Assessing the acidity of high silica chabazite H-SSZ-13 by FTIR using CO as molecular probe: Comparison with H-SAPO-34.

Détails

ID Serval
serval:BIB_79DC53445B89
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Titre
Assessing the acidity of high silica chabazite H-SSZ-13 by FTIR using CO as molecular probe: Comparison with H-SAPO-34.
Périodique
Journal of Physical Chemistry. B
Auteur(s)
Bordiga S., Regli L., Cocina D., Lamberti C., Bjørgen M., Lillerud K.P.
ISSN
1520-6106
Statut éditorial
Publié
Date de publication
02/2005
Volume
109
Numéro
7
Pages
2779-2784
Langue
anglais
Résumé
Zeolitic materials based on the chabazite topology, such as H-SAPO-34, possess unique shape-selectivity properties for converting methanol into light olefins. In addition to the topology, zeolite acidity is inherently linked to catalyst activity and selectivity. The acidic properties of high silica chabazite (H-SSZ-13) have attracted much attention in the past decade because the material represents an idealized model system having one acidic site per cage. Conclusions drawn so far have essentially been founded on quantum chemical methods. An experimentally based benchmark of the acidity of H-SSZ-13 has hitherto not been available. In this work, transmission FTIR spectroscopy provides a description of the different acidic sites of H-SSZ-13 by using CO as molecular probe at 70 K. The results demonstrate that H-SSZ-13 is a strongly Brønsted acidic material, essentially having two distinct families of acidic sites. In contrast to numerous preceding reports, we find it fundamental to consider proton distributions among all four possible sites, and do not delimit the interpretations to only two sites. The present data consistently suggest the most abundant family of protons to have three members being located on different crystalline positions on the eight-membered-ring window giving access to the chabazite cage. Consequently, these protons are exposed to two neighboring cages. The second, and less abundant family, is constituted by only one site that is situated on the six-membered ring defining the top/bottom of the barrel-shaped chabazite cage. This proton is therefore only exposed to one cage and requires a higher CO pressure to form adducts. Toward CO, both families of sites possess the same acidity. Parallel experiments were also carried out for the isostructural and commercially important H-SAPO-34 having an equal density of acidic sites. This is the first attempt to directly compare, on an experimental basis, the acidity of these two materials.
Pubmed
Web of science
Création de la notice
25/01/2008 14:10
Dernière modification de la notice
03/03/2018 18:32
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