Control of the Al Distribution in the Framework of ZSM-5 Zeolite and Its Evaluation by Solid-State NMR Technique and Catalytic Properties

Abstract

The effects of the organic structure-directing agents (OSDAs) and Na cations for the synthesis of ZSM-5 on the location of Al atom in the framework as well as the acidic and catalytic properties were investigated. To achieve these purposes, ZSM-5 zeolites were synthesized by using four kinds of OSDAs including tetrapropylammonium hydroxide cations, dipropylamine, cyclohexylamine, and hexamethylenimine with or without Na cations. In situ FT-IR spectroscopy using CO as probe molecule was applied to the evaluation of the acid property of the ZSM-5 zeolites. The location of Al atoms was examined by high resolution 27Al MAS and MQMAS NMR techniques. The constraint index (CI) has also been used to estimate the distribution of acid sites in the micropores. The location of acid sites was investigated based on the difference in the transition-state shape-selectivity through the cracking of n-hexane and 3-methylpentane. Furthermore, the cracking of various types of paraffins and the conversion of aromatic compounds were conducted to clarify the acid site distributions.