Metal fluorides, heterogeneous catalysts

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. 

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. 

XPS is the most commonly used and most useful surface analysis method in catalyst characterization. It can be used for both qualitative and quantitative analysis for almost all kinds of catalysts used in heterogeneously catalyzed reactions. XPS studies of oxide, sulfide, fluoride, halide, etc., catalysts,. supported metal catalysts, Raney or gauze metal catalysts and zeolite catalysts are all possible. The samples can be studied in any of the precursor, calcined, reduced, activated, deactivated, aged or poisoned states. Real industrial catalysts can be analyzed as well as fundamental model systems. Quantitative analysis is possible either with the help of empirical sensitivity factors or by standard-free methods. In the latter case appropriate theoretical models are u.sed with photoionization cross-section tables, inelastic mean free path (X.) data and individ-... 

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