Quantification of acidic sites of nanoscopic hydroxylated magnesium fluorides by FTIR and 15N MAS NMR spectroscopy

Felix Hemmann; Iker Agirrezabal-Telleria; Christian Jaeger; Erhard Kemnitz

doi:10.1039/C5RA15116C

Quantification of acidic sites of nanoscopic hydroxylated magnesium fluorides by FTIR and ¹⁵N MAS NMR spectroscopy†

Felix Hemmann,^ab Iker Agirrezabal-Telleria,^c Christian Jaeger^b and Erhard Kemnitz*^a

* Corresponding authors

^a Humboldt-Universität zu Berlin, Department of Chemistry, Brook – Taylor – Str. 2, D-12489 Berlin, Germany
E-mail: felix.hemmann@bam.de, erhard.kemnitz@chemie.hu-berlin.de

^b BAM Federal Institute for Materials Research and Testing, Division 1, Richard Willstaetter Str. 11, D-12489 Berlin, Germany
E-mail: christian.jaeger@bam.de

^c Department of Chemical and Environmental Engineering, Engineering School of the University of the Basque Country (UPV/EHU), Alameda Urquijo s/n, 48013 Bilbao, Spain
E-mail: iker.aguirrezabal@ehu.es

Abstract

Lewis and Brønsted sites were quantified in a series of weak acidic hydroxylated magnesium fluorides by Fourier transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance spectroscopy (NMR) with pyridine as probe molecule. Molar extinction coefficients, which are necessary for quantitative FTIR measurements, were calculated by an easy approach. It utilizes the fact that both signals, used for the quantification by FTIR, are caused by the same deformation vibration mode of pyridine. Comparison of quantitative FTIR experiments and quantification by NMR shows that concentrations of acidic sites determined by FTIR spectroscopy have to be interpreted with caution. Furthermore, it is shown that the transfer of molar extinction coefficients from one catalyst to another may lead to wrong results. Molar extinction coefficients and concentrations of acidic sites determined by FTIR spectroscopy are affected by grinding and probably the particle size of the sample. High temperature during FTIR experiments has further impact on the quantification results.

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DOI: https://doi.org/10.1039/C5RA15116C
Article type: Paper
Submitted: 29 Jul 2015
Accepted: 15 Oct 2015
First published: 15 Oct 2015
This article is Open Access

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RSC Adv., 2015,5, 89659-89668

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Quantification of acidic sites of nanoscopic hydroxylated magnesium fluorides by FTIR and ¹⁵N MAS NMR spectroscopy

F. Hemmann, I. Agirrezabal-Telleria, C. Jaeger and E. Kemnitz, RSC Adv., 2015, 5, 89659 DOI: 10.1039/C5RA15116C

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