Oxidation State Of Nickel Research Articles

High-Capacity Sol−Gel Synthesis of LiNixCoyMn1−x−yO2 (0 ≤ x, y ≤ 0.5) Cathode Material for Use in Lithium Rechargeable Batteries

Succinic acid assisted sol−gel synthesized layered LiNixCoyMn1−x−yO2 (0 ≤ x, y ≤ 0.5) materials have been studied as cathode materials for lithium rechargeable batteries. TG/DTA studies were performed on the gel precursor and suggest the formation of a layered phase around 400 °C. The gel precursor was calcined at 850 °C and characterized by means of X-ray diffraction and FT-IR analyses and reveals that all of the synthesized materials are found to be well-crystallized with an α-NaFeO2 layered structure. The effect of Co content on the surface morphology has been examined by scanning electron microscopy, and X-ray photoelectron spectroscopy studies indicate that the oxidation states of nickel, cobalt, and manganese are +2, +3, and +4, respectively. The electrochemical galvanostatic charge/discharge cycling behavior of the synthesized layered materials has been evaluated in the voltage range of 2.7−4.8 V at C/10 and C/5 rates using a 2016 coin-type cell using 1 M LiPF6 in 1:1 EC/DEC as electrolyte. LiCo0.1...

Studies of catalytic activity and coke deactivation of spinel oxides during ethylbenzene dehydrogenation

Catalytic dehydrogenation of ethylbenzene with CO 2 to produce styrene was carried out on MAl 2O 4 (where M = Cu 2+, Ni 2+, or both), and also with pure NiO and CuO catalysts. The synthesized materials were characterized by various physico-chemical techniques and catalytic activity, coke deactivation, and recycling of spent catalysts were studied. The NiAl 2O 4 phase showed the highest activity under moderate conditions (activity = 160 × 10 −3 mol g −1 h −1; selectivity to styrene = 90.7%). Pure NiO and CuO were virtually inactive in the reaction due to the easy reduction of the phases in these oxides. NiAl 2O 4, an active phase for the reaction, was cooperatively associated with Cu in a highly stable ternary system (Cu-Ni-Al). However, this association did not result in high conversion or selectivity. Analyses of the coked catalysts revealed the presence of carbon on the solid surface that was in the form of graphite and polyaromatics. Deactivation studies on NiAl 2O 4 proved that Ni 2+ sites were covered with a moderate amount of crystalline graphite that grew progressively and was subsequently eliminated by using higher CO 2/EB ratios. These results suggest that a reverse water shift reaction may be occurring when this solid is used. On the other hand, polyaromatic carbons were not eliminated and were the leading cause of the catalyst deactivation, rather than the physical degradation (reduction) of the solid. Recycling studies have demonstrated the high tendency of NiAl 2O 4 to regain the oxidation state of nickel, and thus, the styrene selectivity was maintained for over 40 h. The conditions leading to the highest conversion were a CO 2/EB ratio of 30 and a T = 550 °C at ambient pressure. Under these conditions, activities were comparable to those of Fe-K commercial catalysts for dehydrogenation, leading over the steam.

Structure and Mechanism of Copper- and Nickel-Substituted Analogues of Metallo-β-lactamase L1

