Showing papers on "Nickel published in 2002"

Hydrodechlorination of Trichloroethylene to Hydrocarbons Using Bimetallic Nickel-Iron Nanoparticles

Abstract: High surface-area nickel−iron nanoparticles (1:3 Ni:Fe) have been studied as a reagent for the dehalogenation of trichloroethylene (TCE). Ni−Fe (0.1 g) nanoparticles reduced TCE from a 40-mL saturated aqueous solution (24 ppm) to <6 ppb in 120 min. The dehalogenation reaction, based on the surface area normalized rate constant, was 50−80 times slower using nanoiron or iron filings, respectively. On the bimetallic particles, the reaction occurs by nickel-catalyzed hydrodechlorination. As the iron actively corrodes, the cathodically protected nickel surface chemisorbs hydrogen ions. TCE adsorbed to the Ni surface is thus hydrogenated. This reaction competes kinetically with the evolution of molecular hydrogen. Hydrogenation of the C−Cl bond results in the formation of linear as well as branched saturated and unsaturated hydrocarbons. The final TCE degradation products are predominantly even-numbered saturated hydrocarbons, such as butane, hexane, and octane. The toxic dehalogenation products vinyl chloride ...

Methane reforming over Ni/Ce-ZrO2 catalysts: effect of nickel content

Abstract: The effect of Ni content on the Ni/Ce-ZrO2 catalyst has been investigated in the methane conversion reactions to syngas, such as oxy-reforming, steam reforming and oxy-steam reforming. Among the catalysts examined, Ni/Ce-ZrO2 catalyst with 15% Ni loading exhibits not only the highest catalytic activity and selectivity but also remarkable stability. The TPR results reveal that strong interaction between support and metal exists and that some part of NiO incorporates into the surface of the Ce-ZrO2 support. Combined with H2 chemisorption results, one may deduce that Ni surface area and the chemical environment of nickel, as well as the properties of the Ce-ZrO2 support, play very important roles in the catalytic activity and stability of Ni/Ce-ZrO2 catalysts. It seems that two kinds of active sites, i.e. one for methane and the other for steam or oxygen, are well-balanced on 15% Ni/Ce-ZrO2 catalyst.

Nickel-catalyzed cross-coupling reaction of grignard reagents with alkyl halides and tosylates: remarkable effect of 1,3-butadienes.

Abstract: A new method for the cross-coupling reaction of Grignard reagents with alkyl chlorides, bromides, and tosylates has been developed by the use of a nickel catalyst in the presence of a diene as an additive. This reaction proceeds efficiently at 0−25 °C in THF using primary and secondary alkyl and aryl Grignard reagents. Nickel complexes bearing no phosphine ligands, such as NiCl2, Ni(acac)2, and Ni(COD)2, afford the coupling products in good yields, whereas NiCl2(PPh3)2 and NiCl2(dppp) were less effective. 1,3-Butadiene shows the highest activity as an additive for the present coupling reaction. A plausible reaction pathway was proposed.

Efficient Nickel-Catalyzed [2 + 2 + 2] Cycloaddition of CO2 and Diynes

Abstract: A mild and general route for preparing 2-pyrones from CO2 and diynes is described. Under only 1 atm of CO2, excellent yields of pyrone are obtained using catalytic amounts of Ni(COD)2 and imidazolylidene ligand, IPr. In addition, stoichiometric reactions between the isolated complex Ni(IPr)2, diynes, and CO2 suggest that the pathway involves initial reaction with CO2 as the key step.

Synthesis of nickel nanoparticles in aqueous cationic surfactant solutions

Abstract: The synthesis of nickel nanoparticles by the reduction of nickel chloride with hydrazine in an aqueous solution of cationic surfactants CTAB/TC12AB was studied. It was found that an appropriate amount of NaOH, trace acetone, and an elevated temperature were necessary for the formation of pure nickel nanoparticles. Also, it was not necessary to perform the reaction under a nitrogen atmosphere. X-ray diffraction revealed the resultant particles were pure nickel crystalline with a face-centered cubic (fcc) structure. Their mean diameter was 10–36 nm, increasing with increasing nickel chloride concentration or decreasing hydrazine concentration. When the concentration ratio of hydrazine to nickel chloride was above 40, the mean diameter approached a constant value. The magnetic measurement on a typical sample with a mean diameter of 12 nm showed that the resultant nickel nanoparticles were superparamagnetic due to their extremely small size. The saturation magnetization, remanent magnetization, and coercivity were 32 emu g−1, 5.0 emu g−1, and 40 Oe, respectively. Also, the magnetization was observed to increase with decreasing temperature. All the observed magnetic properties essentially reflected the nanoparticle's nature.

Cleavage of carbon-carbon bonds in aromatic nitriles using nickel(0).

