HIGH-SURFACE-AREA NAFION RESIN SILICA NANOCOMPOSITES - A NEW CLASS OFSOLID ACID CATALYST/

Nafion resin, a perfluorinated ion-exchange polymer, has been used as a heterogeneous strong acid catalyst for a range of reactions; however , in nonpolar solvents or for gas phase reactions the activity is limi ted due to the extremely low surface area of the polymer beads (<0.02 m(2) g(-1)). In this paper we describe a novel nanocomposite of Nafion resin, in which small (20-60 nm diameter) Nafion resin particles are entrapped within a porous silica network. This material combines the e xcellent solid acid catalyst properties of Nafion resin with the desir able porous support characteristics of silica. BET surface area is typ ically in the range of 150-500 m(2) g(-1) for the composite. Assuming the Nafion resin particles are dense spheres we estimate the effective surface area of the Nafion resin alone to be in the range of 153 (20 nm spheres) to 50 (60 nm spheres) m(2) g(-1). This new material has be en developed using an in situ sol-gel technique wherein solutions of N afion resin are mixed with soluble silicon sources to form a gel, whic h is dried to a clear hard glass-like material. These new porous nanoc omposites offer the potential for significantly enhanced activity due to the increased accessibility of the Nafion resin-based acid sites. W e show examples of catalytic reactions in which the activity per unit weight of Nafion resin has been found to be at least 100 times higher in the composite than the pure polymer.