Quantification of enhanced acid site accessibility in hierarchical zeolites – The accessibility index
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- 作者：Fré ; dé ; ric Thibault-Starzyk ; Irina Stan ; Sò ; nia Abelló ; Adriana Bonilla ; Karine Thomas ; Christian Fern ; ez ; Jean-Pierre Gilson ; Javier Pé ; rez-Ramí ; rez
- 关键词：Accessibility index ; Hierarchical zeolites ; Desilication ; Mesoporous crystals ; Infrared spectroscopy ; Alkylpyridines ; Catalyst effectiveness
- 刊名：Journal of Catalysis
- 出版年：2009
- 出版时间：15 May 2009
- 年：2009
- 卷：264
- 期：1
- 页码：11-14
- 全文大小：324 K
文摘
An accessibility index (ACI) was derived from infrared spectroscopy of substituted alkylpyridines with different size (pyridine: 0.57 nm, 2,6-lutidine: 0.67 nm, and 2,4,6-collidine: 0.74 nm) over hierarchical porous ZSM-5 crystals. The samples were prepared by selective silicon extraction of a commercial sample in NaOH (desilication), and they contained different degrees of intracrystalline mesoporosity. Our results demonstrate the enhanced accessibility of Brønsted acid sites in the hierarchical zeolites. For example, a relatively bulky molecule such as collidine, which probes practically no acid site of the parent medium-pore MFI structure, can access up to 40 % of the acid sites in the mesoporous sample. The ACI is a powerful tool to standardize acid site accessibility in zeolites, and can be used to rank the effectiveness of synthetic strategies to prepare hierarchical zeolites.