Abstract: The nickel(0) fragment [(dippe)Ni] has been found to react with a variety of aromatic nitriles. Initial π-coordination to the CC and C⋮N bonds of 2-cyanoquinoline is found to lead ultimately to C−CN oxidative addition. 3-Cyanoquinoline reacts similarly, although no η2-CN complex is observed. 2-, 3-, And 4-cyanopyridines react initially to give η2-nitrile complexes that then lead to quantitative formation of C−CN oxidative addition products. Benzonitrile reacts similarly but undergoes reversible insertion into the Ph−CN bond to give an equilibrium mixture of Ni(II) and Ni(0) adducts. A series of para-substituted benzonitriles has been studied in terms of both the position of the equilibrium between (dippe)Ni(η2-arylnitrile) ⇌ (dippe)Ni(CN)(aryl) and the rate of approach to equilibrium, and the Hammett plots indicate a buildup of negative charge at the ipso carbon both in the transition state and the Ni(II) product. Terephthalonitrile gives both η2-nitrile and oxidative addition adducts, as well as dimetala...

Splat shapes in a thermal spray coating process: Simulations and experiments

Abstract: We studied the deposition of nickel particles in a plasma spray on a stainless steel surface using both experiments and numerical simulations. We developed a three-dimensional computational model of free-surface fluid flow that includes heat transfer and solidification and used it to simulate the impact of nickel partcles. In our experiments, particles landing on a polished stainless steel surface at a temperature below 300 °C splashed and formed irregular splats, whereas those deposited on substrates heated above 400 °C formed round disk splats. Simulations showed that formation of fingers around the periphery of a spreading drop is caused by the presence of a solid layer. Droplets that spread completely before the onset of solidification will not splash. To sufficiently delay the instant at which solidification started in our simulations to obtain disk splats, we had to increase the thermal contact resistance between the droplet and the substrate by an order of magnitude. We measured the thickness of the oxide layer on the test surfaces used in our experiments and confirmed that heating them creates an oxide layer on the surface that increases the thermal contact resistance. We demonstrated that the numerical model could be used to simulate the deposition of multiple droplets on a surface to build up a coating.

A general nickel-catalyzed hydroamination of 1,3-dienes by alkylamines: catalyst selection, scope, and mechanism.

Abstract: A simple colorimetric assay of various transition-metal catalysts showed that the combination of DPPF, Ni(COD)(2), and acid is a highly active catalyst system for the hydroamination of dienes by alkylamines to form allylic amines. The scope of the reaction is broad; various primary and secondary alkylamines react with 1,3-dienes in the presence of these catalysts. Detailed mechanistic studies revealed the individual steps involved in the catalytic process. These studies uncovered unexpected thermodynamics for the addition of amines to pi-allyl nickel complexes: instead of the thermodynamics favoring the reaction of a nickel allyl with an amine to form an allylic amine, the thermodynamics favored reaction of a nickel(0) complex with allylic amine in the presence of acid to form a Ni(II) allyl. The realization of these thermodynamics led us to the discovery that nickel and some palladium complexes in the presence or absence of acid catalyze the exchange of the amino groups of allylic amines with free amines. This exchange process was used to reveal the relative thermodynamic stabilities of various allylic amines. In addition, this exchange reaction leads to racemization of allylic amines. Therefore, the relative rate for C-N bond formation and cleavage influences the enantioselectivity of diene hydroaminations.

Effect of nickel, iron and cobalt on growth of aligned carbon nanotubes

Abstract: The effect of pure nickel, iron and cobalt on growth of aligned carbon nanotubes was systematically studied by plasma-enhanced hot-filament chemical vapor deposition. It is found that the catalyst has a strong effect on the nanotube diameter, growth rate, wall thickness, morphology and microstructure. Ni yields the highest growth rate, largest diameter and thickest wall, whereas Co results in the lowest growth rate, smallest diameter and thinnest wall. The carbon nanotubes catalyzed by Ni have the best alignment and the smoothest and cleanest wall surface, whereas those from Co are covered with amorphous carbon and nanoparticles on the outer surface. The carbon nanotubes produced from Ni catalyst also exhibit a reasonably good graphitization. Therefore, Ni is considered as the most suitable catalyst for growth of aligned carbon nanotubes.

Comparative study of inhibition effects of benzotriazole for metals in neutral solutions as observed with surface-enhanced Raman spectroscopy

Abstract: Surface-enhanced Raman spectroscopy has been successfully extended to the study of corrosion inhibition of bare iron and nickel metals. The inhibition effects of benzotriazole (BTAH) for copper, iron, and nickel electrodes in 0.1 M KCl solution were investigated by using both polarization curves and in situ Raman techniques. The protective films formed on copper and iron surfaces, in the presence of BTAH, are characterized as [CuIBTA]n and [FeII(BTA)2]n, respectively. The formation of Fe−N coordinated bonds and the deprotonation of the triazole ring may occur while BTAH interacts with the iron surface. On the contrary, BTAH may interact with the nickel surface as neutral molecules in the whole potential range investigated resulting in a poor inhibition effect. The surface complex is characterized as [Ni−BTAH]. The potential dependence of the Raman spectra on copper and iron shows that the BTA- ion in the surface complex may rebind with H+ at more negative potentials and accordingly the inhibition efficien...

