Benzene hydrogenation activity of nickel catalysts prepared from amorphous Ni-Zr alloys

The hydrogenation of benzene over amorphous Ni-Zr alloys with different Ni compositions (Ni₃₃Zr₆₇, Ni₄₀Zr₆₀, Ni₅₀Zr₅₀, Ni₇₀Zr₃₀, Ni₉₀Zr₁₀) produced by means of a rapid solidification technique was investigated. Although the catalytic activities of the alloys were very low in the virgin state, they gradually increased with increasing number of regeneration (oxidation and reduction) reaction cycles, and the activity approached a constant value after six regenerations. The benzene hydrogenation activity increased with nickel content up to 50%, but then decreased with Ni content. It was shown that the surface area measured by the nitrogen adsorption method had almost the same dependence on Ni content. These results suggest that the Ni₅₀Zr₅₀ alloy is easily relaxed by the regeneration, and Ni atoms effective for the hydrogenation are highly dispersed on the micro ZrO₂ crystals produced from the alloy by the oxidation.     

Effect of copper additive on Zr0.9Ti0.1V0.2Mn0.6Cr0.05Co0.05Ni1.2 alloy anode for nickel–metal hydride batteries

Zr_1–x Ti _x V_0.2Mn_0.6Cr_0.05Co_0.05Ni_1.2 (0 x 0.3) alloys have been characterized as metal–hydride electrodes for nickel–metal hydride batteries. Although the alloy electrodes with no Ti substitution in place of Zr exhibit a specific capacity value of 375 mA h g^–1, it has been possible to enhance the specific capacity of the electrodes to 395 mA h g^–1 by substituting 10% Ti in place of Zr, that is, with Zr_0.9Ti_0.1V_0.2Mn_0.6Cr_0.05Co_0.05Ni_1.2 alloy. The specific capacity value of Zr_0.9Ti_0.1V_0.2Mn_0.6Cr_0.05Co_0.05Ni_1.2 alloy was further enhanced to 415 mA h g^–1 on copper powder addition. Interestingly, the discharge curves for the latter electrode are quite flat thus providing an advantage of constant specific energy output over the entire regime of electrode discharge. Both a.c. impedance and d.c. linear polarization studies conducted on these electrodes lead to a lower charge-transfer resistance value for the metal-hydride electrode with copper additive suggesting the electrode with copper powder additive to have a higher catalytic activity than those without copper. The electrode with the copper additive also exhibits little change in its capacity over about 100 charge–discharge cycles.     

Electrochemical impedance spectroscopy of oxygen and hydrogen evolution on amorphous alloys in 1 M KOH

The mechanisms of oxygen and hydrogen evolution on amorphous alloys G 14 (Fe₆₀Co₂₀Si₁₀B₁₀) and G 16 (Co₅₀Ni₂₅Si₁₅B₁₀) in 1 M KOH at T = 298 K and 333 K were studied by electrochemical impedance spectroscopy (EIS). Comparative measurements were carried out on polycrystalline Pt electrodes. Impedance spectra in the frequency range 10^?3 Hz ≤ f ≤ 10⁴ Hz were analyzed to determine the kinetic behaviour of amorphous alloys by application of transfer function analysis, using non-linear fit routines. The EIS-data are interpreted in terms of consecutive reaction mechanisms for both oxygen and hydrogen evolution.     

