Acid strengths and catalytic activities of sulfonic acid on polymeric and silica supports

✍ Scribed by P.F. Siril; A.D. Davison; J.K. Randhawa; D.R. Brown

• Publisher: Elsevier Science
• Year: 2007
• Tongue: English
• Weight: 174 KB
• Volume: 267
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/j.molcata.2006.11.022

✦ Synopsis

The acidic and catalytic properties of sulfonic acids supported on polystyrene, on silica (via propyl and phenyl tethers) and on a fluorinated hydrocarbon polymer (Nafion) are compared. Surface acidities are characterised using ammonia adsorption calorimetry under flow conditions in which pulses of ammonia are introduced to the sample from a flowing carrier stream. The extent of adsorption and molar enthalpies of ammonia adsorption ( H ads • ) are interpreted in terms of the abundance, accessibility and strength of surface acid sites. Catalytic activities are measured for the isomerisation of ␣-pinene. The Nafion catalysts show the highest H ads • (NH 3 ) and the highest catalytic activities. Although both silicasupported and polystyrene-supported sulfonic acids show lower specific activities and lower H ads • (NH 3 ) values, the correlation between activity and H ads • (NH 3 ) is relatively poor for these supported forms of the acid. It appears that while H ads • (NH 3 ) is certainly sensitive to the strength of acid groups on which ammonia is adsorbed, it can only be used to compare acid strengths in a meaningful way for structurally similar catalysts.