Evaluation of Zeolite Acidity by 31P MAS NMR Spectroscopy of Adsorbed Phosphine Oxides: Quantitative or Not?

Zasukhin, D.S.; Kasyanov, I.A.; Kolyagin, Y.G.; Bulygina, A.I.; Kharas, K.C.; Ivanova, I.I.

Авторы: Zasukhin Dmitry S., Kasyanov Ivan A., Kolyagin Yury G., Bulygina Anna I., Kharas Karl C., Ivanova Irina I.
Журнал: ACS Omega
Том: 7
Номер: 14
Год издания: 2022
Первая страница: 12318
Последняя страница: 12328
DOI: 10.1021/acsomega.2c00804
Аннотация: 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy of adsorbed alkyl-substitutedphosphine oxides has witnessed tremendous progress during thelast years and has become one of the most informative andsensitive methods of zeolite acidity investigation. However,quantitative evaluation of the number of sites is still a challenge.This study clarifies the main origin of errors occurring duringNMR experiments, introduces the appropriate standards (bothinternal and external), and determines the relaxation parametersand the conditions for the acquisition and integration of spectra.As a result, a methodology for the quantitative measurement of thecontent of Brønsted and Lewis sites and the amount of internaland external silanol groups is established. The application of probe molecules of different sizes (namely, trimethylphosphine oxide(TMPO), tri-n-butylphosphine oxide (TBPO), and tri-n-octylphosphine oxide (TOPO)) is shown to be a good tool fordistinguishing between the active sites inside the zeolite pores, mesopores, and on the outer crystal surface. The methodologyproposed is verified on BEA zeolites different in composition, texture, and morphology.
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Evaluation of Zeolite Acidity by 31P MAS NMR Spectroscopy of Adsorbed Phosphine Oxides: Quantitative or Not?статья Исследовательская статья

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