Preparation and Characterization of Dendrimer-Derived Bimetallic Ir–Au/Al₂O₃ Catalysts for CO Oxidation

The synthesis of alumina supported Ir–Au bimetallic catalysts using the dendrimer–metal nanocomposite (DMN) approach is reported. The surfaces and nanostructures of four bimetallic DMN-derived samples with similar Ir and Au loading and composition were correlated with their activity for CO oxidation. Results were compared to a catalyst prepared by conventional incipient wetness impregnation of metal salts. Scanning transmission electron microscopy and H₂ chemisorption data reveal that these catalysts have different metallic dispersions with various particle sizes and distributions, depending on the preparation method. Moreover, in situ transmission Fourier transform infrared spectroscopy of CO adsorption allowed for identification of exposed metal surface area in the catalyst. DMN-derived catalysts were tested for CO oxidation, with turnover frequencies calculated in order to determine the intrinsic activity of the samples. Single-pass fixed-bed microreactor measurements show that the activity, measured under identical conditions, differ significantly for these catalysts and are correlated with the catalyst preparation method and with the Au role in the bimetallic catalysts. This points to a distinct Au effect and a direct participation of the Au in the reaction