Surface Composition of the CoPd Alloys Studied by Electron Spectroscopies

Abstract

Palladium-based alloys and bimetallic systems are of importance in heterogeneous catalysis. Recently, attention was devoted to studies of the catalytic properties of the Co-Pd binary system. An important issue to consider is the surface composition of this alloy. The aim of the present work was to determine the surface composition of the polycrystalline CoPd alloys in a wide range of constituent concentrations (Co30Pd70 at.%, Co50Pd50 at.% and Co70Pd30 at.%) at temperatures up to 900°C. Quantitative AES and XPS analyses were used for this purpose. To determine the surface composition, the values of the inelastic mean free path (IMFP) for the studied alloys are necessary. These were derived from the elastic peak intensity. The reported values of the IMFP for Pd are in agreement with the data available in the literature. Reasonable consistency of the IMFP values for CoPd alloys and Co was also observed. The surface compositions of the CoPd alloys at room temperature determined by AES and XPS are in good agreement. It has been found that Pd segregates to surfaces of the Co30Pd70 and Co50Pd50 alloys at temperatures above 300 °C.