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  Proton Mobility, Intrinsic Acid Strength, and Acid Site Location in Zeolites Revealed by Varying Temperature Infrared Spectroscopy and Density Functional Theory Studies

Losch, P., Joshi, H. R., Vozniuk, O., Grünert, A., Ochoa-Hernández, C., Jabraoui, H., et al. (2018). Proton Mobility, Intrinsic Acid Strength, and Acid Site Location in Zeolites Revealed by Varying Temperature Infrared Spectroscopy and Density Functional Theory Studies. Journal of the American Chemical Society, 140(50), 17790-17799. doi:10.1021/jacs.8b11588.

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Losch, Pit1, Autor           
Joshi, Hrishikesh R.2, Autor           
Vozniuk, Olena2, Autor           
Grünert, Anna2, Autor           
Ochoa-Hernández, Cristina2, Autor           
Jabraoui, Hicham3, Autor
Badawi, Michael3, Autor
Schmidt, Wolfgang1, Autor           
Affiliations:
1Research Group Schmidt, Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_1445618              
2Research Department Schüth, Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_1445589              
3Laboratoire Physique et Chimie Théoriques, UMR 7019 CNRS-Université de Lorraine, Saint Avold 57500, France, ou_persistent22              

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 Zusammenfassung: The intrinsic Brønsted acid strength in solid acids relates to the energy required to separate a proton from a conjugate base, for example a negatively charged zeolite framework. The reliable characterization of zeolites’ intrinsic acidity is fundamental to the understanding of acid catalysis and setting in relation solid Brønsted acids with their activity and selectivity. Here, we report an infrared spectroscopic study with partial isotopic deuterium exchange of a series of 15 different acidic aluminosilicate materials, including ZSM-5 zeolites with very few defects. Varying Temperature Infrared spectroscopy (VTIR) permitted estimating activation energies for proton diffusion. Two different proton transfer mechanisms have been distinguished for two different temperature ranges. Si-rich zeolites appeared to be promising proton-transfer materials (Eact. < 40 kJ mol–1) at temperatures above 150 °C (423 K). Further, a linear bathochromic shift of the Si–(OD)–Al stretching vibration as a function of temperature was observed. It can be assumed that this red-shift is related to the intrinsic O–(H/D) bond strength. This observation allowed the extrapolation and estimation of precise v(O–D)@0 K values, which could be attributed to distinct crystallographic locations through Density Functional Theory (DFT) calculations. The developed method was used to reliably determine the likelihood of the position of a proton in ZSM-5 zeolites under catalytically relevant conditions (T > 423 K), which has so far never been achieved by any other technique.

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Sprache(n): eng - English
 Datum: 2018-11-062018-11-292018-12-19
 Publikationsstatus: Erschienen
 Seiten: 10
 Ort, Verlag, Ausgabe: -
 Inhaltsverzeichnis: -
 Art der Begutachtung: Expertenbegutachtung
 Identifikatoren: DOI: 10.1021/jacs.8b11588
 Art des Abschluß: -

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Titel: Journal of the American Chemical Society
  Andere : J. Am. Chem. Soc.
  Kurztitel : JACS
Genre der Quelle: Zeitschrift
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Ort, Verlag, Ausgabe: Washington, DC : American Chemical Society
Seiten: - Band / Heft: 140 (50) Artikelnummer: - Start- / Endseite: 17790 - 17799 Identifikator: ISSN: 0002-7863
CoNE: https://pure.mpg.de/cone/journals/resource/954925376870