Nafion-Silica Nanocomposites: A New Generation of Water-Tolerant Solid Acids of High Efficiency—An Update

The methods to prepare Nafion materials with significantly improved specific activities, their characterization and applications as useful and efficient catalysts are summarized. The sol-gel technique used most widely, covalent anchoring of the sulfonic acid group to the surface via a perfluoroalkane tether via post-synthesis modification, impregnation of high-porosity spinodal silica and mesoporous silica materials, and mechanochemistry all allow the formation of Nafion materials with enhanced accessibility of the active sites and, consequently, improved catalytic properties can be experienced. The review includes and discusses the use of related immobilized fluoroalkanesulfonic acid preparations. The transformations induced by these solid acids including Friedel-Crafts and related reactions, various transformations of alkenes, alcohols, and carbonyl compounds, protective group chemistry, chemistry of carbohydrates and heterocycles, oxidations, and a few examples of non-catalytic applications are treated in detail.