CATALYTIC REACTIONS OF HYDROCARBONS OVER PT-PD ALLOYS .2. DEUTERIUM-EXCHANGE OF METHANE AND ETHANE OVER PT-PD ALLOY-FILMS - SURFACE-COMPOSITION OF PT-PD ALLOY SYSTEM

The exchange of deuterium with methane is proposed as a diagnostic tool to estimate the surface composition of Pt-Pd alloy films. Only stepwise exchange has been found on Pt, Pd, and Pt-Pd alloys. From the kinetic parameters (EA and log A) obtained on thick and thin films the surface composition of thick films is predicted. The occurrence of a well-defined compensation effect suggests that the total activity may be calculated from the contributions from platinum and palladium individual active centers, supporting the idea of using deuterium-methane exchange for solving the problem of surface composition. It seems that although the surface of Pt-Pd alloy is in fact enriched with Pd, this occurs to a lesser extent than is foreseen by the theory of alloy segregation. This conclusion finds support in the analysis of one Pt-Pd alloy by Auger electron spectroscopy. The results of a study of C2H6D2 exchange are also reported. © 1979.