Elucidating the Nature of the External Acid Sites of ZSM-5 Zeolites Using NMR Probe Molecules.
Chemistry
; 28(64): e202201795, 2022 Nov 16.
Article
en En
| MEDLINE
| ID: mdl-35943080
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 â¼35-55â
ppm and δH â¼5-12â
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.
Palabras clave
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Zeolitas
Idioma:
En
Revista:
Chemistry
Asunto de la revista:
QUIMICA
Año:
2022
Tipo del documento:
Article
País de afiliación:
Portugal
Pais de publicación:
Alemania