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Title: | Elucidating the Nature of the External Acid Sites of ZSM-5 Zeolites Using NMR Probe Molecules |
Author: | Bornes, Carlos Stosic, Dusan Geraldes, Carlos F. G. C. Mintova, Svetlana Rocha, João Mafra, Luís |
Keywords: | Magnetic Resonance Spectroscopy Magnetic Resonance Imaging Acids Zeolites |
Issue Date: | 16-Nov-2022 |
Publisher: | Wiley-Blackwell |
Abstract: | The identification of acid and nonacid species at the external surface of zeolites remains a major challenge, in contrast to the extensively-studied internal acid sites. Here, it is shown that the synthesis of zeolite ZSM-5 samples with distinct particle sizes, combined with solid-state NMR and computational studies of trimethylphosphine oxide (TMPO) adsorption, provides insight into the chemical species on the external surface of the zeolite crystals. 1 H-31 P HETCOR NMR spectra of TMPO-loaded zeolites exhibit a broad correlation peak at δP ∼35-55 ppm and δH ∼5-12 ppm assigned to external SiOH species. Pore-mouth Brønsted acid sites exhibit 31 P and 1 H NMR resonances and adsorption energies close to those reported for internal acid sites interacting with TMPO. The presence of an external tricoordinate Al-Lewis site interacting strongly with TMPO is suggested, resulting in 31 P resonances that overlap with the peaks usually ascribed to the interaction of TMPO with Brønsted sites. |
Peer review: | yes |
URI: | http://hdl.handle.net/10773/35937 |
DOI: | 10.1002/chem.202201795 |
ISSN: | 0947-6539 |
Appears in Collections: | CICECO - Artigos DQ - Artigos |
Files in This Item:
File | Description | Size | Format | |
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Chemistry A European J - 2022 - Bornes - Elucidating the Nature of the External Acid Sites of ZSM%E2%80%905 Zeolites Using NMR.pdf | 1.68 MB | Adobe PDF |
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