APPLICATION OF DEBYE FUNCTION-ANALYSIS TO PARTICLE-SIZE AND SHAPE DETERMINATION IN IR SIO2 CATALYSTS/

Ir/SiO2 samples containing 5 and 10 wt % of iridium have been studied by X-ray powder diffraction (XRD) and TEM. The particle size distribut ion was determined by X-ray diffraction using Debye function analysis (DFA) and Fourier analysis of the diffraction line profile (FALP). Bot h distributions are rather similar. The average diameters determined b y XRD are 1.7 nm (5 wt %) and 1.9 nm (10 wt %) respectively, i.e., dis persions of 0.53 and 0.50. The linear average diameters determined by TEM are 1.5 nm (5 wt %) and 2.0 nm (10 wt %). Debye function analysis reveals that the best theory/experiment agreement is achieved by assum ing that 70% of the metal crystallites have cuboctahedral morphology a nd that the remaining 30% have an icosahedral structure.