ON THE LARGE PD SURFACE SEGREGATION AND REACTIVITY OF PD1FE99 AND PD5FE95 DILUTE ALLOYS

The surface composition of Pd1Fe99 and Pd5Fe95 was determined using low energy ion spectroscopy (LEIS). After stabilization by annealing of the samples at 870 K, the Pd enrichment at the surface was found to be very important, since it reaches values as large as 55 and 65 at% respectively for the Pd1Fe99 and Pd5Fe95 alloys. The performances in catalysis of such alloy surfaces were measured for the 1,3-butadiene hydrogenation reaction (at 300 K and 35 Torr for the hydrogen pressure). The activity ((2.1-9.3) x 10(15) molecules cm-2 s-1) and selectivity into butenes (approximately 1) of such Pd-rich surfaces were found to be of the same order of magnitude as for (111) and (110) Pd single crystal faces.