In an effort to further probe metal binding to metallo-beta-lactamase L1 (mbetal L1), Cu- (Cu-L1) and Ni-substituted (Ni-L1) L1 were prepared and characterized by kinetic and spectroscopic studies. Cu-L1 bound 1.7 equiv of Cu and small amounts of Zn(II) and Fe. The EPR spectrum of Cu-L1 exhibited two overlapping, axial signals, indicative of type 2 sites with distinct affinities for Cu(II). Both signals indicated multiple nitrogen ligands. Despite the expected proximity of the Cu(II) ions, however, only indirect evidence was found for spin-spin coupling. Cu-L1 exhibited higher k(cat) (96 s(-1)) and K(m) (224 microM) values, as compared to the values of dinuclear Zn(II)-containing L1, when nitrocefin was used as substrate. The Ni-L1 bound 1 equiv of Ni and 0.3 equiv of Zn(II). Ni-L1 was EPR-silent, suggesting that the oxidation state of nickel was +2; this suggestion was confirmed by (1)H NMR spectra, which showed relatively sharp proton resonances. Stopped-flow kinetic studies showed that ZnNi-L1 stabilized significant amounts of the nitrocefin-derived intermediate and that the decay of intermediate is rate-limiting. (1)H NMR spectra demonstrate that Ni(II) binds in the Zn(2) site and that the ring-opened product coordinates Ni(II). Both Cu-L1 and ZnNi-L1 hydrolyze cephalosporins and carbapenems, but not penicillins, suggesting that the Zn(2) site modulates substrate preference in mbetal L1. These studies demonstrate that the Zn(2) site in L1 is very flexible and can accommodate a number of different transition metal ions; this flexibility could possibly offer an organism that produces L1 an evolutionary advantage when challenged with beta-lactam-containing antibiotics.

Mixed conductivity, Mössbauer spectra and thermal expansion of (La,Sr)(Fe,Ni)O3−δ perovskites

Abstract The incorporation of Sr2+ in perovskite-type La1 − ySryFe1 − xNixO3 − δ increases oxygen deficiency and ionic transport at elevated temperatures, but leads to a lower thermodynamic stability as reflected by narrowing the solid-solution domain at 1373 K down to x ≈ 0.25 at y = 0.10 and x ≈ 0.12 at y = 0.20 in air. The average thermal expansion coefficients of La1 − ySryFe1 − xNixO3 − δ (x = 0.1–0.4, y = 0.1–0.2) ceramics vary in the ranges (12.4–13.4) × 10− 6 K− 1 at 700–1150 K and (14.2–18.0) × 10− 6 K− 1 at 1150–1370 K, rising with strontium and nickel contents. These additives lower also the temperature of orthorhombic → rhombohedral phase transition visible in the dilatometric curves, promote hole delocalization, increase total conductivity and decrease Seebeck coefficient studied in the oxygen partial pressure range from 10− 5 to 0.4 atm at 973–1223 K. The steady-state oxygen permeation fluxes through single-phase La1 − ySryFe1 − xNixO3 − δ (x = 0.1–0.2, y = 0.1–0.2) membranes, with an activation energy of 206–235 kJ/mol, are determined by both surface-exchange and bulk ionic conduction limited by the oxygen-vacancy concentration. Doping with nickel has a weak negative effect on the oxygen transport, probably due to defect cluster formation involving the vacancies and Ni2+. On the contrary, at low temperatures when (La,Sr)(Fe,Ni)O3 − δ becomes almost oxygen-stoichiometric in air, the Mossbauer spectroscopy and thermogravimetric analysis showed that the average oxidation state of nickel is higher than + 3, similar to iron cations.

High-temperature oxygen non-stoichiometry, conductivity and structure in strontium-rich nickelates La 2− xSr xNiO 4− δ ( x = 1 and 1.4)

Oxygen non-stoichiometry, electrical conductivity and thermal expansion of La 2− x Sr x NiO 4− δ phases with high levels of strontium-substitution (1 ≤ x ≤ 1.4) have been investigated in air and oxygen atmosphere in the temperature range 20–1050 °C. These phases retain the K 2NiF 4-type structure of La 2NiO 4 (tetragonal, space group I4/ mmm). The oxygen vacancy fraction was determined independently from thermogravimetric and neutron diffraction experiments, and is found to increase considerably on heating. The electrical resistivity, thermal expansion and cell parameters with temperature show peculiar variations with temperature, and differ notably from La 2NiO 4± δ in this respect. These variations are tentatively correlated with the evolution of nickel oxidation state, which crosses from a Ni 3+/Ni 4+ to a Ni 2+/Ni 3+ equilibrium on heating.

