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Probing the acid sites of zeolites with pyridine: quantitative AGIR measurements of the molar absorption coefficients

Zholobenko

Probing the acid sites of zeolites with pyridine: quantitative AGIR measurements of the molar absorption coefficients Thumbnail


Authors

Zholobenko



Abstract

This study presents a detailed methodology, which combines high-precision thermogravimetry and FTIR spectroscopy, aiming to establish the most accurate and reliable means of measuring the molar absorption coefficients of adsorbed species. As the integrated molar absorption coefficients of Py complexes with Brønsted and Lewis acid sites, ?(Py-B) and ?(Py-L), are determined and the validity of the Beer-Lambert-Bouguer law for IR characterisation of solid acids is demonstrated, this work is setting a benchmark for the quantitative acidity measurements in zeolites and related materials. The following values of ?(Py-B) have been obtained at 150°C (band at ~1545 cm-1): 1.09±0.08 cm µmol-1 for ZSM-5; 1.12±0.16 cm µmol-1 for BEA; 1.29±0.04 cm µmol-1 18 for MOR and 1.54±0.15 cm µmol-1 for FAU. The value of ?(Py-L) (band at ~1455 cm-1 19 , which refers to different cations) measured at the same temperature is 1.71±0.1 cm µmol-1 20 . Values of ?(Py-B) depend on the zeolite structure, in contrast to that for ?(Py-L). Clear correlations are presented between the temperature of the FTIR measurements and ? values for Py complexes and other species, which decrease by ~10% as the temperature increases by 100oC. In addition, the effects of key experimental procedures, instrumentation design and sample preparation are established and quantified.

Acceptance Date Mar 4, 2020
Publication Date May 1, 2020
Publicly Available Date Mar 28, 2024
Journal Journal of Catalysis
Print ISSN 0021-9517
Publisher Elsevier
Pages 52-60
DOI https://doi.org/10.1016/j.jcat.2020.03.003
Keywords zeolites; acid sites; FTIR; pyridine; molar absorption coefficients
Publisher URL https://doi.org/10.1016/j.jcat.2020.03.003

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