Preparation and characterization of small silica-supported iridium particles from iridium trisacetylacetonate precursor

Iridium particles could be active and selective catalysts for the hydrogenolysis of internal C-C bonds of cyclic molecules, but the preparation and characterization of well-defined iridium metallic particles have not been fully investigated. Iridium particles supported on silica were prepared, beginning with iridium trisacetylacetonate (Ir(AcAc)₃). At room temperature, Ir(AcAc)₃ was physisorbed onto the surface. The decomposition of the precursor under a flow of hydrogen at 300°C produced metallic particles with narrow distributions of sizes 1-5 nm. The dispersions of the metallic particles inferred from electron microscopy observation was always lower than the dispersions computed from the chemisorption of O₂, H₂, and CO, assuming the stoichiometry: CO/Ir_s and O/Ir_s = 1, H/Ir_s = 2. The dispersion estimated from the size of the particle could be underestimated.