Nafion resin-silica nanocomposite solid acid catalysts. Microstructure-processing-property correlations

We have developed a new class of solid acid catalyst, a Nafion resin/silica nanocomposite, which effectively catalyzes a wide range of industrially important reactions. These include olefin isomerizations, alkylations, acylations, oligomerizations, the Fries reaction, esterifications and benzylations. We have found that the catalytic activity of these materials is dependent upon the synthetic conditions. The catalytic activity is related to the extent of dispersion of the Nafion resin acid groups within the porous silica framework. The use of an in situ sol-gel technique is preferred over infiltration of a pre-formed support with a Nafion solution. Here we show how we can use solid state NMR, electron microscopy and temperature programmed desorption to elucidate the chemical environment and dispersion of the acid sites. We also show how the microstructure may be tailored depending upon the synthetic conditions. This is a rare example of tuning catalyst activity for particular reactions. In the case of alkylations (such as formation of linear alkyl benzenes), transalkylation and acylation chemistry, the activities are increased several fold using a catalyst in which the Nafion resin is slightly aggregated. A highly dispersed form of the Nafion resin within the silica is preferred for dimerization chemistry. In the case of olefin isomerization chemistry, variations in the Nafion resin dispersion have little effect upon catalytic activity. A correlation of microstructure-processing-properties is described.