Ethanol steam reforming study over ZSM-5 supported cobalt versus nickel catalyst for renewable hydrogen generation

The renewable hydrogen generation through ethanol steam reforming is one of the anticipated areas for sustainable hydrogen generation. To elucidate the role of Ni and Co with ZSM-5 support, catalysts were prepared by wet impregnation method and ethanol steam reforming(ESR) was performed. The catalysts were characterized by HR-XRD, ATR–FTIR, HR-SEM, TEM with SAED, EDAX, surface area analyzer and TPR. It had shown complete ethanol conversion at 773 K, but the selectivity in hydrogen generation was found higher for 10% Ni/ZSM-5 catalyst as compared to 10% Co/ZSM-5. The 10% Ni/ZSM-5 catalyst has about 72% hydrogen selectivity at temperature 873 K. It indicates that Ni is a more sustainable catalyst as compared to Co with ZSM-5 support for ESR. The C_2H_4 was found major undesirable products up to 823 K temperature. Nevertheless, the 10% Ni/ZSM-5 catalyst had shown its stability for high temperature(873 K) ESR performance.     

Reduction of supported cobalt catalysts by hydrogen

The reduction of cobalt catalysts supported on Al₂O₃, SiO₂, and TiO₂ was investigated using a closed system filled with hydrogen gas. Effects of support and metal loading on the rate of reduction were also discussed. The activation energy of reduction increased in the following order: Co/TiO₂2O₃2. For different metal loadings, it was found that the catalyst with the higher loading was more readily reducible than that with the lower metal loading. This was confirmed using the results from measurements of particle size, amount of CO adsorbed and activity.     

Selective separation of cobalt and nickel by supported liquid membranes

The selective separation of cobalt from acidic media, containing both equimolar and nonequimolar mixtures of cobalt and nickel, was examined by supported liquid membranes using Alamine 336 as mobile carrier dissolved in various diluents. The membrane support was microporous hydrophobic polypropylene Celgard 2500 (25 μm thick, 0.209 × 0.054 μm pore size and 55% porosity). Acetic acid-Na acetate buffer was used for the adjustment of the feed pH which was critical. Various parameters were experimentally studied and the optimum conditions were determined.     

Synthesis, electrochemical and electrocatalytic behaviour of thiophene-appended cobalt, manganese and zinc phthalocyanine complexes

This work reports on the syntheses of new thiophene tetra substituted cobalt, manganese and zinc phthalocyanine (CoTETPc, (Cl)MnTETPc and ZnTETPc) complexes. The redox processes due to the thiophene substituent on the ring of the metallophthalocyanines (MPcs) were observed, in addition to Pc ring and metal (for Co and Mn complexes) based redox activity. The electrocatalytic activity of the CoTETPc complex adsorbed on glassy carbon electrode (GCE) by drop/dry-thermal annealing was investigated using l-cysteine. The modified electrode was stable to repetitive use without any signs of deactivation by oxidation products and was used to determine l-cysteine at concentrations between 0.0015 and 1 mM in pH 4 aqueous conditions.     

A cobalt complex of a pentadentate aminopyridine ligand as an efficient catalyst for photocatalytic hydrogen generation

A linear pentadentate aminopyridine ligand 2,6-bis[(methyl(pyrid-2-ylmethyl)amino)-N-methyl]pyridine (Py^Mepam) has been prepared and characterized. This ligand readily coordinates with Co(II) or Zn(II) ions, and the resulting complexes of general formula [M(Py^Mepam)](BF₄)₂ (M = Co (1) and M = Zn (2)) have been thoroughly characterized and investigated for electro- and photocatalytic water reduction in acetonitrile. Electrochemical studies reveal that the complex 1 is active for electrocatalytic water reduction in acetonitrile. Under visible-light irradiation (λ > 400 nm), the complex 1 displays hydrogen evolution activity when in presence of [Ir(ppy)₂(bpy)]PF₆ as photosensitizer and triethylamine (TEA) as electron donor, whereas 2 shows negligible catalytic activity under the same conditions. Highest turnover numbers (TONs) of 290 for H₂ evolution are achieved from an optimized system containing 1 (0.1 mM), [Ir(ppy)₂(bpy)](PF₆) (0.5 mM), and 10 vol% TEA in CH₃CN-H₂O (1/1, v/v) mixed solvents at pH 10.     

