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Optimising catalytic properties of supported sulfonic acid catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
42867 45944 2009 6 PDF Available
Title
Optimising catalytic properties of supported sulfonic acid catalysts
Abstract

Siliceous mesoporous molecular sieves (SBA-15) have been functionalised with propylsulfonic acid groups by both co-condensing 3-mercaptopropyltrimethoxysilane with the solid at the synthesis (sol–gel) stage and by grafting the same compound to pre-prepared SBA-15, followed, in both cases, by oxidation to sulfonic acid. The acidic and catalytic properties of the supported sulfonic acids prepared in the two ways have been compared, using ammonia adsorption calorimetry and the benzylation reaction between benzyl alcohol and toluene. Using a combination of X-ray photoelectron spectroscopy and other analytical techniques, the level of functionalisation and the extent of subsequent oxidation of tethered thiol to sulfonic acid, both in the bulk and close to the surface of SBA-15 particles, have been assessed. The research shows that the co-condensing route leads to higher levels of functionalisation than the grafting route. The extent of oxidation of added thiol to acid groups is similar using the two routes, about 70% near the surface and only 50% in the bulk. Comparison is made with polymer supported sulfonic acid catalysts, Amberlysts 15 and 35, and Nafion. Nafion shows the highest acid strength and the highest specific catalytic activity of all materials studied. Amongst the other materials, average acid strengths are broadly similar but there appears to be a relationship between the concentration of acid sites on the catalysts and their specific activity in the benzylation reaction. A model is proposed to explain this, in which clustering of sulfonic acid groups, even to a small extent, leads to disproportionately enhanced catalytic activity.

Graphical abstractSiliceous SBA-15 supported sulfonic acids were prepared by grafting and co-condensation routes and their surface acidities and catalytic activities compared. By including polystyrene sulfonic acids and Nafion in the study, conclusions have been reached about the importance of interactions between neighbouring acid groups in generating high acid strengths and catalytic activities.Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
SBA-15; Solid acid catalysts; Flow adsorption calorimetry; Catalytic activity; Structure–activity correlation
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 364, Issues 1–2, 31 July 2009, Pages 95–100
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