Oxide nickel species

The basic electrochemistry of the Ni-Cd battery was given in Table IIJ once again, however, the equations are misleading in that the reactions are not nearly as simple as indicated particularly at the positive electrode. In the nickel oxide paste, the oxidation state of the oxidized nickel species is uncertain and varies between - 2 and h-4 both the oxidized and reduced species exist in several crystal modifications and the important roles of water and potassium ions arc not included in the table. 

Ordinarily, this principle is applied at standard concentrations (1 atm for gases, 1M for species in aqueous solution). Hence it is the sign of E° that serves as the criterion for spontaneity. To show how this works, consider the problem of oxidizing nickel metal to Ni2+ ions. This cannot be accomplished by using 1M Zn2+ ions ... 

Fig. 1 compares the activities of vanadium-, cobalt- and nickel- based catalysts in ODH of ethane. Representative catalysts contained between 2.9 and 3.9 wt.% of metal. It is to be pointed out that metal oxide-like species was not present at any of the catalysts, as its presentation is generally the reason in the activity-selectivity decrease. The absence of metal oxide-like species was evidenced by the absence of its characteristic bands in the UV-Vis spectra of hydrated and dehydrated catalysts (not shown in the Figure). The activity of catalysts was compared (i) at 600 °C, (ii) using reaction mixture of 9.0 vol. % ethane and 2.5 vol. % oxygen in helium, and (iii) contact time W/F 0.12 g. i.s.ml 1. These reaction conditions represent the most effective reaction conditions for V-HMS catalysts [4] The ethane conversions, the ethene yields and the selectivity to ethene varied between 13-30 %, 5-16 %, and 37-78 %, respectively, depending on the type of metal species (Co, Ni, V) and support material (A1203, HMS, MFI). 

The form of nickel emitted to the atmosphere varies according to the type of source. Species associated with combustion, incineration, and metals smelting and refining are often complex nickel oxides, nickel sulfate, metallic nickel, and in more specialized industries, nickel silicate, nickel subsulfide, and nickel chloride (EPA 1985a). 

The active catalyst is presumably formed through reduction of the Ni species, aided by hydrogen or group VIB metals and their carbonyls, to the nickel carbonyl. Nickel carbonyl is converted to the active catalyst by ligand dissociation. The exact nickel species is the result of complex equilibria, equations 11-17. The zero valent complex adds methyl iodide, after CO dissociation. This is believed to be the rate-determining step and has first order kinetics with respect to both iodide and Ni. It was found that temperature greater than 100 C is needed for the oxidative addition (29). 

The Ni(III) oxidation state is biologically significant (101,102). Moreover, high-valent nickel species may be intermediates in some catalytic oxidations (97) and in the nickel-mediated sequence-specific oxidative cleavage of DNA by designed metalloproteins (103) as discussed in Section I,G. The chemistry of Ni(III) macrocyclic complexes has been... 

The best characterized (35-38) of the oxidized nickel dimethyl-glyoximate species is [Nilv(dmg)3]2-, which can be obtained as the diamagnetic potassium, sodium, or barium salt. Preparation of... 

The midpoint reduction potentials of the various EPR-detectable nickel species in hydrogenase are all less than 0 mV versus the standard hydrogen electrode (Table II). This is in contrast to synthetic inorganic complexes with amino acids 44), in which the oxidation of Ni(II) to Ni(III) occurs at much higher potentials (0.8-1.2 mV) and is accompanied by reorganization of the complex 45). This requires some explanation in view of the interpretation of the Ni-A EPR signal as Ni(III)(7). 

In D. gigas hydrogenase, splittings are not observed in the Ni-A and Ni-B signals from oxidized nickel centers (Fig. 4a), but are seen in the reduced Ni-C species at low temperatures (Fig. 5b) (41, 72). The splitting of Ni-C correlates with the reduced state of a [4Fe-4S] cluster (72). The spin-spin interactions observed in EPR are consistent with a distance between the nickel and iron-sulfur cluster of less than 1.2 nm (73). 

