Chapter 6 - Nanoscaled Metal Fluorides in Heterogeneous Catalysis

Abstract

This chapter focuses on nanoscopic metal fluorides and hydroxide fluorides prepared via a recently explored fluorolytic sol–gel synthesis approach. Metal fluoride phases obtained via this route exhibit exciting catalytic properties making them distinctly different as compared with their classically prepared homologues. As a result, very strong solid Lewis acids are available that give access to new catalytic reactions with sometimes unexpectedly high conversion degrees and selectivity. Even more interestingly, metal hydroxide fluorides can be obtained via this synthesis route, being not at all accessible via any other approach. The fluorolytic sol–gel synthesis allows an adjustment of the hydroxide to fluoride ratio over a wide range. Thus, biacidic (Brønsted and Lewis) solids with tunable Lewis to Brønsted acidity are available that show interesting catalytic properties in a variety of different reactions. Finally, these new nanometal fluorides, due to their very high surface areas and distinct acidic properties, are excellent candidates as support for many novel metal-catalyzed reactions, showing surprising synergistic effects. This chapter will briefly outline the synthesis approach of the fluorolytic sol–gel route with some mechanistic aspects, will present characteristic bulk and surface properties, and will give several examples of novel catalytic applications of nanoscaled metal fluorides in purely Lewis acid and in biacidic catalyzed reactions, and will also exemplarily show the potential of these new materials as supports for heterogeneous catalytic reactions.