The electrochemical and electrocatalytic behaviour of glassy metals

The suitability of a selection of amorphous alloys as electrocatalysts or as inhibitors for hydrogen evolution (HE) was investigated in 1 m KOH at 25 °C. Mild basic conditions were chosen so as to make direct comparison with other data, where available. The alloys studied were the known glassy alloys Fe₆₇Co₁₈B₁₄Si₁, Co₆₆Fe₄Si₁₆B₁₂Mo₂, Fe₄₀Ni₄₀B₂₀ and Fe₄₀Ni₄₀P₁₄B₆ and an entirely new glassy alloy Zr_73.22Ti_19.71Cu_1.24Fe_5.83. The electrochemical techniques of slow sweep anodic and cathodic polarisation were used, in conjunction with the surface analysis techniques of scanning electron microscopy (SEM) and X-ray analysis, to characterise the alloys and new data has been obtained for all alloys. The glassy alloys were tested in their as-polished state, as well as after surface activation, by ex situ chemical (acid etching) and in situ electrochemical (anodic oxidation in base) pre-treatment. The least corrosion resistant composition, Fe₆₇Co₁₈B₁₄Si₁, displayed the highest activity for HE in the as-polished state and only a minor improvement resulted from surface pre-treatment. Corrosion resistance was partly characterised by the degree to which the passive region increased and the passive region current decreased as a function of pre-treatment. The most corrosion resistant alloy, Zr_73.22Ti_19.71Cu_1.24Fe_5.83, displayed the poorest activity for HE in the as-polished state, but a significant improvement resulted from surface activation by in situ anodic oxidation in basic media. Surface activation by acid pre-treatment reduced the corrosion resistance of the Zr_73.22Ti_19.71 Cu_1.24Fe_5.83 alloy and was, therefore, a non-viable and destructive procedure. However, acid pre-treatment was effective in substantially activating the glassy Co₆₆Fe₄Si₁₆B₁₂Mo₂ and Fe₄₀Ni₄₀P₁₄B₆ alloys towards HE and did not alter the corrosion properties of these compositions. A novel technique for mounting thin alloy specimens has been developed, using an insulating photo-resist coating, resulting in sharply defined electrode edges.     

ZrxCo0.8−xNi0.2−xFe2O4-graphene nanocomposite for enhanced structural,dielectric and visible light photocatalytic applications

Zirconium doped nickel cobalt ferrite (Zr_xCo_0.8−xNi_0.2−xFe₂O₄) nanoparticles and Zr_xCo_0.8−xNi_0.2−xFe₂O₄-graphene nanocomposites were synthesized by a cheap and facile co-precipitation method. Annealing was done at 750 °C for 6.5 h. Spinel cubic structure of prepared nanoparticles was confirmed by X-ray powder diffraction (XRD) technique. Crystalline size of nanoparticles was observed in the range of 18–27 nm. Graphene was synthesized by Hummer's method. Formation of rGO was confirmed by UV-visible spectroscopy (UV-vis) and XRD. Zr_xCo_0.8−xNi_0.2−xFe₂O₄-graphene nanocomposites were prepared by ultra-sonication route. Grain size of nanoparticles and dispersion of nanoparticles between rGO layers was determined by Scanning electron microscopy (SEM). In application studies of nanoparticles and their nanocomposites, photocatalytic efficiency of nanoparticles under visible light irradiation was observed by degradation of methylene blue. Charge transfer resistance was measured by electrochemical impedance spectroscopy (EIS) and the variation in dc electrical resistivity was analyzed by room temperature current voltage characteristics (I-V). Dielectric constant was also evaluated in frequency range from 1 MHz to 3 GHz. All these investigations confirmed the possible utilization of these materials for a variety of applications such as visible light photocatalysis, high frequency devices fabrication etc.     

Microstructures and electrochemical properties of Mg0.9Ti0.1Ni1−xMx (M = Co, Mn; x = 0, 0.1, 0.2) hydrogen storage alloys

Mg-Ni-Ti-based hydrogen storage alloys Mg_0.9Ti_0.1Ni_1−xM_x (M = Co, Mn; x = 0, 0.1, 0.2) were prepared by means of mechanical alloying (MA). The effects of partial substitution of Ni with Co or Mn on the microstructures and electrochemical performance of the alloys were investigated. The result of X-ray diffraction (XRD) shows that the alloys exhibit dominatingly amorphous structures. The electrochemical measurements indicate that the substitution of Ni can dramatically enhance the cycle stability of Mg-Ni-Ti-based alloys. After 50 charge/discharge cycles, the capacity retention rate of the alloy electrodes increases from 30% (Mg_0.9Ti_0.1Ni) to 59% (Mg_0.9Ti_0.1Ni_0.9Co_0.1), 58% (Mg_0.9Ti_0.1Ni_0.9Mn_0.1), 46% (Mg_0.9Ti_0.1Ni_0.8Co_0.2) and 53% (Mg_0.9Ti_0.1Ni_0.8Mn_0.2), respectively. Among these alloys, the Mg_0.9Ti_0.1Ni_0.9Mn_0.1 alloy presents better overall electrochemical performance. The cyclic voltammograms (CV) and anti-corruption test reveal that the electrochemical cycle stability of these alloys is improved by substituting Ni with Co or Mn.     

