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 distribution was determined by X-ray diffraction using Debye function analysis (DFA) and Fourier analysis of the diffraction line profile (FALP). Both distributions are rather similar. The average diameters determined by XRD are 1.7 nm (5 wt %) and 1.9 nm (10 wt %) respectively, i.e., dispersions 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 assuming that 70% of the metal crystallites have cuboctahedral morphology and that the remaining 30% have an icosahedral structure.