XPS analysis of β-AlF3 phases with Al successively substituted by Mg to be used for heterogeneously catalyzed Cl/F exchange reactions

A new method of static charge referencing was applied in a XPS study of beta-AlF3 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 Cl/F exchange reactions. In order to adjust their strengths Mg was introduced into the beta-AlF3 lattice. At low amounts of Mg the resulting samples were found to be highly catalytically active in Cl/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 Au4f(7/2) 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 MgF2 like crystallites are formed in the disturbed beta-AlF3 lattice, which are catalytically inactive as MgF2. (C) 1997 Elsevier Science B.V.