It is often difficult to prepare complex core/shell nanostructures and novel materials with enhanced activity, selectivity, and durability using traditional pore volume impregnation catalyst preparation methods. Several solution-phase nanoparticle synthesis methods allow for the preparation of monodisperse metal nanocrystals (NCs), materials with unique catalytic, electronic, and optical properties. However, many colloidal routes to supported catalysts involve capping agents that may be difficult to remove from the catalyst (e.g. PVP, thiols, phosphines). The directed synthesis of NCs using easily removed capping agents could substantially improve opportunities for their use as heterogeneous catalysis precursors. In this study, we develop techniques for preparing Ni and Co NCs by reducing metal acetylacetonates with borane tert-butylamine in the presence of oleylamine, oleic acid, and diphenyl ether. These ligands were selected for their low cost, ease of removal, and likely success in colloidal synthesis. Synthetic conditions (reagent stoichiometry, reducing agent, temperature, time) were varied to control NC size, which was preliminarily evaluated with UV-visible spectroscopy. The Ni and Co NCs were deposited onto a high surface area alumina support via spontaneous adsorption; capping agents were removed under flowing H2/N2 at 350 °C for 2 hours. Capping agent removal was confirmed by FTIR spectroscopy before and after the thermal treatment. Metal dispersions for the activated catalysts were determined with H2 chemisorption. Catalytic activity and selectivity was evaluated with alkene and alkyne hydrogenation reactions. For 1-hexyne hydrogenation, the catalytic activity and selectivity of the NC based catalysts were comparable to catalysts prepared via traditional routes, indicating that the colloidal synthesis is a good method for further investigation of Ni and Co catalysts.

Colloidal synthesis, characterization, & selective alkyne hydrogenation by supported Ni and Co nanocrystals

253rd National Meeting (2017)

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