XPS analysis of fl-A1F 3 phases with A1 successively substituted by Mg to be used for heterogeneously catalyzed C1/F exchange reactions

A new method of static charge referencing was applied in a XPS study of fl-A1F 3 phases with aluminum successively substituted by magnesium. This class of compounds is characterized by strong Lewis acid sites, which are assumed to be the catalytically active sites for C1/F exchange reactions. In order to adjust their strengths Mg was introduced into the fl-A1F 3 lattice. At low amounts of Mg the resulting samples were found to be highly catalytically active in C1/F exchange reactions. 20 nm gold particles were deposited on the sample surface to provide a static charge reference. With the help of this procedure binding energies (BE) of photo peaks as well as kinetic energies (KE) of Auger electron emission peaks are presented in relation to the Au 4f7/2 BE reference. Furthermore, a detailed analysis of the relaxation behavior of the Mg nucleus lead to the conclusion that, at low Mg contents, strong Lewis acidic Mg cations in MgxFy clusters act as the catalytically active sites. At high Mg contents, small MgF 2 like crystallites are formed in the disturbed fl-A1F 3 lattice, which are catalytically inactive as MgF 2. © 1997 Elsevier Science B.V.