Powder diffraction of small palladium crystallites

Structure of small palladium clusters has been simulated using Sutton-Chen N-body model potential employing energy relaxation and Molecular Dynamics techniques. Functional relationship is presented describing variation of measured lattice constant of small clusters (D>20 Angstrom) of Pd with their size. The results of the simulations are applied to interpret patterns measured by XRD. The experimental data are presented for samples of 10%Pd on silica catalysts of average particle size of similar to 25 Angstrom and similar to 60 Angstrom.The measurements of lattice constant were done in situ at room temperature in atmospheric pressure of argon and air. The shift of its value with changing atmosphere is attributed to relaxation of outer surface of the clusters during chemisorption of oxygen.