The synthesis of Ir/γ-Al₂O₃ using the dendrimer metal nanocomposites (DMN) approach is reported. The dendrimer is used as a templating agent to control the final Ir particles sizes. The maximum complexation of Ir-dendrimer results in a substitution of two chloride ions from the precursor with two oxygen ions from the dendrimer functional groups. In-situ transmission Fourier transform infrared spectroscopy during dendrimer thermal decomposition in different environments and CO adsorption provides identification of catalyst activation treatments that expose the maximum metal surface area. The particle size distributions of these catalysts were investigated, revealing that all alumina supported catalysts have small particle sizes with narrow distributions, whereas silica supported catalysts show larger particle sizes. An optimized oxidation/reduction treatment resulted in notable differences between DMN-derived and conventional samples. Bimetallic Ir-Pd/γ-Al₂O₃ prepared using the DMN approach and conventional wet impregnations were used for hydrogenation of benzonitrile in liquid phase, where these catalysts show remarkable differences in activity and selectivity.