XPS study of transition metal/alumina model catalysts: Equilibrium and energy referencing

We have used XPS to examine some model catalysts obtained by vapour deposition of Ni, Pd and Pt on an α‐alumina single‐crystal. It is shown that the binding energies of the substrate core levels with respect to the metal Fermi level depend on the metal work function. This is due to the fact that the common reference level between the metal and the insulating support is the vacuum level, although the Fermi level reference only gives a chemical aspect to the binding energy shifts on the metal. The consequences for XPS analysis of supported catalysts or any metal/insulator system are discussed.