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IR studies of OH groups in mesoporous aluminosilicates

Paper ID Volume ID Publish Year Pages File Format Full-Text
43884 45993 2006 6 PDF Available
Title
IR studies of OH groups in mesoporous aluminosilicates
Abstract

The properties of acidic hydroxyl groups and Lewis acid sites in amorphous mesoporous aluminosilicates was followed by quantitative IR studies of ammonia adsorption and by low temperature studies of CO adsorption. We studied aluminosilicates synthesized by three methods: via atrane complexes, by grafting aluminium onto the siliceous material (HMCM-48) and in aqueous solution following a typical synthesis procedure (HMCM-41). IR spectra of OH groups showed weak but well seen band of Si–(OH)–Al groups at 3600–3610 cm−1. The post-synthesis grafting of Al into MCM-48 was found to be the most effective way to produce mesoporous material with large content of Brønsted acid sites. IR studies have shown that the stoichiometry of dehydroxylation of the amorphous mesoporous materials was different than for zeolites: in mesoporous materials one Brønsted site lost created one Lewis acid site. IR experiments of CO sorption evidenced that generally two kinds of Si–(OH)–Al groups exist in mesoporous aluminosilicates: weakly acidic ones of ΔνOH⋯CO ≈ 160 cm−1 (similar to that in zeolite NaHX), present in all the materials, hydroxyls of moderate acidity of ΔνOH⋯CO ≈ 200 cm−1 (acid strength intermediate between that in zeolites NaHX and NaHY) present in HMCM-41 and HMCM-48, or hydroxyls of high acidity of ΔνOH⋯CO ≈ 300 cm−1 (similar to that in highly siliceous zeolite HZSM-5) present in aluminoslicate prepared via atrane complexes method. This method of synthesis was found to be the most effective in preparation of mesoporous aluminosilicates with the strongest Brønsted acid sites. The weakly acidic hydroxyls in mesoporous aluminosilicates are very prone to dehydroxylation, they are lost at as low temperature as 800 K, hydroxyls of moderate, or high acidity are resistant to dehydroxylation and behave like zeolitic OH groups.

Keywords
Acidity; OH groups; Mesoporous materials; Dehydroxylation; IR spectroscopy
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IR studies of OH groups in mesoporous aluminosilicates
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 302, Issue 1, 21 March 2006, Pages 104–109
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us