An unusual base-controlled equilibrium between monomeric and dimeric nickel(IV)–dimethylglyoxime complexes

Ionic nickel(IV)–dimethylglyoxime complexes have been prepared by oxidation of nickel(II)–dimethylglyoxime in alkaline solutions with ferricyanide. A novel base-controlled equilibrium is demonstrated between the monomeric and dimeric nickel(IV)–dimethylglyoxime complexes in solution. The oxidation state of nickel as +4 is confirmed by titration with hydroxylamine salt. The results obtained from the UV/VIS spectrophotometry, titrimetry, infrared and NMR studies are discussed.

Metal Oxide Catalysts for the Evolution of O2 from H2O

This paper describes an iron-nickel oxide catalyst that can eliminate oxygen overvoltage in the electrolysis of alkaline water. Oxygen overvoltage is the largest source of energy loss in water electrolysis. A method for cathodic electrodeposition of first-row transition metal oxides for use as catalysts is described, and the effects of the electrodeposition variables on catalytic performance and catalyst composition were explored. The NiFe oxide catalyst achieved a nearly ideal anodic electron-transfer coefficient, αa = 0.0082 (14.8 mV/decade) in a 1 M KOH solution. The metal oxide catalysts reported here could produce hydrogen and oxygen from water at approximately the thermodynamic potential for small currents. Both transmission electron microscopy and X-ray photoelectron spectroscopy experiments indicated that the NiFe oxide was composed of small crystals (∼1 nm) connected with an amorphous phase and contained a highly disordered arrangement of all nonmetallic nickel and iron oxidation states. Changes ...

Microwave-enhanced catalytic degradation of 4-chlorophenol over nickel oxides under low temperature

Microwave-enhance catalytic degradation (MECD) of 4-chlorophenol (4-CP) using nickel oxide was studied. A mix-valenced nickel oxide was obtained from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite (assigned as PO). Then, the as-prepared PO was irradiated under microwave irradiation to fabricate a high active mix-valenced nickel oxide (assigned as POM). Further, pure nanosized nickel oxide was obtained from the POM by calcination at 300, 400 and 500 °C (labeled as C300, C400 and C500, respectively). They were characterized by X-ray (XRD), infrared spectroscopy (IR) and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of 4-CP on the efficiency of the degradation were further investigated under continuous bubbling of air through the liquid-phase and quantitative evaluation by high pressure liquid chromatography (HPLC). Also, the effects of temperature, pH and kinds of catalysts on the efficiency of the degradation have been investigated. The results showed that the 4-CP was degraded completely by MECD method within 20 min under pH 7, T = 40 °C and C = 200 g dm −3 over POM catalyst. The relative activity was affected significantly with the oxidation state of nickel.

Combined Temperature-Programmed Processes, Pulse Reactions, and On-Line Mass Spectroscopy Study of CH4, CO, and H2Interaction with Ni/Al2O3Catalysts

The interactions of CH4, CO, and CH4/O2 with Ni/Al2O3 catalysts were examined by the pulse reaction technique and the transient response technique. The adsorption and dissociation of CH4, CO, CH4/CO2, and CH4/O2 on nickel alumina catalysts were also extensively investigated by temperature-programmed hydrogenation (TPH) and temperature-programmed desorption (TPD). The phase structure and nickel oxidation states of Ni/Al2O3 samples were examined by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. XRD, TPR, and XPS results demonstrated that nickel is mainly present as NiO and NiAl2O4 in the as-prepared catalyst, while around 83%−90% nickel is Ni0 after the catalyst is reduced at 700 °C. Methane pulse reactions and transient response analysis demonstrate that the methane oxidation mechanism changes as the nickel oxidation state changes over Ni/Al2O3 when there is no gaseous oxygen present. CH4 is efficiently oxidized into CO and H2 via a direct oxidation mechanism when Ni/...