Polymer supported synthesis of mixed ligand complexes

A series of novel polymer‐supported mixed ligand complexes were synthesized and studied. Two percent divinyl benzene (DVB)‐crosslinked polystyrene supports were synthesized by the suspension copolymerization technique. An ethylene diamine group was anchored onto the support and the corresponding copper complexes were prepared. The ligating functions like phthalate, acetate, and oxalate groups were introduced, and mixed ligands complexes were synthesized. The resultant polymer supported mixed ligand complexes were characterized by UV‐Vis, IR, and EPR methods. The stability constants dictate the formation of these complexes on polymer support. Spectral results gave information about the structure, stability, and geometry of the mixed ligand complexes. These factors were discussed in detail. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2684–2690, 2003     

Hydrogen adsorption on supported cobalt,iron, and nickel

This paper emphasizes concepts and fundamentals relating to the kinetics, energetics, and stoichiometries of adsorption of hydrogen on supported cobalt, iron and nickel, with emphasis on nickel. Relationships between catalyst and adsorption properties and the application of hydrogen chemisorption to the measurement of metal surface areas are discussed. Evidence is presented for nonstoichiometric adsorption of hydrogen on supported metals and the results are interpreted in terms (i) reversibility of adsorption and (ii) interactions of hydrogen with metal oxides present on or near metal crystallites. Contamination of the metal surface by support moieties can cause (i) the appearance of new adsorption states of hydrogen at higher binding energies and (ii) an increase in the adsorption activation energy for hydrogen which can lead to severe kinetic limitations in the adsorption process. Precalcination treatments and promoters such as potassium also cause the appearance of new high temperature adsorption states and significantly increase the adsorption activation energy for hydrogen.     

Titanium complexes supported by a sterically encumbering N-anchored tris-arylphenoxide ligand

A family of neutral and cationic Ti(IV) complexes supported by the sterically demanding and trianionic ligand (O₃N)³⁻ (O₃N³⁻ = tris(2-O,3-Ad,5-tBubenzyl)amine, Ad = 1-adamantyl) have been prepared from the hydrolysis of TiCl₄(THF)₂ with the free base (O₃N)H₃ and excess NEt₃, followed by anion exchange reactions. These (O₃N)Ti⁺ cores are resistant to moisture and air, are mononuclear, and possess C₃ symmetry on the NMR timescale.     

Synthesis,structures, and magnetic properties of tetranuclear nickel and cobalt complexes with 2-mercaptobenzoxazole

The synthesis and magnetic properties of two tetranuclear Ni complex Ni₄(L)₄(CH₃CN)₄(OCH₃)₄ 1 and Co complex Co₄(L)₄(CH₃CN)₄(OCH₃)₄ 2 (HL = 2-mercaptobenzoxazole) are reported. The X-ray structures reveal that 1 and 2 are isostructural with [Ni₄O₄] 1 and [Co₄O₄] 2 cubane-like cores. Analysis of the temperature dependent magnetic measurements data shows that both complexes are paramagnetic with weak antiferromagnetic coupling. One-J model and two-J model are both applied to fit the experimental magnetic data of 1 and the results indicate the exchange coupling between the type A Ni(II) ions affected by NCS three atoms bridge in 2-mercaptobenzoxazole ligand.     

Mechanistic investigations into electrocatalytic substitution reactions of two diiron hexacarbonyl complexes by triphenyl phosphine ligand

Re-examining electrocatalytic substitution reactions of two diiron hexacarbonyl complexes, [Fe₂(μ-pdt)(CO)₆] (1) (pdt = propane-1,3-dithiolate) and [Fe₂(μ-padmt)(CO)₆] (2) (padmt = (propylazanediyl)dimethanethiolate), reveals that the monoanion of these complexes is the catalytic species rather than their dianion. Detailed mechanisms of electrocatalytic substitution reactions for the two complexes were proposed based on investigations into their electrochemistry without and with the presence of a monodentate ligand PPh₃ by using a variety of cyclic voltammetric techniques and rationalised by digital simulations. Our investigations also demonstrate an alternative methodology for synthesis of substituted diiron carbonyl complexes which have widely been employed as models of the sub-unit of the [FeFe]-hydrogenase. Electrochemical mean requires less organic solvents, no harsh reaction conditions, and no auxiliary agents and thus environmentally more benign than chemical synthesis.     

