Showing papers on "Cobalt sulfide published in 2004"

Alumina-supported cobalt–molybdenum sulfide modified by tin via surface organometallic chemistry: application to the simultaneous hydrodesulfurization of thiophenic compounds and the hydrogenation of olefins

Abstract: Surface organometallic chemistry has been used to deposit tin atoms on an alumina-supported cobalt–molybdenum sulfide. The EXAFS spectra at the Mo and Co K-edges were not changed significantly by tin doping, which means that the initial morphology of sulfide phases was preserved during the synthesis. 119 Sn Mossbauer spectroscopy indicated that the main neighbors of the deposited tin atoms were sulfur and oxygen atoms with no significant formation of metallic tin particles. Tin seems thus to have been deposited either on the sulfide slabs through sulfur bridges or on the support via oxygen bonding. According to the infrared spectroscopy, tin doping led to the blocking of different surface sites with slight electronic structure modification. Those surface sites are sulfur vacancies on sulfide slabs, Al3+ or hydroxyl groups on the support, or “interfacial” sites: support hydroxyl groups H-bonded with sulfide phases. The impact of tin doping on the activity and selectivity of the sulfide phases was studied by catalytic tests carried out using a synthetic FCC gasoline feed. Three main reactions were found to be involved: hydrodesulfurization of sulfur-containing molecules, double-bond isomerization and hydrogenation of olefins. Olefin hydrogenation was preceded by double-bond isomerization reaction, which gave quickly thermodynamically equilibrated composition. No clear correlation could be made between tin doping and isomerization performance and catalyst support was proposed as the main actor for this reaction. Small amounts of tin had little effect on the hydrogenation activity, but higher loadings resulted in an important decrease in activity. Contrary to the case of olefin hydrogenation, thiophene hydrodesulfurization activity decreased drastically at a low tin loading, and continued to decrease but more slightly at higher loadings. By comparison of the activity variations and the characterization results, the sulfur vacancies were found to play a major role in the hydrodesulfurization process. Interfacial sites were assumed to be involved in one of the key steps in the olefin hydrogenation pathway.

Relation between surface preconditioning and metal deposition in direct galvanic metallization of insulating surfaces

Abstract: The relation between surface preconditioning and metal deposition in the direct galvanic metallization of different insulating polymer surfaces by the so-called PLATO technique was studied using electrochemical and surface analytical methods. AFM, XPS and contact angle measurements show that the chromic acid etching of original polymer surfaces leads to an increase of the surface energy and hydrophilicity of polymer substrates due to both surface roughening and the formation of -COOH and/or -COH surface groups. However, decisive for the subsequent surface activation with cobalt sulfide is the increase in surface roughness. The influence of the degree of activation and the electrode potential on the kinetics of Ni metallization was studied by current transient measurements on activated line-shaped structures. The results suggest that the electrochemical reduction of cobalt sulfide to cobalt is a necessary step to induce the process of Ni electrodeposition. Successful Ni metallization could be obtained on ABS (acrylonitrile-butadiene-styrene) and PEEK (poly-ether-ether-ketone) surfaces. The lateral propagation rate, Vx, of the depositing Ni layer depends exponentially on the applied potential and was found to be several orders of magnitude higher than the Ni deposition rate, Vz, in the normal z-direction (Vx/Vz=102–104). It was demonstrated that the approach involving cobalt sulfide pre-activation can also be applied successfully for metallization of oxidized porous silicon surfaces.

Method for recovering nickel and/or cobalt sulfide

Abstract: PROBLEM TO BE SOLVED: To provide a method for recovering sulfide precipitates in which a mole ratio of S/(Ni+Co) is controlled to a value of ≤105 equivalent to that of a sulfide formed by using hydrogen sulfide, preferably a value in the vicinity of 1 which is a stoichiometric composition of NiS and CoS, as a method for recovering nickel and/or cobalt sulfide by adding an alkali sulfide to an acidic aqueous solution containing nickel and/or cobalt and precipitating the nickel and/or cobalt sulfide SOLUTION: In the method for recovering the nickel and/or cobalt sulfide, the inside of a reactor vessel is turned to be under nonoxidizing gas atmosphere and then the alkali sulfide is added to the aqueous solution and the sulfide is formed by precipitation, while maintaining an oxidation-reduction potential (Ag/AgCl electrode standard) at -300 to 100 mV COPYRIGHT: (C)2006,JPO&NCIPI

Self-assembly of novel nanowires by thermolysis of fullerene and transition metal thin films

Abstract: A wide range of nanomaterials has been grown by thermal treatment of patterned condensed-phase precursors. We present a systematic study of the thermolysis of fullerene, amorphous carbon and transition metal thin films, trying to bridge previously reported results in the high temperature regime (>900??C) and reporting novel structures for low temperature (<550??C) processing. The synthesis of crystals of single-walled carbon nanotubes from high temperature annealing of patterned, multilayered fullerene and nickel precursor films, could not be reproduced. A thicker fullerene layer in the presence of nickel was, however, transformed into a web-like carbon network. Low temperature processing of similar precursor patterns on sulfur-containing molybdenum grids resulted in the self-assembly of nickel sulfide nanowires and filled MoS2 nanotubes. Cobalt was found to form cobalt sulfide structures. The strongly oxidizing behaviour of iron resulted in an abundance of needle-like molybdenum oxide crystals. None of the structural formations could be seen for amorphous carbon as a substitutional thin film precursor. Based on the ease of changing precursor materials, this simple, scaleable method addresses many nanomaterials, giving new insight into growth mechanisms as well as offering synthesis control for future applications.

Removal of Sulfur Fume by Reactive Absorption Using Cobalt-Containing Absorbents

Abstract: Cobalt sulfide supported on alumina was found to have a potential use as a device trapping elemental sulfur over the temperature range 300−400 °C. Elemental sulfur in the gas phase can be removed during the deep sulfidation reaction with an accompanying phase change from Co9S8 to CoS2. Constant removal efficiency above 90% was achieved regardless of concentration difference in the inlet sulfur within a tested range of 900−4500 ppm. The sorbent can be easily regenerated by using hydrogen gas at the temperature range of 350−400 °C in a very short time period of less than 1 h. A repeated multicyclic test of absorption and regeneration has shown that the process is reversible and there is no appreciable sintering of particle size.

Oxidation of CoS1.023 grains at 823–983 K

Abstract: According to literature, cobalt sulfide oxidizes at higher temperatures in air to dense or porous cobalt (II) oxide. It is in general agreement with predominance phase diagram, but it also may be concluded from the diagram that cobalt sulfate formation should follow oxidation. This paper presents results of an investigation of oxidation in air of CoS 1.023 grains of 0.63-0.80 mm diameter, in the temperature range 823-983 K. It was found that intense emission of SO 2 -a main gaseous product of the process-proceeds only at the beginning during several minutes. Time of this stage increases with temperature and proportionally increases the degree of sulfide transformation. With electron microscopy, internal composition of oxidized grain was revealed. It was found that the grain in general contains unreacted sulfide core surrounded by a dense layer of CoO without sulfate admixture, then porous layers of Co 3 O 4 with up to 20% of cobalt in sulfate form inside and up to several percent at the grain surface.