Dioxygen Activation at Monovalent Nickel

The monovalent oxidation state of nickel has received a growing amount of attention in recent years, in part due to its suggested catalytic role in a number of metalloprotein-mediated transformations. In coordination chemistry, nickel(I) is suitable for reductive activation of dioxygen, provided ligands are used that stabilize this less common oxidation state against disproportionation reactions. Two distinct molecular systems have been explored, which have provided access to new nickel-dioxygen structure types, namely, monomeric side-on and end-on superoxo and trans-micro-1,2-peroxo-dinickel complexes. The geometric and electronic structures of the complexes have been established by advanced spectroscopic methods, including resonance Raman and X-ray absorption spectroscopies, and augmented by density functional theory analyses.

Evaluation of microwave-enhanced catalytic degradation of 4-chlorophenol over nickel oxides

Microwave-enhance catalytic degradation (MECD) of 4-chlorophenol (4-CP) using nickel oxide had been studied. A nickel hydroxide, Ni(OH) 2, was prepared by microwave-assisted heating technique from nickel nitrate aqueous solution and sodium hydroxide (assigned as PM). Then, the as-prepared PM was oxidized by liquid oxidation with sodium hypochlorite (assigned as PMO). Further, pure nanosized nickel oxide was obtained from the PMO by calcination at 300, 400 and 500 °C (labeled as C300, C400 and C500, respectively). They were characterized by X-ray (XRD), infrared spectroscopy (IR) and temperature programmed reduction (TPR). Their catalytic activities towards the degradation of 4-CP on the efficiency of the degradation were further investigated under continuous bubbling of air through the liquid phase and quantitative evaluated by high pressure liquid chromatography (HPLC). Also, the effects of initial concentration, pH, temperature and kinds of catalysts on the efficiency of the degradation have been investigated. The relative activity affected significantly with the oxidation state of nickel and decreased slightly with the particle size of nickel oxide, i.e., PMO (> +2) ≫ C300 (+2, d = 4.1 nm) > C400 (+2, d = 9.4 nm) > C500 (+2, d = 12.0 nm).

Activation of Polymerization Catalysts: Synthesis and Characterization of Novel Dinuclear Nickel(I) Diimine Complexes

The reaction of 1,4-bis(diisopropylphenyl)-aza-1,4-butadienenickel dibromide (1a) with stoichiometric amounts of phenyl Grignard or trimethylaluminum affords the purple Ni(I) complexes 1b and 1c, respectively. Single-crystal X-ray diffraction reveals dinuclear species in the solid state for both compounds. UV/vis spectroscopy supports this rare oxidation state of nickel.

Spectroscopic and Kinetic Studies of the Reaction of Bromopropanesulfonate with Methyl-coenzyme M Reductase

Methyl-coenzyme M reductase (MCR) catalyzes the final step of methanogenesis in which coenzyme B and methyl-coenzyme M are converted to methane and the heterodisulfide, CoMS-SCoB. MCR also appears to initiate anaerobic methane oxidation (reverse methanogenesis). At the active site of MCR is coenzyme F430, a nickel tetrapyrrole. This paper describes the reaction of the active MCR(red1) state with the potent inhibitor, 3-bromopropanesulfonate (BPS; I50 = 50 nM) by UV-visible and EPR spectroscopy and by steady-state and rapid kinetics. BPS was shown to be an alternative substrate of MCR in an ionic reaction that is coenzyme B-independent and leads to debromination of BPS and formation of a distinct state ("MCR(PS)") with an EPR signal that was assigned to a Ni(III)-propylsulfonate species (Hinderberger, D., Piskorski, R. P., Goenrich, M., Thauer, R. K., Schweiger, A., Harmer, J., and Jaun, B. (2006) Angew. Chem. Int. Ed. Engl. 45, 3602-3607). A similar EPR signal was generated by reacting MCR(red1) with several halogenated sulfonate and carboxylate substrates. In rapid chemical quench experiments, the propylsulfonate ligand was identified by NMR spectroscopy and high performance liquid chromatography as propanesulfonic acid after protonolysis of the MCR(PS) complex. Propanesulfonate formation was also observed in steady-state reactions in the presence of Ti(III) citrate. Reaction of the alkylnickel intermediate with thiols regenerates the active MCR(red1) state and eliminates the propylsulfonate group, presumably as the thioether. MCR(PS) is catalytically competent in both the generation of propanesulfonate and reformation of MCR(red1). These results provide evidence for the intermediacy of an alkylnickel species in the final step in anaerobic methane oxidation and in the initial step of methanogenesis.