镍二亚胺配合物/复合载体催化剂合成支化PE

研究了在不用甲基铝氧烷.只以通用烷基铝为助催化剂的条件下,以SiO2和MgCl2的复合载体负载3种镍二亚胺配合物催化乙烯进行聚合,庚烷为溶剂制备支化聚乙烯(PE)。结果发现,聚合条件(如配体、载体改性方式、助催化剂、铝/镍、聚合温度和金属镍浓度等)对催化活性有很大的影响。没有经三乙基铝改性的复合载体负载空间位阻最小的镍二亚胺配合物在以-氯二乙基铝为助催化剂、聚合温度14℃、金属镍浓度0.12 mmol/L、铝/镍为80的条件下催化活性达290 kg/mol·h),生成的支化PE的支化度随着聚合温度的升高而迅速增加,受铝/镍的影响不大     

Synthesis and high performance of ceria supported nickel catalysts for hydrodechlorination reaction

Catalysts containing 10 wt% Ni supported on CeO₂ were prepared by two ways, namely, co-precipitation method using nickel nitrate precursor and impregnation method using nickel nitrate and nickel acetylacetonate as two separate precursors. The catalysts were characterized by pulse chemisorption of H₂, X-ray diffraction, and temperature programmed reduction (TPR) techniques and evaluated for the gas phase hydrodechlorination (HDC) of chlorobenzene to benzene in a fixed-bed down-flow glass reactor at 573 K under normal atmospheric pressure. The hydrogen uptake values were used to determine the catalyst properties of Ni/CeO₂ like dispersion, metal area, and particle size. Among the two preparatory routes, co-precipitation method gave better catalytic performance in terms of hydrogenation activity, benzene selectivity, and coking resistivity than impregnated Ni/CeO₂ catalysts. This may be attributed to high dispersion of smaller NiO crystallites and the appearance of the second reduction peak at a higher temperature (578 K) in TPR profile with co-precipitated Ni/CeO₂ catalyst. This indicates that a strong interaction may take place between the NiO crystallites and CeO₂ on the surface of co-precipitated Ni/CeO₂ catalyst. Contrary to general expectation that the large Ni particles are preferable for HDC reaction, it is observed that smaller metal particles with high dispersion, as in the case of co-precipitated Ni/CeO₂ catalyst, promotes better catalyst with longer life.     

Synthesis and electrocatalytic property of cubic and spherical nanoparticles of cobalt platinum alloys

This paper describes the morphological control and electrocatalytic property of CoPt nanoparticles. Both cubic and spherical CoPt nanoparticles were made using cobalt carbonyl and platinum 2,4-pentanedionate under different reaction temperatures in the presence of capping reagents, which included adamantanecarboxylic acid and hexadecylamine. Effects of heterogeneous species on shape of the CoPt nanoparticles were examined by replacing cobalt carbonyl with silver acetylacetonate. Our results suggest that the formation of different shapes of CoPt particles could be attributed to the affinity between cobalt and platinum, and the effects of capping agents. The size and shape dependent electrocatalytic properties of these nanoparticles were examined based on the direct methanol oxidation reaction.     

Selective separation of cobalt and nickel by flat sheet supported liquid membrane using Alamine 300 as carrier

Cobalt and nickel are among the most important nonferrous metals. The using of flat sheet supported liquid membranes (FSSLMs) to remove metals from wastewaters has been used actively by the scientific and industrial communities. In this study, the selective separation of cobalt from thiocyanate solutions containing cobalt and nickel by FSSLM was examined using tri-n-octylamine (Alamine 300) as carrier. The FSSLM was consisted of extractant, flat sheet support and organic solvent. The various parameters were studied to determine the optimum extraction and striping conditions of cobalt and nickel. These parameters were stirring speeds of phases, NH₄SCN concentration, pH, diluent type, extractant concentration, stripping reagent concentration and modifier concentration. Concentration of cobalt and nickel were determined by Shimadzu AA-6701GF spectrophotometer. In the optimum conditions, selective separation of cobalt was achieved with an efficiency of 98.4% within 8 h, for equimolar feed mixtures, 400 mg/L Co + 400 mg/L Ni, and the separation factor of Co(II) over Ni(II) was 234.4. In addition, for nonequimolar feed mixtures, 500 mg/L Co + 1000 mg/L Ni, Ni in excess, selective separation of cobalt was 99.9%, and the separation factor of Co was 506 in the same time.     

