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An accessibility index (ACI) was derived from infrared spectroscopy of substituted alkylpyridines with different size (pyridine: 0.57nm, 2,6-lutidine: 0.67nm, and 2,4,6-collidine: 0.74nm) 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. [Copyright &y& Elsevier]

Abstract: The preparation of mesoporous mordenite zeolite and its subsequent application in the liquid-phase alkylation of benzene with ethylene is discussed. Mesoporous mordenite was obtained by controlled silicon extraction on alkaline treatment of successfully synthesized high-silica mordenite zeolites with molar Si/Al ratios in the range of 20–30. Besides substantial mesoporosity development, the combined microporous and mesoporous zeolites show preserved Brønsted acidic properties, which are highly attractive when acid-catalyzed reactions are targeted. Catalytic testing of the mesoporous mordenite found superior performance in benzene alkylation due to the unique interplay between improved physical transport in the shortened micropores and the preserved high density of acid sites. [Copyright &y& Elsevier]