The understanding of location and accessibility of zeolite acid sites is a key issue in heterogeneous catalysis. This paper provides a brief overview of Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) characterisation of acidity in zeolites based
on the application of test molecules with a diverse range of basicity and kinetic diameters. Many zeolites, including ZSM-5 and BEA, have been characterised by monitoring the interaction between the zeolite acid sites and test molecules, such as 1,3,5-triisopropylbenzene, pyridine and alkylpyridines,
to probe the location, accessibility and strength of the Brønsted acid sites. 1,3,5-triisopropylbenzene can be used to distinguish Brønsted acid sites located on the external and internal surface in most medium and large pore channel zeolites. Brønsted acid sites on the
external surface of medium pore zeolites can also be quantified using 2,6-di-tert-butyl-pyridine and 2,4,6-trimethylpyridine. It is concluded that using a combination of probe molecules, including co-adsorption experiments, affords differentiation between acid sites located in channels
and cavities of different sizes and on the external and internal surfaces of various zeolitic structures.
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Document Type: Research Article
July 1, 2018
This article was made available online on June 11, 2018 as a Fast Track article with title: "Accessibility and location of acid sites in zeolites as probed by FTIR and MAS-NMR ".
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