The Influence of Solvent on the Acidity and Activity of Supported Sulfonic Acid Catalysts

Abstract

The acid strengths and catalytic activities of sulfonic acids supported on polystyrene resins and ordered mesoporous HMS and SBA-15 silicas are compared. Acid strengths are measured by acid-base titration calorimetry in terms of the molar enthalpies of neutralisation with either NaOH or n-butylamine in water, acetonitrile and cyclohexane. Catalytic activities (turnover numbers) are reported in model reactions in water, 1,2-dichlorobenzene and anisole, and compared with acid strengths. In water, sulfonated resins are both stronger acids and more active catalysts than sulfonated silicas. Catalytic activities in water correlate well with these measured acid strengths. In acetonitrile the order of acid strengths is reversed and the sulfonated silicas are the stronger acids. Catalytic measurements in 1,2-dichlorobenzene, a similar dipolar aprotic solvent, show the same reversed order of activities. In the non-polar solvent cyclohexane (where only macroporous sulfonated resins show measurable acidity) the sulfonated silicas are again the stronger acids but by a larger margin. Catalytic activities in anisole, which is also only very weakly solvating towards sulfonic acid groups, show a similar trend. The results illustrate the role of the solvent in controlling the acid strength of solid acid catalysts, and the importance of taking this into account when designing acid catalysts for liquid phase processes.

Double-bond isomerization of hexadecenes with solid acid catalysts

“…By this same hypothesis, alkyl-tethered sulfonated silicas should be more active on a site basis for any Brønsted acid-catalyzed reaction than the more rigid sulfonated PS-DVBs with one -SO 3 H per ring. This has been observed -significantly so -in previous studies of esterification catalysis [39], and in both ketone acetalization and amine acylation [40]. We conclude that the enhanced activities of both SAC-13 relative to the alumina-supported Nafions, and of the oversulfonated resins relative to the other PS-DVBs result from better acid site cooperativity.…”

Direct synthesis of acid–base bifunctionalized hexagonal mesoporous silica and its catalytic activity in cascade reactions

“…Meanwhile, organic acid center in bifuntionalized materials is mainly benzenesulfonic acid because 2-(4-chlorosulfonylphenyl) ethyl-trimethoxysilane can easily hydrolyze to corresponding acid [15][16][17]19,20]. In contrast, 3-mercaptopropyltrimethoxysilane is a more prevalent organicsilane to create acid center [25][26][27]. Reports about catalysts containing both anchored propanesulfonic acid and aminopropyl are rare because amino as basic centers can also be 0021-9797/$ -see front matter Ó 2010 Elsevier Inc. All rights reserved.…”

Optimization of the preparation method of HSO3-functionalized MCM-41 solid catalysts

“…the co-condensation route [7][8][9][10][11][12][13][14][15][16], and (ii) post-synthesis anchoring of the acid moiety precursors onto purely siliceous materials after surfactant removal, i.e. the grafting method [17][18][19][20]. Materials obtained by using the co-condensation route possess a higher number of acid centers and a remarkable performance in acid catalyzed reactions such as direct esterification of fatty acids with glycerol to selectively obtain the corresponding monoesters [21,22].…”