Pd-Pt nanoclusters are obtained by the focusing of an Nd:YAG laser onto rod
s of alloys. The aggregates, which are produced by plasma cooling via short
helium bursts synchronized with the laser pulses, are collected on amorpho
us carbon or silicon substrates, in a UHV chamber. Transmission electron mi
croscopy (TEM) experiments show that the diameters of the clusters range be
tween 1.5 and 4.5 nm, and analytical microscopy indicates that they have th
e same composition as the vaporized rods. Low-energy ion scattering (LEIS)
also shows that the surface of the obtained clusters is Pd enriched: the Pd
concentration in the first atomic layer is found to be equal to 38% for a
Pd17Pt83 rod composition and 87% for the Pd-65 Pt-35 ahoy. The catalytic ac
tivity of these clusters in the hydrogenation of 1,3-butadiene to butenes a
nd butane is measured in static mode, with mass spectrometry detection. The
reactivity of the bimetallic clusters is explained by the atomic local ord
er and low-coordination sites considered as "hot sites".