular reaction in the straight channels to generate carbonium ions (e.g., C2H5+, C3H7+ and C4H9+). Subsequently, all of them enter into the intersection channels to induce the occurrence of bimolecular reaction. Such a process is conducive to the formation of ethylene. These insights can help to clarify the catalytic behavior of regional framework acid sites in ZSM-5 channels and then provide an effective approach to design efficient TCO catalysts.