Physical characterization, electrochemical performance and storage stability of spherical Al-substituted γ-NiOOH

Spherical Al-substituted γ-NiOOH as an individual positive electrode material for a new type of alkaline primary/rechargeable Zn-NiOOH battery was prepared by the chemical oxidation of spherical Al-substituted α-Ni(OH) 2. The spherical Al-substituted γ-NiOOH was characterized by XRD, SEM, FT-IR, TGA-DTG, TPD-MS and HT-XRD. The tap density and average nickel oxidation state were measured. Its electrochemical performance and storage stability were also investigated. The results show that the as-prepared spherical Al-substituted γ-NiOOH has remarkably higher specific discharge capacity and superior storage stability in alkaline electrolyte compared to spherical β-NiOOH.

Role of nickel and vanadium over USY and RE-USY coke formation

Abstract The present paper approaches the role of nickel and vanadium oxidation states in the coke formation from cyclohexane model cracking reaction over USY and RE-USY zeolites. The coke yield increased for both zeolites, USY and RE-USY, due to the presence of nickel and/or vanadium contaminant metals. USY loaded with Ni and V presented about the same reducibility of USY loaded distinctly with Ni or V, when steam deactivation is not applied previously. However, coke formation decreased by a factor of 2 for RE-USY or USY loaded with Ni and V when compared to Ni or V loaded distinctly. This factor was affected neither by oxidation/reduction treatments, nor by rare-earths presence. After oxidation treatment vanadium is the principal responsible for coke formation. For V-USY catalyst the coke yield increase by a factor of 2.7 after reduction, while for Ni-USY catalyst coke yield increase by a factor of 13. For the RE-USY catalyst, the coke formation is strongly inhibited on vanadium sites and promoted on nickel sites. These results suggest that the coke formation on the zeolite acidic sites is influenced by multi-component interaction between Ni-V, Ni-RE and V-RE elements.

Oxygen non-stoichiometry and electrical conductivity of Pr 2− xSr xNiO 4± δ with x = 0–0.5

Oxygen non-stoichiometry and electrical conductivity of the Pr 2− x Sr x NiO 4± δ series with x = 0.0–0.5 were investigated in Ar/O 2 ( pO 2 = 2.5 to 21 000 Pa) within a temperature range of 20–1000 °C. The equilibrium values of oxygen non-stoichiometry and electrical conductivity of these nickelates were determined as functions of temperature and oxygen partial pressure ( pO 2). The nickelates with x = 0–0.5 appear to be p-type semiconductors in the investigated temperature and pO 2 ranges. The nickelates with x = 0.3–0.5 show very feebly marked pO 2 dependencies of the conductivity. Pr 1.7Sr 0.3NiO 4± δ shows the anomalies of the conductivity versus oxygen partial pressure which can be related to the orthorhombic–tetragonal crystal structure transformations. The conductivity of the Pr 2− x Sr x NiO 4± δ samples correlates with the average oxidation state of the nickel cations. The samples with x = 0.5 have the highest nickel oxidation state (≈ 2.5+), the highest [Ni 3+]/[Ni 2+] ratio close to 1 and show the highest conductivity (≈ 120 S/cm) in the whole pO 2 and temperature ranges investigated.

