Search results for "NICKEL"
showing 10 items of 1087 documents
Highly selective generation of vanillin by anodic degradation of lignin: a combined approach of electrochemistry and product isolation by adsorption
2015
The oxidative degradation of lignin into a variety of valuable products has been under investigation since the first half of the last century. Especially, the chance to claim this cheap, abundant and renewable source for the production of the important aroma chemical vanillin (1) was one of the major driving forces of lignin research. So far most of the developed methods fail in technical application since no viable concept for work-up is included. This work represents a combined approach of electrochemical conversion of Kraft lignin and product recovery by adsorption on a strongly basic anion exchange resin. Electrolysis conditions are optimized regarding reaction temperatures below 100 °C…
Determination and evaluation of cadmium, lead and nickel in greenhouse soils of Almerı́a (Spain)
2004
This study determines total levels of three (Cd, Pb and Ni) potentially toxic trace elements in western Almería (Spain) greenhouse surface soil horizons using microwave digestion; it establishes the geochemical baseline concentration, and it investigates possible relationships between soil properties and elemental concentrations. The results show that the soil concentration of these heavy metals is lower than mentioned in the European and Spanish normative, but they are higher than those reported by other authors working on agricultural soils. The obtained geochemical baseline concentrations (mg kg(-1)) were: Cd 0.4-0.8, Pb 2.5-89.9 and Ni 16.1-30.7. Using the upper baseline criterion, 88% …
The nickel-support interaction as determining factor of the selectivity to ethylene in the oxidative dehydrogenation of ethane over nickel oxide/alum…
2021
[EN] Nickel oxides supported on gamma-alumina (Ni-loading from 5 to 30 wt% NiO) have been synthesized and tested in the oxidative dehydrogenation (ODH) of ethane in order to determine the importance of the NiO-support interaction. The best performance was achieved by the catalyst with 15 wt% NiO; higher NiO-loadings lead to the formation of unselective bulk-like NiO and lower Ni-loadings present high proportion of free alumina surface sites. The presence of oxalic acid and/or niobium in the synthesis gel resulted in the formation of NiO particles with similar size, but higher crystallinity and reducibility than the standard 15 wt% NiO catalyst. The obtained results have revealed that, in ad…
Oxidative dehydrogenation of ethane on diluted or promoted nickel oxide catalysts: Influence of the promoter/diluter
2020
Ti- and Nb- containing NiO catalysts have been synthesized by two different preparation methods: i) by precipitation (Me-Ni-O oxides, Me = Nb or Ti), in order to prepare promoted NiO catalysts; and ii) by wet impregnation on TiO or NbO supports, in order to prepare diluted/supported NiO catalysts. The catalysts have been also characterized and tested in the oxidative dehydrogenation of ethane. The catalytic performance of Ti- and Nb-promoted catalysts strongly depends on the composition, although in both cases the optimal one is found at similar Ti or Nb loadings (ca. 90 wt% NiO), showing similar ethylene selectivity in the ODH of ethane (ca. 90% at 10–20% ethane conversion). However, in th…
Nickel oxide supported on porous clay heterostructures as selective catalysts for the oxidative dehydrogenation of ethane
2016
[EN] Porous clay heterostructures (PCH) have shown to be highly efficient supports for nickel oxide in the oxidative dehydrogenation of ethane. Thus NiO supported on silica with a PCH structure shows productivity towards ethylene three times higher than if NiO is supported on a conventional silica. This enhanced productivity is due to the increase in the catalytic activity and especially to the drastic increase in the selectivity to ethylene. Additionally, PCH silica partially modified with titanium in the columns (PCH-Ti) have also been synthesized and used as supports for NiO. An enhanced activity and selectivity to ethylene was found over NiO supported over PCH-Ti compared to the corresp…
