Hexamethylenetetramine-Precipitated α-Ni(OH)2 as Precursors for NiO Nanoparticles: Structural and Morphological Characterization.

Influenced by their morphology, nanocrystalline nickel hydroxide and nickel oxide have important technical applications. A simple novel procedure allows for the preparation of α-Ni(OH)2 from nickel nitrate using hexamethylenetetramine (HMTA) as the precipitating agent. The product obtained is free of water, but contains intercalated nitrate and HMTA. Hydroxide samples prepared in this manner decompose in a single step at 350 degrees C and can be used as precursors for NiO. The hydroxide and oxide samples were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and nitrogen physisorption. Depending on the solvent system used during synthesis, a-Ni(OH)2 has a leaf-like or a flower-like morphology. The nickel oxides obtained from these samples consist of nanocubes (average particle size: 15 nm) and nanorods (length: 30-60 nm), respectively. The oxide samples are mesoporous and the corresponding surface areas are 40 and 35 m2/g.

Oxidative Coupling of 1-Naphthols over Noble and Base Metal Catalysts.

Bismuth-promoted platinum catalysts were tested for the oxidative coupling of 2- and 4-substituted 1-naphthols at different temperatures and ambient pressure. The principal final products are the 3,3'-substituted 1,1'-binaphthalenylidene-4,4'-diones and the 4,4'-substituted 2,2'-binaphthalenylidene-1,1'-diones, respectively. Hydrogen peroxide was used as the oxidant. Only naphthols with electron-donating substituents reacted. The corresponding binaphthalenyl diols can be considered as reaction intermediates. Yields of up to 99 % were obtained from 2-methyl-1-naphthol as the starting material within 20 minutes. Probably for steric reasons, the diol is the final product obtained from 2-ethyl-1-naphthol. For 4-methoxy-1-naphthol the outcome is determined by the reaction temperature. At 25 °C the expected 1,1'-dione is the major product, whereas at 60 °C 1'-hydroxy-4'-methoxy-2,2'-binaphthalenyl-1,4-dione is formed; the loss of one methoxy unit and the preservation of the hydroxy group can be explained by the competitive cleavage of one of the two OMe bonds at higher temperature. Unpromoted platinum and a range of other metallic catalysts, including gold and Raney nickel, were also found to be active. The products obtained are brightly colored solids that could be used as dyes. The method described is truly catalytic and environmentally benign. The potential of the technique justifies further research to expand on the applicability of this novel method.

Nickel-cobalt nanoparticles supported on single-walled carbon nanotubes and their catalytic hydrogenation activity.

Single-walled carbon nanotubes were synthesized from graphite using the arc discharge technique. A nickel/yttrium/graphite mixture was used as the catalyst. After purification by sonication in a Triton X-100 solution, nickel-cobalt metal nanoparticles were deposited on the surface of the single-walled carbon nanotubes. The resulting material and/or the nanotubes themselves were characterized by physisorption, Raman spectroscopy, high-resolution transition electron microscopy and X-ray diffraction. Raman spectroscopy indicates that the nanotubes, prepared by the arc discharge technique, are semi-conducting with a diameter centering at 1.4 nm. The average nickel-cobalt particle size is estimated to be in the region of 8 nm. The catalytic activity of the material was examined for the hydrogenation of unsaturated fatty acid methyl esters obtained from avocado oil. The carbon nanotube supported nickel-cobalt particles effectively hydrogenate polyunsaturated methyl linoleate to monounsaturated methyl oleate. In contrast to a conventional nickel on kieselghur catalyst, further hydrogenation of methyl oleate to undesired methyl stearate was not observed.