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

Lewis and Broensted 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 fo...

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Bibliographic Details
Published in:RSC advances 2015-10, Vol.5 (109), p.89659-89668
Main Authors: Hemmann, Felix, Agirrezabal-Telleria, Iker, Jaeger, Christian, Kemnitz, Erhard
Format: Article
Language:English
Subjects:
Extinction
Fourier transforms
Infrared spectroscopy
Magnesium fluorides
Nuclear magnetic resonance
Pyridines
Spectroscopy
Vibration mode
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Summary:Lewis and Broensted 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.
ISSN:2046-2069
DOI:10.1039/c5ra15116c