SURFACE-COMPOSITION OF THE COPD ALLOYS STUDIED BY ELECTRON SPECTROSCOPIES

Palladium-based alloys and bimetallic systems are of importance in het erogeneous catalysis. Recently, attention was devoted to studies of th e catalytic properties of the Co-Pd binary system. An important issue to consider is the surface composition of this alloy. The aim of the p resent work was to determine the surface composition of the polycrysta lline CoPd alloys in a wide range of constituent concentrations (Co30P d70 at.%, Co50Pd50 at.% and Co70Pd30 at.%) at temperatures up to 900 d egrees C. Quantitative AES and XPS analyses were used for this purpose . To determine the surface composition, the values of the inelastic me an free path (IMFP) for the studied alloys are necessary. These were d erived from the elastic peak intensity. The reported values of the IMF P for]Pd are in agreement with the data available in the literature. R easonable consistency of the IMFP values for CoPd alloys and Co was al so observed. The surface compositions of the CoPd alloys at room tempe rature determined by AES and XPS are in good agreement. It has been fo und that Pd segregates to surfaces of the Co30Pd70 and Co50Pd50 alloys at temperatures above 300 degrees C. (C) 1997 by John Wiley & Sons, L td.