ESR study of paramagnetic sites in sulfated zirconia

ESR spectroscopy was used to investigate paramagnetic sites in sulfated zirconia. Catalysts derived from zirconium oxide and zirconium hydroxide were studied. It was demonstrated that paramagnetic sites assigned to near-surface F-centers were formed during activation at temperatures above 573 K. The catalyst derived from zirconium hydroxide shows after activation at 873 K two types of paramagnetic sites: F-centers and Zr³⁺ sites. Both F-centers and Zr³⁺ sites in this catalyst form complexes with reagents upon n-butane or hydrogen adsorption at range of 423–523 K in contrast to paramagnetic sites of the oxide-derived catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

High catalytic activity in CO PROX reaction of low cobalt-oxide loading catalysts supported on nano-particulate CeO2–ZrO2 oxides

Co₃O₄/NP-ZrO₂, Co₃O₄/NP-CeO₂ and Co₃O₄/NP-Ce_0.8Zr_0.2O₂ catalysts were prepared via a reverse microemulsion/incipient wetness impregnation (RM–IWI) method. The catalytic properties for CO preferential oxidation (CO PROX) reaction in H₂-rich stream were investigated. The Co₃O₄/NP-Ce_0.8Zr_0.2O₂ catalyst with 1.8 wt.% Co₃O₄ loading has exhibited higher catalytic activity than that of the other two catalysts. The higher catalytic activity might be attributed to the combination effect of the highly dispersed cobalt oxide, the improvement in CeO₂ reducibility due to ZrO₂ incorporation in CeO₂ structures, and the strong cobalt oxide-support interaction.     

Multiple magnetic phase transitions in NixMn1-xCo2O4

We prepared pure-phase Ni_xMn_1-xCo₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles using a low-temperature solid-state reaction method. Magnetization measurement results showed that with Ni doping, the Curie temperature and coercivity of Ni_xMn_1-xCo₂O₄ increased. Multiple magnetic phases that transition from paramagnetic to ferrimagnetic to ferrimagnetic and antiferromagnetic were observed to coexist in the Ni_0.5Mn_0.5Co₂O₄ sample. At low temperatures, the ferromagnetic and antiferromagnetic phases coexist in Ni_xMn_1-xCo₂O₄ (x = 0 and 0.25), and as the concentration of Ni increases, Ni_xMn_1-xCo₂O₄ (x = 0.75 and 1) show a spin glass state. The structure of Ni_xMn_1-xCo₂O₄ (x < 0.5) is mainly affected by cation defects, and by cation substitution when x is greater than 0.5. The results of first-principles calculations show that covalent bonds exist in Ni_xMn_1-xCo₂O₄ and that the strength of the Ni-O bond is greater than that of the Mn-O bond.     

Alcohol Synthesis from Syngas over K2CO3/CoS/MoS2 on Activated Carbon

Supported K₂CO₃/Co–MoS₂ on activated carbon was prepared by a co-impregnation technique and has been characterized by X-ray diffraction (XRD) and BET. Active ingredients ranged from 39 to 66% and included molysulfide and cobalt sulfide. XRD analysis indicates that cobalt and molybdenum sulfides are found in the Co₃S₄ and Co₉S₈ phases. These catalysts were performance tested in a fixed-bed reactor under higher alcohol synthesis conditions, 2000–2400 psig and 270–330°C. Active chemicals on the carbon extrudates decreased the surface area dramatically, as measured by BET. Surprisingly, at the high level of active chemicals, alcohol productivity and selectivity were decreased. An increase in the reaction temperature led to a decrease in the selectivity of methanol and an increase in selectivity of hydrocarbons. Total alcohol productivity was also increased as gas hourly space velocity (GHSV) was increased. Co₉S₈ may play a role in the catalyst aging process. In prolonged reaction periods (140 h), sulfur is lost from the surface, possibly as H₂S. The quantity of Co₉S₈ on the surface appears to increase as the catalyst ages.     

