X-RAY PHOTOELECTRON AND AUGER-ELECTRON SPECTROSCOPIES AND SURFACE SEGREGATIONS IN PD-RH AND PD-RU MEMBRANE CATALYSTS

Auger electron and x-ray photoelectron spectroscopies are used to esti mate the segregation trends at the surface of Pd-Ru and Pd-Rh alloys. The measurements indicate Pd segregation in the studied systems that a re in agreement with the Miedema criteria based on surface tensions of pure metals. Microscopic model calculations of the surface electronic structure of the relevant alloys show the same trend. Parameters asso ciated with the electronic structure of the alloys are used in order t o explain the experimental data for the hydrogenation reaction on a Pd -Ru alloy membrane catalyst.