Metal fluorides, heterogeneous

Li H, Balaya P, Maier J. Li-storage via heterogeneous reaction in selected binary metal fluorides and oxides. J Electrochem Soc. 2004 151(ll) A1878-85. 

In this chapter, recent advances in our understanding of catalytic fluorination under heterogeneous conditions are surveyed from the standpoint of catalyst properties, including developments based on the use of mixed metal fluorides having different structural types, and reaction mechanisms. Much of the newer work has been the result of the need to replace chlorofluorocarbons (CFCs) by alternatives, hydrofluorocarbons (HFCs) or, more controversially, hydrochlorofluorocarbons (HCFCs), following adoption of the Montreal and successor Protocols [2,3]. Where relevant, aspects of catalytic hydrogenolysis, where fluorides have been used as replacement supports in the conventional palladium/carbon catalysts, and isomerization reactions are included. 

By the direct fluorination with elemental fluorine, it is still difficult to prepare pure compounds C6oF.v and C70F of specific fluorine content because the reaction between fluorine gas and solid state C6o and C70 proceeds under heterogeneous conditions and, therefore, lacks control. Attempts to prepare stoichiometrically pure compounds have become successful using solid phase reactions between fullerenes and metal fluorides. These are described in the next section. It has been unsuccessful so far, but efforts are being made to produce fluorinated fullerenes C6oF v of lower fluorine content (x < 18) [24],... 

Latouche, R., Texier-Boullet, R, and Hamelin, J., Reactivity of silylated compounds with active methylene under microwave irradiation in heterogeneous dry media. Application to the alkali metal fluoride-mediated silyl-Reformatsky reaction. Bull. Soc. Chim. Fr., 130, 535, 1993. 

Even among classically prepared catalysts, metal fluorides just play a minor role in the field of heterogeneous catalysts, but, nonetheless, there are several important reactions for which metal fluorides are the only choice as catalysts. The main scientific aspects as well as examples of applications are reviewed in Refs [1,2]. 

E. Kemnitz and D. H. Menz, Fhiorinated metal fluorides oxides and metal fluorides as heterogeneous catalysts. Prog. Solid State Chem., 26, 97 (1998). 

Additionally, metal fluorides are extremely sensitive to traces of water. Probably due to a combination of specific surface area and susceptibility to hydrolysis, heterogeneous acid catalysts for use in large-scale fluorination processes are usually based on either chromia or 7-alumina, which become fluorinated in situ. 

Recent progress in the development of synthetic routes to metal fluorides, particularly those of aluminium and magnesium, which have high surface areas, has been described in earlier chapters of this volume. The significant catalytic properties of these high surface area (HS) materials have also been emphasized. Here we examine the surface acidities, both Lewis and Brpnsted, of newly synthesized fluorides based on Al and Mg centres and pose the question What is meant by a strong acid in an heterogeneous context ... 

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