Thermal effects on Rhodium nanoparticles supported on carbon

EXAFS measurements have been made in the temperature range 5 300 K on rhodium nano-clusters of average diameters 15.9 and 11.5 angstrom (rms dispersion 7.2 and 4.7 angstrom, respectively) supported on carbon, as well as on a Rh reference foil. The preliminary results of the first shell analysis are presented. The Debye temperature is slightly smaller in n-Rh with respect to bulk and decreases when the cluster size decreases. The results of amplitude analysis (coordination number and static DW) are sensitive to the inclusion of the 4th cumulant. In going from bulk Rh to n-Rh and decreasing the nanocluster size the average coordination number decreases and the static disorder increases. A contraction of the average nearest-neighbour distance is observed at 5 K, -0.004 angstrom and -0.009 angstrom for the larger and smaller clusters, respectively, accompanied by a very slight thermal expansion.