Porous nickel disulfide/reduced graphene oxide nanohybrids with improved electrocatalytic performance for hydrogen evolution

Single porous nickel disulfide (NiS₂) nanoballs and nanohybrids of NiS₂ with reduced graphene oxide (NiS₂/rGO) were successfully prepared by a simple hydrothermal process in the absence or presence of graphene oxide. NiS₂/rGO nanocomposites exhibit remarkable electrocatalytic performance for hydrogen evolution from water splitting due to the plentiful active sites in the porous NiS₂, the improved conductivity and the positive synergetic effect between NiS₂ and rGO. The nanocomposites displayed superior activity for the hydrogen evolution reaction (10 mA cm^− 2 vs. − 200 mV, Tafel slope of 52 mV dec^− 1) and an excellent electrocatalytic stability.     

Stability of metal nanoparticles formed during reduction of alumina supported nickel and cobalt catalysts

The formation of nickel and cobalt nanoparticles in hydrogenation catalysts and their stability against sintering during the reduction of the oxidic precursors were investigated. The morphology of the catalysts was manipulated by varying the reduction conditions. The catalysts were characterized using temperature programmed reduction (TPR), hydrogen chemisorption, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HREM). The transformation of the oxidic precursor into the active phase was monitored using quasi in situ HREM, which proved to be an excellent technique to visualize the formation of metal nanoparticles. For the nickel catalyst the reduction temperature plays a crucial role, whereas time is more critical for the cobalt catalyst. The sintering rate of cobalt is considerably lower than that of nickel during reduction. It is concluded that the activation energy for sintering is significantly higher for nickel than for cobalt. A model is proposed which depicts the structure of both types of catalysts in their oxidic and reduced state. TPR and XPS results indicate that the passivated catalysts contain approximately two oxygen atoms per surface Ni or Co atom.     

A kinetic study on the electrodeposition of nickel nanostructure and its electrocatalytic activity for hydrogen evolution reaction

The electrodeposition of nickel was studied using electrochemical techniques in different electrolytes and various agents. The voltammetry analysis clearly showed that the electrodeposition of nickel was a diffusion-controlled process associated with a typical nucleation process. The current transients represented instantaneous nucleation with a typical three-dimensional (3D) growth mechanism. Scharifker’s equations were derived for instantaneous and progressive nucleation of the 3D growth of the spherical centers under diffusion-controlled condition. The number of nucleation sites increased with the increment in overpotential and Ni²⁺ concentration. Atomic force microscopy was used to confirm the presumed model. Also, the electrocatalytic activities of the Ni films were investigated for hydrogen evolution reaction (HER). The electrocatalytic activity of the Ni nanostructure was three times higher than the 2D Ni microstructure when the overpotential of −1.2 V was applied. The HER current density at −1.4 V for Ni nanostructure (−20 mA cm⁻²) was considerable with respect to the Ni microstructure (−8.46 mA cm⁻²) too.     

Pyrolysed carbon supported cobalt porphyrin: a potent catalyst for oxidation of hydrogen sulfide

Pyrolysed carbon supported cobalt porphyrin, an electrocatalyst that is frequently used for oxygen reduction in fuel cells, is evaluated for catalytic oxidation of hydrogen sulfide by dissolved dioxygen. The catalyst performs best after heat treatment at 880 °C_, at pH 8. Analysis of the reaction products reveals that sulfur is the dominant product throughout the investigated pH range 5–10. The catalyst performs much better than powdered activated carbon, granular activated carbon and different other forms of unmodified carbon catalysts. This is as far as we know the first time that heat treated cobalt porphyrins are evaluated for non-electrocatalytic applications.     

Mechanistic study of cobalt,nickel and copper transfer across a supported liquid membrane

The mechanism of cobalt, copper and nickel transport through supported liquid membranes containing di(2-ethylhexyl)phosphoric acid as a mobile carrier has been studied. An equation describing the permeation rate has been derived, taking into account stagnant layer aqueous diffusion, interfacial resistance due to solvatation reaction and liquid membrane diffusion as simultaneous controlling factors. The validity of this model is evaluated with experimental data of mass transfer coefficient measured employing a permeation cell. For these ions it was found that at low stirring conditions the stagnant layer resistance mainly controlled the processes, but it is controlled by diffusion of the ion complex through the supported liquid membrane when the stagnant layer resistance is negligible.