The reactor impregnated with nickel showed inferior performance again. Deactivation was observed, which was assumed to originate from coking, sintering, oxidation of the nickel or even losses of volatile nickel species. With increasing temperature, enhanced formation of by-products, namely methane and ethane, was observed in the reformate both under partial oxidation conditions and in the autothermal mode, which was attributed to thermal cracking. 

Two other Ni(CO)4 substitutes, Ni(CO)3PPh3 and Ni(COD)2/dppe, prove to be appropriate for the catalysis of tandem metallo-ene/carbonylation reactions of allylic iodides (Scheme 7)399. This process features initial oxidative addition to the alkyl iodide, followed by a metallo-ene reaction with an appropriately substituted double or triple bond, affording an alkyl or vinyl nickel species. This organonickel species may then either alkoxycar-bonylate or carbonylate and undergo a second cyclization on the pendant alkene to give 51, which then alkoxycarbonylates. The choice of nickel catalyst and use of diene versus enyne influences whether mono- or biscyclization predominates (equations 200 and 201). 

Low-valent nickel species catalyze the reaction between Grignard reagents and aryl or alkenyl sulfide in the preparation of alkylarenes, biaryls, and alkenes (see citations in Ref. ///). Wenkert et al. recently isolated compounds 132 and 133 to show that an oxidative addition occurs between diaryl sulfides and tris(tri-/ -butyl)phosphinonickel (77/). 

During the last five years a number of researches in other laboratories have added substantially to our knowledge of the interaction of carbon monoxide and carbon dioxide with oxygen at oxide surfaces, especially nickel oxide. There is support for the idea presented in the foregoing sections that these gases can produce on the surface of the oxide a species with formula CO3, but opinions differ as to its precise description and in particular the extent to which lattice oxide ions, as opposed to adsorbed oxygen ions, are involved. The more important of these researches are summarized and critically examined in this Section. 

Nickel oxide cation species with two nickel atoms also fragmented into Ni, NiO, and NiO units when reacted with CO. The adsorption energy of CO onto these... 

The origin of the initial Ni-H species in the catalysis is a source of speculation. It has been suggested that the ( / -allyl)Ni precursors react with insertion of an ethylene molecule followed by f3-W transfer (e. g., eq. (5)), while in the case of the zerovalent nickel species the ethylaluminum component could react directly either with alkyl transfer or with an intermediate Ni(CH2Cl)Cl species formed by the oxidative addition of dichloromethane, e.g., eq. (6) [3, 5, 6]. Related organopalladium compounds, e. g. ClCH2Pd(Cy2PC2H4PCy2)Cl, have been characterized by X-ray diffraction [54-56]. 

The crystal structure of bis(NN-di-isobutyldithiocarbamato)nickel(ii). [Ni(S2-CNBu 2)2], shows that nickel is approximately square planar and co-ordinated by two symmetric bidentate ligands (Ni—S = 2.20 A) the ligand symmetry approximates to 2- The reduction mechanism of a series of nickel(ii) dithiocarbamates has been investigated in DMSO at the mercury electrode it is claimed to involve a dissociation to a nickel species which is more easily reduced than the nickel(ii) dithiocarbamate. An e.p.r. study of the reversible electrochemical reduction of nickel(ii) diethyldithio-carbamates in the presence of 2,2 -bipyridyl show that a bipy radical anion is formed initially. Ligand alkylation occurs when ao -dibromo-o-xylene is added to bis-(NiV-diethyldithiocarbamato)nickel(ii). The electron-transfer properties of 16 nickel(ii) dithiocarbamate complexes have been studied in acetone at a platinum electrode. Their oxidation is difficult and irreversible the overall process is ... 

The passive films on these metals are either the conventional oxides or species such as FeOOH, which are related chemically. On nickel the film is related to NiO, on chromium to Cr203, and on titanium to Ti02. 

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