Elucidating the Nature of the External Acid Sites of ZSM-5 Zeolites Using NMR Probe Molecules.
Chemistry
; 28(64): e202201795, 2022 Nov 16.
Article
in En
| MEDLINE
| ID: mdl-35943080
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 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.
Key words
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Zeolites
Language:
En
Journal:
Chemistry
Journal subject:
QUIMICA
Year:
2022
Type:
Article
Affiliation country:
Portugal