Nickel 3 2+dissociation

Carbon monoxide is dissociatively adsorbed on the surfaces of those metals, such as iron or cobalt, which are active in hydrocarbon synthesis. On nickel, dissociation also occurs, although at higher temperatures than on iron. Chain... 

Beebe T P, Goodman D W, Kay B D and Yates J T Jr 1987 Kinetics of the activated dissociation adsorption of methane on low index planes of nickel single crystal surfaces J. Chem. Phys. 87 2305... 

The use of CO is complicated by the fact that two forms of adsorption—linear and bridged—have been shown by infrared (IR) spectroscopy to occur on most metal surfaces. For both forms, the molecule usually remains intact (i.e., no dissociation occurs). In the linear form the carbon end is attached to one metal atom, while in the bridged form it is attached to two metal atoms. Hence, if independent IR studies on an identical catalyst, identically reduced, show that all of the CO is either in the linear or the bricked form, then the measurement of CO isotherms can be used to determine metal dispersions. A metal for which CO cannot be used is nickel, due to the rapid formation of nickel carbonyl on clean nickel surfaces. Although CO has a relatively low boiling point, at vet) low metal concentrations (e.g., 0.1% Rh) the amount of CO adsorbed on the support can be as much as 25% of that on the metal a procedure has been developed to accurately correct for this. Also, CO dissociates on some metal surfaces (e.g., W and Mo), on which the method cannot be used. 

Nickel carbonyl has been shown to have a very high retention— 98.7%—both in the pure hquid and as 10% solution in n-heptane. It was argued that this represents the results following essentially complete isotopic exchange. Since the exchange of CO with Ni(CO)4 is known to occur quite rapidly by a dissociation mechanism, reformation of nickel carbonyl following the nuclear reaction would proceed rapidly by the reaction... 

Methane is a stable molecule and therefore hard to activate. As a result the sticking probability for dissociative chemisorption is small, of the order of 10 only, and ruthenium is more reactive than nickel. However, a stretched overlayer of nickel is significantly more active than nickel in its common form, in agreement with expectation. 

Figure 6.41. Reactivity of a pseudomorfic overlayer of Ni deposited on Ru(OOOl) for the dissociative adsorption of methane. At zero coverage the measurements reveal the sticking of methane on pure Ru. When nickel atoms are deposited on the surface, the dissociation...

It has been pointed out that the types of solvents which are used here, are not generally such as would enter into strong association with the substrate. The molecularity of the substitution reaction may then stand more chance of being an operational concept. Amongst the binary carbonyls, the only systems which have been extensively studied have been nickel tetracarbonyl and the hexacarbonyls of group VI. For the former, the observation of a first-order rate is at least consistent with a rate-determining dissociation of one carbonyl ligand followed by reaction of the intermediate with whichever nucleophile should be available. 

The bond dissociation energy of fluoromethane is 115 kcal mol , which is much higher than the other halides (C-Cl, C-Br and C-1, respectively 84, 72 and 58 kcal mol ) [6], Due to its strength, the carbon-fluorine (C-F) bond is one of the most challenging bonds to activate [7], A variety of C-F bond activation reactions have been carried out with different organometallic complexes [8], Among them, nickel [9] and ruthenium complexes have proven to proceed selectively under mild conditions [10],... 

The group at Aarhus have reported carbon-induced structures at Ni(lll) and Ni(110) surfaces resulting from the dissociation of ethylene at high temperatures.27 Between 400 and 500 K, the Ni(l 10) surface is seen to form two carbidic structures with (4 x 3) and (4 x 5) domains present arising from surface reconstruction with substantial transport of nickel taking place. At higher temperatures (560 K), the surface becomes dominated by the (4 x 5) structure, which is well ordered and can be observed clearly by LEED. Ion scattering studies provide additional information which enables models to be constructed for both the (4 x 3) and (4 x 5) phases. 

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