The influence of liquid reaction media on acidities and activities of solid acid catalysts
Novel H+ -sulfori"ated poly( styrene-co-divinylbenzene) ion-exchange resins
have been prepared with· higher acid strength and higher thermal stabilities
than conventionai ion-exchange resins. An objective of the study has been to
increase the understanding of the relationships between resins structures,
acidities and acid catalytic activities in aqueous and non-aqueous media.
Some related materials, supported sulfonic acid catalysts, have been
prepared using HMS (hexagonal mesoporous silicas) and SBA 15 as
supports. These catalysts were characterised in terms of surface area and
pore size distribution from nitrogen adsorption, powder X-ray diffraction,
cation exchange capacity, thermogravimetric analysis and FT-Raman
spectroscopy. These functionalised inorganic materials have been compared
with their organic counterparts to improve the understanding of these
Both of these ranges of catalysts, with varying level of sulfonation, have been
characterised by ammonia adsorption microcalorimetry in the absence of
solvent. The resulting molar enthalpies of ammonia adsorption have been
interpreted in terms of the relative strength of acid sites.
The same catalysts have also been neutralised in a titration microcalorimeter
(TITRYS) in which the materials have been held under a solvent (water,
acetonitrile, cyclohexane) and a base probe compound titrated into the
sample cell in the same solvent. Molar enthalpies of neutralisation measured
for thes'e solid acid catalysts in this way have been compared with molar
enthalpies of neutralisc:!ion for similar acid groups (sulfonic acids) in
homogeneous solutions. The resulting molar enthalpies of neutralisation in
non-aqueous solvents have been interpreted in terms of the relative strength
of acid sites.
In addition, FT-Raman spectroscopy has been used to study the sulfonic acid
groups in the resin gels and comparison made with similar acid groups in
homogeneous aqueous solutions.
These in turn have been compared with catalytic data measured for the
sulfonated catalysts in three liquid phase reactions.
Variation in measured acidity (with and without) solvent, catalytic activities
have been interpreted in terms of structural features of the catalysts and their
interaction with solvents.