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

摘要

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 limited 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 excellent solid acid catalyst properties of Nafion resin with the desirable porous support characteristics of silica. BET surface area is typically 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 been developed using an in situ sol-gel technique wherein solutions of Nafion resin are mixed with soluble silicon sources to form a gel, which is dried to a clear hard glass-like material. These new porous nanocomposites offer the potential for significantly enhanced activity due to the increased accessibility of the Nafion resin-based acid sites. We 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.