Oxygen, interactions with nickel

We shall not discuss here oxygen interaction with nickel since, although it is one of the most extensively studied systems (59), there is still considerable ambiguity and confusion regarding possible models. Two systems that, however, have lent themselves to investigation by XPS are the oxidation of lead (60, 60a) and aluminum surfaces (10). In both cases substantial shifts were observed in the metal core levels, which as emphasized previously is more the exception than the rule. 

Fig. 6.16. Kinetics of emission of O-atoms during interaction of oxygen with nickel films...

A cyclization reaction involving a half-formed bridge in which alkyl halide functions interact with (initially) coordinated oxygen atoms is illustrated by [2.9] (Kluiber Sasso, 1970). The X-ray structure of the red paramagnetic nickel complex (65) indicates that the macrocycle coordi-... 

As seen from Scheme 7.2, the epoxy-ring cleavage and nickel oxidation proceed simultaneously. The nickel-oxygen bond is formed. This results in the formation of the carbon-nickel biradical in which Ph-CH fragment can rotate freely. The cleavage of the (NiO)-C bond leads to the formation of a mixture of styrenes. At early reaction stages (30 min), cis and trans olefins are formed in 50 50 ratio. After a prolonged contact (30 h), when all possible transformations should be completed, the trans isomer becomes the main product and cis trans ratio becomes 5 95. Such enrichment of the mixture with the trans isomer follows from the formation of the di-P-(trimethylsilyl)styrene anion-radical and its isomerization. The styrene formed interacts with an excess of the nickel complex. 

In Fig. 26, for example, the surface is covered with carbon monoxide (6 = 0.89). If at Ao, oxygen gas at 6.1 X 10 mm. Hg pressure is admitted, its molecules are still adsorbed under pressure to a covering of 6 = 0.02 however no further increase in resistance is observed and the oxygen can be pumped off completely. At a pure nickel surface an oxygen pressure of 6.1 X 10 mm. Hg would lead to a resistance increase of 5.6%. Apparently the carbon monoxide layer of d = 0.89 blocks the surface so completely that at 90.4°K. oxygen molecules do not dissociate into atoms, which could interact with the electron gas of the metal. 

The hypothesis of formation of oxygenated compounds as intermediate products was rejected by Eidus on the basis of experiments on the conversion over cobalt of methyl and ethyl alcohols and formic acid which were found to form carbon monoxide and hydrogen in an intermediate step of the hydrocarbon synthesis (76). Methylene radicals are thought to be formed on nickel and cobalt catalysts (76) by hydrogenation of the unstable group CHOH formed by interaction of adsorbed carbon monoxide and hydrogen, while on iron catalysts methylene radicals are probably formed by hydrogenation of the carbide (78,81). Carbon dioxide was found to interact with the alkaline promoters on the surface of iron catalysts as little as 1 % potassium carbonate was found to occupy 30 to 40% of the active surface area. The alkali also promotes carbide formation and the synthesis reaction on iron (78). 

When 2 interacts with Ni(BF4)3, 2 is coordinated in a distorted octahedral fashion to the Ni2+ with trans oxygen atoms, and a diethylene S-O-S linkage that is meridional. All six donor atoms are bound to the nickel center. The crystal is racemic with four pairs of enantiomers per unit cell. In the structure, the two Ni-O bonds average 2.068(7) A in length, while the four Ni-S bonds average 2.370(3) A. 

As structurally different as they are, nonetheless oxygen and aryl bromides bear interesting resemblances, in that their interaction with aryl-methyl-nickel compounds la and b both lead to the elimination of aryl and methyl groupsT For"purposes of further discussion, we propose a charge transfer interaction Common to both, in which reactions are promoted by a prior electron transfer from I to oxygen or aryl bromide acting as electron acceptors (A). ... 

Ni0.03Mgo.97O solid solution catalyst has high resistance to carbon deposition in COj reforming of methane. From the characterization results, this catalyst was found to have highly dispersive nickel metal particles with the interaction with support surface. The inhibition mechanism is suggested to be the activation of adsorbed COj at the interface between metal and support surface and rapid supply of oxygen species to nickel surface. 

Table 9.1 Comparison of data pertaining to the interaction of oxygen with nickel surfaces in the chemisorption and oxide film growth regimes...

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