EXAFS study of size dependence of atomic structure in palladium nanoparticles

• The scheme of FT and fitting technique for Pd K-EXAFS in nanoparticles was suggested.
• Used technique enabled to go beyond averaged description of nanoparticles structure.
• Structure of core and near-surface regions of Pd nanoparticles was determined.
• Size dependence of atomic structure in Pd nanoparticles was revealed.

Dependence of atomic structure of Palladium nanoparticles on supports Al2O3 and SiO2 upon their size, changed from 1.3 to 10.5 nm, was studied by Pd K-edge EXAFS. To determine the structure of the interior (core) and the near surface regions of nanoparticle, the fitting technique of the Fourier-transforms F(R) of spectra was used, which enabled to overcome instabilities of the obtained structural parameters values. The processing of experimental data was performed using results of the study of features formation in │F(R)│ of Pd K-EXAFS in Pd foil. By this approach it was revealed that the local structure of Pd atoms in the core is similar to fcc structure of bulk Pd, irrespective of size. The percentage of Pd atoms, which can be attributed to the core, upon the particles size was determined and the obtained dependence was described by the “cluster size equation”. In the near surface region of nanoparticles, nearest-neighbors Pd–Pd distances show a large Debye–Waller parameters and the mean bond length slightly contracted for nanoparticles of sizes less than ~2 nm. The effect of small structural distortions in the vicinity of absorbing Pd atom in the near surface region was studied using the cluster model of nanoparticle.