Nickel oxalate

Other simple nickel salts of organic acids include the oxalate [20543-06-0] oleate [68538-38-5], and stearate [2223-95-2]. The latter two have been used as oil-soluble nickel forms in the dyeing of synthetic polyolefin fibers (see Driers and metallic soaps). Nickel oxalate has been used as a catalyst intermediate (59). 

Nickel Oxalate. This salt, NiC204, mol wt 146.7, is produced as a greenish white crystalline dihydrate [6018-94-6]. It decomposes by heating at 320°C under vacuum into Ni metal and carbon dioxide. Nickel oxalate is used for the production of nickel catalysts and magnetic materials. 

Kadlec and Rosmusova [1153] believe that both Ni and Co oxalates initially yield product oxide and that the proportion of metal increases with a. Since nickel oxalate decomposes at temperatures 60 K lower than those for CoC204, even a small proportion of Ni2+ markedly increases the rate of decomposition of cobalt oxalate. The effect was attributed to the catalytic properties of the preferentially formed Ni metal. The a—time curves were generally sigmoid and showed only slight deviations in shape with changes in the Ni Co ratio. In the decomposition of a mechanical... 

C 4 g catalyst, H20/EtOH = 3 Liquid Catalysts were prepared by impregnation using nickel oxalate as a Ni precursor, flow rate = 0.05 ml/min The activity, stability and H2 selectivity decreased in the order Ni/La203 > Ni/... 

Nickel Oxalate. This salt is pioduced as a greenish white ciystalline dihydrate. Nickel oxalate is used for the production of nickel catalysts and magnetic materials. 

Nickel oxalate, similarly to nickel formate, decomposes to give finely divided nickel powder with the liberation of carbon dioxide containing a trace of carbon monoxide at about 200°C. However, it has not been widely used industrially because of the higher cost of the oxalate.31... 

Likewise, the direct synthesis of [M(PF3)4] (M = Ni, Pd, Pt) complexes has been achieved from the appropriate metal powder (method F), or alternatively under very mild conditions from highly reactive forms of the metal (e.g., Ni) generated either from the decomposition of nickel oxalate or nickel tetracarbonyl or activated by sulfide (method G). 

Non-isothermal kinetic studies [69] of the decomposition of samples of nickel oxalate dihydrate doped with Li and Cr showed no regular pattern of behaviour in the values of the Arrhenius parameters reported for the dehydration. There was evidence that lithium promoted the subsequent decomposition step, but no description of the role of the additive was given. 

Jacobs and Tariq Kureishy [48] identified three stages in the decomposition of nickel oxalate a surface reaction, a period of slow development of nuclei and finally the growth of these nuclei at constant rate during which the interface advances through the bulk of the reactant crystallites. 

The thermal decmnpositions of mixed magnesium-nickel oxalates [77] commenced at sites of incorporation of cations of the additive into the oxalate lattice, regardless of the relative stabilities of the oxalates concerned. A ftuther study compared the behaviour of magnesium-cobalt and magnesium-nickel oxalates [55]. 

Carboxylate decompositions are generally irreversible and it is noteworthy that compensation behaviour, a pattern of behaviour frequently associated with reversible processes, is not a feature of the literature concerned with these reactants. More usually the values for carboxylate decompositions are accepted as approximating to a constant value. For example, seven values of reported for the decomposition of nickel oxalate (134, 135, 136, 150, 150, 168 and 177 kJ mol ) were (with one exception) all within 151 17 kJ mol, which is typical of the reproducibility found in this field. Greater variation may arise when the decomposition is influenced by other reactions, such as prior dehydration [112]. 

Using DTA measurements, Macklen [148] compared the temperatures of onset of decomposition of manganese, iron, cobalt and nickel oxalates for reactions in nitrogen and in air. The reactivities of these salts follows the sequence of ease of cation oxidation [152] (IvP — and from this it was concluded that the first step for reaction in air is cation oxidation followed by rapid breakdown of the oxalate anion. 

The initial or rate limiting step for anion breakdown in metal oxalate decompositions has been identified as either the rupture of the C - C bond [4], or electron transfer at a M - O bond [5], This may be an oversimplification, because different controls may operate for different constituent cations. The decomposition of nickel oxalate is probably promoted by the metallic product [68] (the activity of which may be decreased by deposited carbon, compare with nickel malonate mentioned above [65]). No catalytically-active metal product is formed on breakdown of oxalates of the more electropositive elements. Instead, they yield oxide or carbonate and reactions may include secondary processes [27]. There is, however, evidence that the decompositions of transition metal oxalates may be accompanied by electron transfers. The decomposition of copper(II) oxalate [69] (Cu - Cu - Cu°) was not catalytically promoted by the metal and the acceleratory behaviour was ascribed to progressive melting. Similarly, iron(III) oxalate decomposition [61,70] was accompanied by cation reduction (Fe " - Fe ). In contrast, evidence was obtained that the reaction of MnC204 was accompanied by the intervention of Mn believed to be active in anion breakdown [71]. These observations confirm the participation of electron transfer steps in breakdown of the oxalate ion, but other controls influence the overall behaviour. Dollimore has discussed [72] the literature concerned with oxalate pyrolyses, including possible bond rupture steps involved in the decomposition mechanisms... 

More detailed experiments with copper and nickel oxalates (184) confirmed the extensive decomposition under radiation, although the doses required to reach 80 to 90% metal appeared to be somewhat larger (perhaps by a factor of 2 to 3) than in the previous work (183). This could easily arise from differences in the techniques or in the materials. A preliminary irradiation insufficient to cause appreciable decomposition by itself (ca. 4 x 10 2 ev/gm) reduced the induction period and increased the rate of a subsequent thermal decomposition. There is considerable work on the effects of irradiation upon subsequent thermal decomposition of various solids, although not with catalyst preparation in mind (132h, 185-188). In the case of CaO, irradiation of the parent material, Ca(OH)2, did not affect the area of the oxide, although irradiation of the latter (with copper X-rays) decreased the specific surface for samples calcined (before irradiation) between 400 and 900°. 

At higher gas pressures, a buoyancy correction must be made to allow for the volume occupied by the sample this increases with pressure. The mass of gas displaced is given by MPV/RT, where P and V are pressure and volume of gas of molar mass M, and/ is the gas constant. During reactant decompositions, the volume of the residual sample changes for example, the nickel metal product formed on heating nickel oxalate dihydrate occupies only about 10% the volume of the reactant from which it was formed. Other corrections include the contributions from any gas flow in and around the balance mechanism and the effects of convection that increase with pressure. Some specific issues are discussed in the following text ... 

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