Document Detail

Impacts of Composition and Post-Treatment on the Brønsted Acidity of Steam-Treated Faujasite: Insights from FTIR Spectroscopy.
MedLine Citation:
PMID:  23001830     Owner:  NLM     Status:  Publisher    
A detailed FTIR study of the effects of steaming and acid leaching on protonated Y faujasite (FAU) and EMT zeolites is provided and the results are thoroughly analysed. In particular, emphasis is placed on the Brønsted acidic evolution and acidic strength measurements for a large series of as-modified zeolites using CO as a sensitive probe to distinguish various protonic sites. While an increase of acidity for framework OH groups is observed during the strengthening of dealumination for both FAU and EMT series, the steaming process also generates a large variety of additional Brønsted acidic groups. Regarding acidic strength, these heterogeneous OH groups are sensitive to post-treatments and their existence strongly depends on the initial composition of the zeolites. The presence of residual Na(+) cations in the starting materials induces dramatic Brønsted acidic changes after steaming. As a result, steamed zeolites that initially contain traces of sodium possess unusual acidic Brønsted groups with low acidity. This result contradicts the trend generally observed with framework OH groups, for which steaming results in an increase of Brønsted acidic strength. The study reveals that the situation is indeed more complex, as some compositions and post-treatments strongly influence the Brønsted acidity of as-steamed zeolites both in their nature and their corresponding acidic strength. By linking these IR-compiled features to the as-exposed modifications, a large acidity scale better suited to characterizing catalysts having Brønsted acidity expanding from lowest to highest strength is proposed.
Olivier Cairon
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-9-23
Journal Detail:
Title:  Chemphyschem : a European journal of chemical physics and physical chemistry     Volume:  -     ISSN:  1439-7641     ISO Abbreviation:  Chemphyschem     Publication Date:  2012 Sep 
Date Detail:
Created Date:  2012-9-24     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100954211     Medline TA:  Chemphyschem     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
UFR Sciences & Techniques, 64053 Pau Cedex 9 (France).
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