The effect of the change of the structure on oxidative dehydrogenation of propane over cerium–zirconium catalysts

A series of pure CeO₂, ZrO₂, and CeZrO_x mixed metal oxide catalysts were prepared by a wetness impregnation method and were applied to the dehydrogenation of propane to propylene at 500°C and 0.1 MPa. The prepared catalysts were characterized by thermal gravimetric analysis (TGA), Brunauer, Emmett, and Teller (BET), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopes (TEM), Raman spectroscopy, and H₂-TPR. It was observed that the zirconium content of the solid solution of the mixed metal oxide catalyst was 5%–25%, while the zirconium content of the material with phase segregation was higher (50%). The addition of zirconium was proven to decrease the oxygen vacancy concentration on the catalyst surface and change the intensity of (111) crystal of cerium oxide in the catalysts. Among the prepared catalysts, the Ce_0.90Zr_0.10O_x catalyst with the maximum strength of the (111) crystal plane of cerium oxide exhibited the better catalytic oxidation performance for the dehydrogenation of propane to propylene. Compared with ZrO₂ in the blank experiment, the average propane conversion and propylene selectivity of the Ce_0.90Zr_0.10O_x catalyst were increased by 10.78% and 17.95%, respectively.     

Quasicrystalline Structures as Catalyst Precursors for Hydrogenation Reactions

The quasicrystalline structures of alloys with nominal compositions of Al₇₂Ni_13.4Co_14.6 and Al_72.3Ni_7.8Co_19.8 were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. For catalytic application, the solids were leached with an alkaline NaOH solution and tested at 373 K with two model reactions under atmospheric pressure: hydrogenation of crotonaldehyde and acetonitrile. The catalytic activities of these leached alloys were compared to that of a Raney nickel reference catalyst. Catalysts prepared from quasicrystals showed high catalytic activities and high selectivities towards butanal (in crotonaldehyde hydrogenation) and ethylamine (in acetonitrile hydrogenation).     

Effect of AB5 alloy on Ti0.10Zr0.15V0.35Cr0.10Ni0.30 hydrogen storage alloy

The structure and electrochemical characteristics of melted composite Ti_0.10Zr_0.15V_0.35Cr_0.10Ni_0.30 + x% LaNi₄Al_0.4Mn_0.3Co_0.3 (x = 0, 1, 5) hydrogen storage alloys have been investigated systematically. XRD shows that though the main phase of the matrix alloy remains unchanged after LaNi₄Al_0.4Mn_0.3Co_0.3 alloy is added, a new specimen is formed. The amount of the new specimen increases with increasing x. SEM-EDS analysis indicates that the V-based solid solution phase is mainly composed of V, Cr and Ni; C14 Laves phase is mainly composed of Ni, Zr and V; the new specimen containing La is mainly composed of Zr, V and Ni. The electrochemical measurements suggest that the activation performance, the low temperature discharge ability, the high rate discharge ability and the cyclic stability of composite alloy electrodes increase greatly with the growth of x. The HRD is controlled by the charge-transfer reaction of hydrogen and the hydrogen diffusion in the bulk of the alloy under the present experimental conditions.     

Ni catalysts with Mo promoter for methane steam reforming

NiO/Al₂O₃ catalyst precursors were prepared by simultaneous precipitation, in a Ni:Al molar ratio of 3:1, promoted with Mo oxide (0.05, 0.5, 1.0 and 2.0 wt%). The solids were characterized by adsorption of N₂, XRD, TPR, Raman spectroscopy and XPS, then activated by H₂ reduction and tested for the catalytic activity in methane steam reforming.The characterization results showed the presence of NiO and Ni₂AlO₄ in the bulk and Ni₂AlO₄ and/or Ni₂O₃ and at the surface of the samples.In the catalytic tests, high stability was observed with a reaction feed of 4:1 steam/methane. However, at a steam/methane ratio of 2:1, only the catalyst with 0.05% Mo remained stable throughout the 500 min of the test.The addition of Mo to Ni catalysts may have a synergistic effect, probably as a result of electron transfer from the molybdenum to the nickel, increasing the electron density of the catalytic site and hence the catalytic activity.     

