Clusters are agglomerates of a few to some hundred atoms. A large fraction
of the atoms find themselves on a surface site. The geometrical structure o
f a cluster, in contrast to the structure of crystalline bulk material, can
not be described with a repeated, space filling unit cell. Clusters appear
often in regular geometrical polyhedrons, e.g. cuboctahedron or icosahedron
.
The interaction between hydrogen and palladium clusters of different sizes
was investigated. The sorption properties of the clusters are compared with
the well-known properties of Pd bulk material. The Pd clusters reversibly
absorb and desorb hydrogen. The miscibility gap (plateau in the pressure co
ncentration isotherm) narrows with decreasing cluster size and therefore, a
n increased hydrogen solubility was found for Pd clusters as compared to bu
lk Pd. The hysteresis between the absorption and the desorption pressure de
creases with decreasing cluster size. (C) 2000 Elsevier Science B.V. All ri
ghts reserved.