Characterization of Li<sub>1-x</sub>Ni<sub>1+x</sub>O<sub>2</sub> Prepared by Using Tartaric Acid as a Complexing Agent

Li1-xNi1+xO2 powder was prepared by using tartaric acid as a complexing agent. A 1 : 1 : 2 mole ratio of Li : Ni : tartaric acid was used to form carboxylate precursors which were calcined at 650–800 oC for 14–48 h. TGA of the precursors showed that formation of Li1-xNi1+xO2 initiates at 600 oC and above. By using XRD, Li1-xNi1+xO2 with 650–800 oC calcination was detected. Calculated intensity ratios of I(003)/I(104) and I(006+102)/I(101) showed that the best condition is at 750 oC for 34 h. The crystallite size was estimated using the Scherrer equation. AAS and titration techniques showed that Ni3+/(Ni3+ + Ni2+) and mean oxidation state of nickel are 66.50 wt% and 2.67 respectively. EDX showed that the powder was comprised by Ni and O. The faceted particles are shown by SEM. TEM and electron diffraction showed the results that are in accordance with the above.

Structure–activity relationship in the N 2O decomposition over Ni-(Mg)-Al and Ni-(Mg)-Mn mixed oxides prepared from hydrotalcite-like precursors

The decomposition of the nitrous oxide over catalysts prepared by thermal decomposition of Ni-(Mg)-M III (M III = Al or Mn) hydrotalcite-like precursors was studied. The mixed oxides obtained at 500 °C were characterized using various techniques—X-ray diffraction (XRD), BET surface area measurements, temperature-programmed desorption (TPD) and temperature-programmed reduction (TPR). The N 2O decomposition was performed in the temperature range 300–450 °C, at 0.05–0.15 mol% inlet N 2O concentrations; oxygen and nitrogen dioxide were added in some runs. The Ni-Al and Mg-Mn catalysts exhibited high catalytic activity but those containing both transition metal cations (i.e. Ni and Mn) were less active. Their lower activity was interpreted in terms of different oxidation states of manganese and nickel in the mixed oxide systems. Up to a certain value of oxygen pressure the presence of oxygen in the reaction mixture caused an inhibition of the reaction rate, while at higher oxygen pressures the N 2O conversion remained nearly constant. The correlation between the observed oxygen inhibition and the proposed N 2O decomposition mechanism as well as the relationship between the observed activity and the amount of reducible components determined from TPR experiments are discussed.

Partial oxidation of methane to hydrogen and carbon monoxide over a Ni/TiO2 catalyst

Abstract Partial oxidation of methane to hydrogen and carbon monoxide (POM) over a Ni/TiO 2 catalyst has been investigated using a fixed-bed reactor. Ni/TiO 2 catalyst has high initial activity but undergoes deactivation during POM. Activation of methane on Ni/TiO 2 was studied by employing a pulse reaction technique in the absence of gas phase oxygen. Methane pulse reactions demonstrate that the methane oxidation mechanism changes as the nickel oxidation state changes over Ni/TiO 2 . CH 4 is efficiently oxidized into CO and H 2 via a direct oxidation mechanism when Ni/TiO 2 is reduced; while CH 4 may be converted by a non-selective oxidation process over oxidized Ni/TiO 2 .

Synthesis of Li 1−xNi 1+xO 2 using malonic acid as a chelating agent

Li 1− x Ni 1+ x O 2 powder was synthesized by polymerised complex method using malonic acid as a chelating agent. The carboxylate precursor was calcined in the temperature range 650–800 °C for 14–48 h. The TG curves of malonic acid, lithium acetate dihydrate, nickel acetate tetrahydrate and the precursor were studied at 29.52–600 °C. The FTIR spectra of the precursor without and with 650–800 °C calcination were used to explain the vibrational bonding. At 750 °C and above, only Li 1− x Ni 1+ x O 2 phase was detected. The maximum [ I (003)/ I (104)] and minimum [ I (006+102)/ I (101)] intensity ratios of the XRD spectra were used to determine the optimum temperature and time of calcination for preparation of Li 1− x Ni 1+ x O 2 powder. In addition, formation mechanism of Li 1− x Ni 1+ x O 2 is proposed. The content of nickel, lithium, Ni 3+/(Ni 3+ + Ni 2+) and mean oxidation state of nickel at 650–800 °C were determined and they show very good agreement. The SEM micrograph is also used to explain the morphology of the powder.