Investigation of hydrogen transport through Mm(Ni3.6Co0.7Mn0.4Al0.3)1.12 and Zr0.65Ti0.35Ni1.2V0.4Mn0.4 hydride electrodes by analysis of anodic current transient

Hydrogen transport through such metal-hydride electrodes as Mm(Ni_3.6Co_0.7Mn_0.4Al_0.3)_1.12 and Zr_0.65Ti_0.35Ni_1.2V_0.4Mn_0.4 was investigated in 6 M KOH solution by using potentiostatic current transient technique. From the shape of the anodic current transient and the dependence of the initial current density on the discharging potential, the boundary conditions at the electrode surface were established during hydrogen extraction from the as-annealed and as-surface-treated electrodes. Especially, it was experimentally confirmed that the diffusion-limited boundary condition is no longer valid at the electrode surface during hydrogen transport in case hydrogen diffusion is coupled with either the interfacial charge transfer reaction or the hydrogen transfer reaction between adsorbed state on the electrode surface and absorbed state at the electrode sub-surface. From the transition behaviour of the boundary condition, it was further recognised that the boundary condition at the electrode surface during hydrogen transport is not fixed at the specific electrode/electrolyte system by itself, but it is rather simultaneously determined even at any electrode/electrolyte system by the potential step and the nature of the electrode surface, depending upon e.g. the presence or absence of the surface oxide scales.     

Electrochemical performances of Mm0.7MgxNi2.58Co0.5Mn0.3Al0.12 (x = 0, 0.3) hydrogen storage alloys in the temperature range from 238 to 303 K

A series of experiments have been performed to investigate electrochemical properties of Mm_0.7Mg_xNi_2.58Co_0.5Mn_0.3Al_0.12 (x = 0, 0.3) alloy at various temperatures (238 K, 273 K and 303 K). The results indicate that both alloy electrodes exhibit high dischargeabilities after elemental substitution, above 320 mAh g^?1 even at 238 K. The capacity degradation of the two alloys are primarily ascribed to serious pulverization, other than the oxidation of active components at the initial stage. Moreover, the electrochemical performances of Mm_0.7Mg_xNi_2.58Co_0.5Mn_0.3Al_0.12 (x = 0, 0.3) alloy electrodes depend on the alloy type and testing temperature. Mm_0.7Mg_0.3Ni_2.58Co_0.5Mn_0.3Al_0.12 alloy, consisting of LaNi₅-phase and La₂Ni₇-phase, shows better properties of discharge capacity, cyclic stability, self-discharge and pulverization resistance at the three temperatures than those of single LaNi₅-phase Mm_0.7Ni_2.58Co_0.5Mn_0.3Al_0.12 alloy. The electrochemical kinetics studies indicate that the activation energy of hydrogen diffusion and exchange current density (I₀) of Mm_0.7Mg_0.3Ni_2.58Co_0.5Mn_0.3Al_0.12 alloy are lower than those of Mm_0.7Ni_2.58Co_0.5Mn_0.3Al_0.12 alloy. When the temperature increases from 238 to 303 K, the capacity loss, high-rate dischargeability, exchange current density I₀ and hydrogen diffusion coefficient (D/a²) of the two alloys increases, while capacity retention decreases. Further analysis of kinetics suggests that bulk hydrogen diffusion is the rate-determining step of the battery reaction at low temperature 238 K, and charge-transfer reaction on alloy surface is the rate-determining step when tested at 273 K and 303 K for both alloys. The perfect low temperature discharge capacities of the two alloys can mainly attribute to the decrease of activation energy for hydrogen diffusion after elemental substitution.     

