Peter M. Valetsky

Selective dehydrolinalool hydrogenation with poly(ethylene oxide)-block-poly-2-vinylpyridine micelles filled with Pd nanoparticles

Abstract Selective dehydrolinalool (3,7-dimethyloct-6-ene-1-yne-3-ol, DHL) hydrogenation to linalool (3,7-dimethylocta-1,6-diene-3-ol, LN, a fragrant substance) was studied with Pd nanoparticles formed in poly(ethylene oxide)-block-poly-2-vinylpyridine (PEO-b-P2VP) micelles with varying solvent composition (‘isopropanol (i-PrOH):water’ ratio) and the pH of the reaction medium. According to transmission electron microscopy (TEM) and atomic force microscopy (AFM), isopropanol fraction and KOH loading control the micellar characteristics governing catalytic properties. The larger and denser the micelles, the slower the reaction due to internal diffusion limitations within the micelles. Denser micelle cores provide better modification of the Pd nanoparticle surface with pyridine units and higher selectivity. The highest selectivity (99.4%) was obtained at pH of 9.4 and 95xa0vol.% of isopropanol. The highest observed TOF value was found to be 24.4xa0s−1 at pH of 13.0 and 70xa0vol.% of isopropanol. KOH and isopropanol were shown both to affect the micelle characteristics and act as modifiers of the catalyst surface. The hydrogenation kinetics was studied and zero order with respect to dehydrolinalool was found.

Platinum nanoparticles generated in functionality-enhanced reaction media based on polyoctadecylsiloxane with long-chain functional modifiers.

Functionality-enhanced nanostructured matrices generated by intercalating polyoctadecylsiloxane (PODS) with octadecene (ODC) or octadecylamine (ODA) are employed as reaction media in which to grow Pt nanoparticles. Small-angle X-ray scattering (SAXS) signatures confirm that the amphiphilic PODS matrix orders into lamellae with a periodicity (d) of 5.24 nm, which corresponds to the siloxy bilayer and a double layer of alkyl tails. The regular packing of the hydrophobic tails becomes distorted upon introduction of ODC or ODA. Incorporation of K[(C2H4)PtCl3].H2O (a Zeise salt) into the PODS/ODC matrix, followed by reduction of the Pt ions by NaBH4 or H2, results in the localization of Pt compounds and nanoparticles along the siloxy bilayers, which remain dimensionally unchanged. Electron density profiles deduced from PODS/ODA, however, provide evidence for considerable structural reorganization upon metalation with H2PtCl6.6H2O. In this case, the siloxy bilayers broaden due to the presence of PtCl62- ions, and the hydrophobic layers become distorted due to the formation of (PtCl62-)(ODAH+)2 complexes. Subsequent reduction by NaBH4 restores the inherent PODS organization, while H2 reduction partially preserves the distorted matrix, indicating that some Pt nanoparticles form in close proximity to the siloxy bilayer. Transmission electron microscopy reveals that relatively monodisperse Pt nanoparticles measuring approximately 1 nm in diameter are located along the siloxy bilayers, whereas anomalous SAXS further indicates that nanoparticles form aggregates of comparable size to d within the PODS double layers.