2-(N,N-Diethylaminomethyl)-6,7-trihydroquinolinyl-8-ylideneamine-Ni(ii) chlorides: application in ethylene dimerization and trimerization
2020
A series of Ni(II) complexes with the general formula [2-((NEt2)Me)-8-{N(Ar)}C9H8N]NiCl2, where Ar = 2,6-Me2C6H3 in Ni1, 2,6-Et2C6H3 in Ni2, 2,6-i-Pr2C6H3 in Ni3, 2,4,6-Me3C6H2 in Ni4, 2,6-Et2-4-MeC6H2 in Ni5, and 2,4,6-t-Bu3C6H2 in Ni6, has been prepared using a one-pot reaction of 2-(N,N-diethylaminomethyl)-6,7-dihydroquinolin-8(5H)-one with the corresponding aniline and nickel dichloride hexahydrate. The resultant complexes were characterized using elemental analysis and FT-IR spectroscopy, while the mononuclear Ni1 and Ni3 were also the subject of single-crystal X-ray diffraction study. On activation with MMAO, the complexes Ni1–Ni6 displayed good activity in ethylene oligomerization, f…
Ethylene polymerization catalysts based on nickel(II) 1,4-diazadiene complexes: the influence of the 1,4-diazadiene backbone substituents on structur…
1998
Abstract Thermally sensitive dialkyl nickel complexes {DAD(H,H)}Ni(CH2SiMe3)2 and {DAD(Me,Me)}Ni(CH2SiMe3)2 [DAD(X,X)=2,6-iPr2C6H4–NC(X)–C(X)N–C6H4iPr2-2,6] were synthesized and were characterized by X-ray diffraction studies on single crystals. The substituents X on the backbone of the α-diimine ligand significantly influence the conformation of the 2,6-diisopropylphenyl substituents. This effect is thought to be of crucial importance for the polymerization of ethylene when {DAD(X,X)}NiBr2/MAO is used as catalyst. The influence of the catalyst structure, pressure, and temperature on the polymerization activity, molar mass, glass transition temperature, melting temperature and branching o…
Study of nickel corrosion processes by molecular dynamics with reactive potential ReaxFF
2012
Understanding of corrosion processes is important for the study of the durability of materials in aggressive environment. The objective is to provide new lights on the corrosion processes of nickel in aqueous condition with molecular dynamics simulation using a reactive force field "ReaxFF."We are particularly interested by the reaction between water molecules and mono-crystalline surfaces of nickel. No dissociation of water was showed on the surfaces. Moreover, an adsorption of molecules in bilayer was observed, reflecting the mutual polarization between water and nickel, which confirms the charge calculation. The metal surface is positively charged and the first water layer charged negati…
Flow-Injection Solid Phase Partial Least-Squares Spectrophotometric Simultaneous Determination of Iron, Nickel and Zinc
2002
A PLS-2 multivariate calibration method has been developed for the simultaneous determination of iron, nickel and zinc in ternary mixtures by solid phase spectrophotometry associated with flow injection analysis. Fe(II), Ni(II) and Zn(II) form color complexes with 1-(2-thiazolylazo)-2-naphthol (TAN), immobilized on a C18 bonded silica support, at pH 6.4. The proposed procedure is based on the different reaction/retention ratios of the studied ions on the solid support. Bilinear spectrophotometric data of the analytes, fixed in the solid support, were recorded in the 400-800 nm wavelength range as a function of time and a partial least squares (PLS-2) algorithm was used to predict results of…
Continuous-Flow Synthesis of Ni(0) Nanoparticles Using a Cone Channel Nozzle or a Micro Coaxial-Injection Mixer
2015
To synthesize nickel(0) nanoparticles by wet chemical reduction using hydrazine with an average size distribution below 100 nm, two different reactor concepts were developed. With a cone channel nozzle, the reactant solutions were sprayed into a batch for further processing and reduction at elevated temperatures. Another concept uses a micro-coaxial injection mixer connected to a heated tube to establish a fully continuously operating reactor. To shorten the time for reduction of the nickel, salt temperatures up to 180 °C are applied. To avoid uncontrolled residence time, the whole system was pressurized up to 80 bar. Approximately 80 L reactant solution, i.e., 1 kg nickel(0) nanoparticles,…