Accumulation of zirconium and nickel by Citrobacter sp

Zirconium in aqueous flows was moderately biomineralized by immobilized Citrobacter N14 cells, in the form of gel‐like deposits, probably comprising a mixture of zirconium hydrogen phosphate (Zr(HPO₄)₂) and hydrated zirconia (ZrO₂). The simultaneous presence of uranyl ion (UO) did not facilitate zirconium deposition and the biomineralization of uranium itself as HUO₂PO₄ was repressed by zirconium in the presence of excess inorganic phosphate, liberated enzymatically. Nickel (Ni²⁺) was not significantly removed from aqueous flows by sorption into cell‐bound zirconium deposits, although cell‐bound hydrogen uranyl phosphate (HUP) facilitated nickel removal via intercalative ion exchange into its polycrystalline lattice. A preformed layer of HUP also promoted zirconium removal, at 100% efficiency at pH 2.6, maintained over 38 column fluid‐volumes before saturation. © 1999 Society of Chemical Industry     

Some Factors Influencing the Morphology of α-Zirconium Phosphate and its Intercalation Reactions with a Bifunctional Thioether Amine

Crystalline samples of -zirconium phosphate, (-ZrP, -Zr(HPO₄)₂·H₂O) have been prepared by decomposition of zirconium fluoride complexes in the presence of phosphoric acid under a variety of conditions. The crystallinity and morphology have been shown to depend on a number of factors including the F^–/Zr⁴⁺ ratio, the concentration of Zr⁴⁺ ions, the material of the reaction vessel and the reaction temperature. Under conditions of rapid precipitation small plate-like crystals of -ZrP are produced whereas under conditions of slow crystallisation larger crystals with a lower aspect ratio are formed. The relative intensities of the d ₀₀₂, d ₁₁₀ and d ₁₁₂ reflections observed by X-ray powder diffraction show a correlation with the crystal morphology as determined by SEM.The intercalation reaction of 4-(methylmercapto)aniline with different samples of -ZrP under a variety of conditions has been studied. Incomplete intercalation is observed in each case, with the extent of intercalation depending on both the morphology of the -ZrP and the reaction conditions. The intercalated amine has been shown to exist as a mixture of protonated cations and neutral molecules.     

Deactivation phenomena during catalytic wet air oxidation (CWAO) of phenol over platinum catalysts supported on ceria and ceria–zirconia mixed oxides

Catalytic wet air oxidation (CWAO) of aqueous solution of phenol was carried out with pure oxygen at 160 °C in a stirred batch reactor on platinum supported oxide catalysts (Pt/CeO₂^c calcined at 650 and 800 °C and Pt/Ce_xZr_1 − xO₂ with x = 0.90, 0.75 and 0.50). The catalysts were characterized before (BET, FT-IR spectroscopy, hydrogen chemisorptions, oxygen storage capacity (OSC)) and after reaction (TPO, elementary analysis, GC–MS and DTA–TGA). The results demonstrate a poisoning of the catalysts during CWAO reaction due to the formation of different forms of carbon deposit on the materials: carbonates and polymeric carbon species. This poisoning phenomenon is limited by the introduction of 50% of zirconium into ceria lattice for the catalysts presenting the lowest surface area. Polymeric deposits play a major role in the catalyst deactivation.     

Optimization of microwave synthesis of Li[Ni0.4Co0.2Mn0.4]O2 as a positive electrode material for lithium batteries

A positive electrode material for lithium ion battery applications was successfully synthesized using microwave irradiation. This microwave synthesis has several merits such as homogeneity of final product and much shorter reaction time compared to conventional synthetic methods. We synthesized spherical [Ni_0.4Co_0.2Mn_0.4](OH)₂ as a precursor by a co-precipitation method. The pelletized mixture of the precursor and lithium hydroxide was calcined under different reaction times and temperatures by applying 1200 W of microwave irradiation at 2.45 GHz. We determined the optimum conditions of microwave synthesis for positive electrode materials. The powders were characterized by X-ray diffraction, scanning electron microscopy, and electrochemical testing. The capacity, its retention, and thermal stability of Li[Ni_0.4Co_0.2Mn_0.4]O₂ synthesized by the microwave synthesis were comparable to the Li[Ni_0.4Co_0.2Mn_0.4]O₂ prepared by the high temperature calcination method.