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.