Mesoporous nickel/nickel oxide-a nanoarchitectured electrode

Abstract: Metallic nickel was electrodeposited from aqueous nickel(II) acetate dissolved in the lyotropic liquid crystalline phases of Brij 56 and Brij 78 surfactant templates to form metal films with hexagonal arrays of nanometer-sized channels. The applicability of these materials as inexpensive, large area and low-resistance current collectors was demonstrated by cyclic voltammetry. The redox charge capacity of the surface oxide in aqueous KOH was enhanced by 2 orders of magnitude over that of a nontemplated sample with no detectable impedance of the reaction rate.

Catalysis of the Biginelli Reaction by Ferric and Nickel Chloride Hexahydrates. One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones

Abstract: An efficient synthesis of 3,4-dihydropyrimidinones from the aldehyde, β-keto ester and urea in ethanol, using ferric chloride hexahydrate or nickel chloride hexahydrate as the catalyst, is described. Compared with the classical Biginelli reaction conditions, this new method has the advantage of excellent yields (53-97%) and short reaction time (4-5 hours).

Electronically unsaturated three-coordinate chloride and methyl complexes of iron, cobalt, and nickel.

Abstract: Three-coordinate organometallic complexes are rare, especially with the prototypical methyl ligand. Using a hindered, rigid bidentate ligand (L), it is possible to create 12-electron methyliron(II) and 13-electron methylcobalt(II) complexes. These complexes are thermally stable, and (1)H NMR spectra suggest that the low coordination number is maintained in solution. Attempts to create the 14-electron LNiCH(3) led instead to the three-coordinate nickel(I) complex LNi(THF). Single crystals of LMCH(3) are isomorphous with the new three-coordinate chloride complexes LNiCl and LCoCl. Along with the recently reported LFeCl (Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Chem. Commun. 2001, 1542), these are the only examples of three-coordinate iron(II), cobalt(II), and nickel(II) complexes with terminal chloride ligands, enabling the systematic evaluation of the effect of coordination number and metal identity on M-Cl bond lengths. Electronic structure calculations predict the ground states of the trigonal complexes.

Fabrication of magnetic microfiltration systems using soft lithography

Abstract: Arrays of nickel posts were used as magnetic elements in a microfiltration device that is compatible with microfluidic systems. The combination of microtransfer molding—a soft lithography technique—and electrodeposition generated nickel posts ∼7 μm in height and ∼15 μm in diameter inside a microfluidic channel. Once magnetized by a magnetic field from an external, permanent, neodymium–iron–boron magnet, these nickel posts generated strong magnetic field gradients and efficiently trapped superparamagnetic beads moving past them in a flowing stream of water. These nickel post arrays were also used to separate magnetic beads from nonmagnetic beads.

Electroplating of Ni /W Alloys I. Ammoniacal Citrate Baths

Abstract: The electroplating of Ni/W alloys in ammoniacal citrate baths was studied, in an effort to evaluate the mechanism of the synergetic effect of Ni 2+ ions on the deposition of W, commonly referred to as induced codeposition. The extensive review of the field. published by Brenner in 1963, was summarized and updated. The partial current densities for deposition of Ni and W, as a function of the composition of the solution, the current density, and the rate of mass transport, were determined. There is strong evidence to support the hypothesis that the intermediate, which serves as the precursor for deposition of a Ni/W alloy, is a complex such as [(Ni)(WO)(Cit)(H)] 2 , where Cit is the triply deprotonated anion of citric acid. Analysis of the data indicates that the concentration of this intermediate is in the range of 2-4 mM. Most experiments where done at pH 8.0 and in the presence of a large excess of ammonium hydroxide. The concentration of W in the alloy declines sharply when the pH is increased to a value of 9.0. Alloys rich in W can be deposited in the absence of ammonia. The chemistry of the plating bath, in particular, the relative abundance of the different complexes of nickel and tungstate ions with citrate and NH 3 , as a function of pH and the concentrations of the ligands, is discussed.

Method for fabricating semiconductor device

Abstract: A TFT having stable characteristics is obtained by using a crystal silicon film obtained by crystallizing an amorphous silicon film by using nickel. Phosphorus ions are implanted to regions 111 and 112 by using a mask 109. Then, a heat treatment is performed to getter nickel existing in a region 113 to the regions 111 and 112. Then, the mask 109 is side-etched to obtain a pattern 115. Then, the regions 111 and 112 are removed by utilizing the pattern 115 and to pattern the region 113. Thus, a region 116 from which nickel element has been removed is obtained. The TFT is fabricated by using the region 116 as an active layer.