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

The surface composition of Pd1Fe99 and Pd5Fe95 was determined using lo w 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% res pectively for the Pd1Fe99 and Pd5Fe95 alloys. The performances in cata lysis of such alloy surfaces were measured for the 1,3-butadiene hydro genation reaction (at 300 K and 35 Torr for the hydrogen pressure). Th e activity ((2.1-9.3) x 10(15) molecules cm-2 s-1) and selectivity int o 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 crysta l faces.