Hydrous nickel oxides

Ponce et al. (2001) studied the oxygen reduction reaction and the oxygen evolution reaction on mixed oxides NqAl] Mn02 (0 < x < 1). The substitution of Al by Ni increases the catalytic activity, the maximum being exhibited by NiMn204. Nickel hydrous oxide and mixed Co and Ni oxides as electrocatalysts were found active towards oxygen reduction and evolution reaction (Rashkova et al. 2002). 

Surface area, pore size, and pore volume are among the most fundamentally important properties in catalysis because the active sites are present or dispersed throughout the internal surface through which reactants and products are transported. The pores are usually formed by drying or calcining precipitates of hydrous oxides however, some materials possess porosity naturally, as in the case of carbons, natural zeolites, and others. Raney nickel catalysts... 

Hydrous sodium titanate was prepared by the method of Dosch and Stephens (1). Titanium isopropoxide was slowly added to a 15 wt% solution of sodium hydroxide in methanol. The resulting solution was hydrolyzed by addition to 10 vol% water in acetone. The hydrolysis product is an amorphous hydrous oxide with a Na Ti ratio of 0.5 which contains, after vacuum drying at room temperature, approximately 13.5 wt% water and 2.5 wt% residual alcohol. The ion-exchange characteristics of the sodium titanate and the hydrolysis behavior of the nickel nitrate solutions were characterized using a combination of potentiometric titrations, inductively coupled plasma atomic emission (ICP) analysis of filtrates, and surface charge measurements obtained using a Matec electrosonic amplitude device. 

Nickel is deposited quantitatively from ammoniacal solutions, incompletely from weakly acidic solutions, and not at all from strongly acidic ones. (A quantitative separation of copper from nickel requires that the acid concentration be kept high.) Among the important interferences in the determination of nickel are silver, copper, arsenic, and zinc, which can be removed by precipitation with hydrogen sulfide. Iron(II) and chromates are objectionable, but can be removed by precipitation of the hydrous oxides. 

The silica may also be contaminated by metallic impurities such as aluminum, nickel, and iron, depending on the synthesis of the silica or the manufacturing process. These metals may be present either in the form of oxides and hydrous oxides or through oxygen bonds attached to an Si atom [3]. The metal impurities may also have an effect on the chromatography, causing peak tailing due to complexation with the trace metal impurities. The acidity of the surface silanols is increased with the presence of these metal impurities. 

Coprecipitated NiO-AljOi samples are typical of a wide variety of dual hydrous oxide gels. They are precursors to reduced Ni/AIjO) catalysts used in hydrogenation and methanation. Although these catalysts are produced by other routes, the intimate interactions fostered by coprecipitation are believed to impart improvements in activity and stability to the nickel crystallites/ although mechanical strength is lower. It may also be possible that irreducible compounds of NiO and AljOj, facilitated by coprecipitation, play some role in forming stable promoters. 

Both nickel and aluminum precipitate hydrous oxide sols. For best combinations, care must be taken to ensure that precipitation occurs simultaneously. Variations of pH within the vessel or during addition of the alkali result in preferential precipitation of one component, yielding product nonuniformity. One laboratory approach is to use the apparatus shown in Fig. 6.I1. ... 

In view of their major application in aqueous battery systems more work has been carried out on the structural aspects of the oxides of these two metals than any of the systems discussed earlier. Details of the structure and reactivity of the nickel oxide battery materials can be found in recent reviews by Briggs209 and Oliva et al.2 Both hydrous and anhydrous phases exist for both the Ni(II) hydroxide and Ni(III) oxyhydroxide systems. Most interesting are the comments of Le Bihan and Figlarz,210 and McEwen,211 with regard to turbostatic structures the latter are found in materials where the ordering of the oxide is quite limited, i.e., the systems consist of highly ordered nuclei linked in a disordered manner—the latter feature should certainly enhance mass transfer processes and may well be involved in many other hydrous oxide systems. 

Nickel laterite is nickel mineral changed by weathering, etching, enrichment, and then it turns loose clay-like, composed of iron, aluminum, silicon, and some hydrous oxides. The element and moisture content are rich in this kind of ore. The elemental composition and content (Table 1) can be obtained by XRF elemental analysis and chemical analysis.XRD demonstrated that host minerals of the iron-enriched and magnesium-depleted version of laterites are mainly ferric iron oxides, typically goethite, FeO(OH), and nickel embedded in the mineral is mainly as the pattern of NiO (Figure 1). All of the samples came from Baosteel. 

When the test for nickel is to be carried out in ammoniacal solution, and other metals, precipitable by ammonia, are present, the hydrous oxide precipitation must be prevented by the addition of citrates or tartrates. 

In the same way, 0.032 y nickel can be detected in the presence of 4800 times the amount of iron. The iron is fixed in the center of the fleck as Fe hydrous oxide, while the nickel ammine salt diffuses outward and reacts with rubeanic acid in a separate zone. 

In the years since the discovery of nickel and iron in the catalytic centres, numerous different descriptions of the catalytic cycle of hydrogenase have been proposed. These were based on different oxidation states of the metal centres, and different sequences of transfer of electrons and hydrous. Although the reaction cycle has not been definitively resolved, the spectroscopic evidence places constraints on possible models that should be considered. 

Precipitation can remove soluble nickel Ifom water. In aerobic waters, nickel ferrite is the most stable compound (Rai and Zachara 1984). Nickel may also be removed by coprecipitation with hydrous iron and manganese oxides. Nickel removed by precipitation and coprecipitation settles into the sediment. 

Led by the deep green color of its solutions to suspect the presence in it of copper, Proust passed hydrogen sulfide into an acidic solution of tire iron, but obtained no precipitate. Believing that only nickel could produce such an effect, he removed the iron as hydrous ferric oxide and prepared nickel sulfate from the filtrate. These experiments are described in Nicholsons Journal for November, 1800 The native iron of Peru is... 

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