Nickel atomic processes

The ionic current intensity corresponding to the peak at 169 amu was analyzed under isothermal and polythermal conditions [383]. It was found that in a gaseous atmosphere, the intensity changes are in correlation with the CO content and in negative correlation with the C02 content. The presence of CO in vacuum systems equipped with heating elements is usually related to thermo-cycling and desorption of CO by nickel atoms [386]. Based on the above, the presence of NbF4+ ions in mass spectra is most probably related to the niobium reduction process, which can be represented as follows ... 

Although, as has already been mentioned, under matrix conditions between 10 and 77 K, there is no oxidative addition of a chloroolefin to nickel or palladium atoms (141), it is evident that this is simply a function of reaction and processing conditions, as it has been shown (68) that oxidative addition to C-C or C-H bonds by nickel atoms leads to pseudocomplexes having Ni C H ratios of 2-5 1 2. Klabunde and co-workers investigated the oxidative addition-reactions of palladium atoms with alkyl halides (73) and benzyl chlorides (74). 

In one example of an asymmetric codimerization, a pronounced effect on the optical yield has been observed by increasing the phosphine/nickel molar ratio (94, 95). This effect may be ascribed to suppression of a dissociation process or to complexation of a second molecule of the inducing phosphine to the nickel atom. 

Powder Formation. Metallic powders can be formed by any number of techniques, including the reduction of corresponding oxides and salts, the thermal dissociation of metal compounds, electrolysis, atomization, gas-phase synthesis or decomposition, or mechanical attrition. The atomization method is the one most commonly used, because it can produce powders from alloys as well as from pure metals. In the atomization process, a molten metal is forced through an orifice and the stream is broken up with a jet of water or gas. The molten metal forms droplets to minimize the surface area, which solidify very rapidly. Currently, iron-nickel-molybdenum alloys, stainless steels, tool steels, nickel alloys, titanium alloys, and aluminum alloys, as well as many pure metals, are manufactured by atomization processes. 

These results led the workers to suggest that catalysis actually leads to the removal of surface nickel atoms, primarily due to local heating which takes place at the reaction site. Furthermore, during the catalytic process, the nickel atom is temporarily part of a liquid- or gas-phase intermediate. Once the catalytic process is complete, the authors postulated that the free nickel atom readsorbed onto the bulk nickel, adsorbed onto the inert support, remained as nickel sol in the liquid, or continued to act as a catalyst. It was claimed that this model explained several observations, such as the differences between unsupported and supported nickel. The supported metal has a greater surface area upon which the metal can readsorb, so it tends to leave fewer atoms in the product liquid. The model also explains the observation that the reaction vessel became coated with a thin film of nickel after lengthy use. This postulated etching mechanism is similar to the recent model discussed above, whereby etching results from free-radical-surface interactions. 

Previous results(2) had shown that a Pd-Ni-SMM catalyst was effective for hydrocracking hexane as well as a raffinate feed. Conclusions showed that this catalyst system when containing two nickel atoms per unit cell (15 wt % nickel) was approximately 15 times more active than a Pd-rare earth-Y zeolite catalyst and 1.2 times more active than Pd-H-mordenite. This same catalyst system (0.7 wt % Pd-15 wt % Ni-SMM) was chosen for our raffinate processing studies. 

A large number of intermediate pathways arc possible when catalytic reactions interfere with the polymerization-dehydrogenation steps. A common scenario is the catalytic dehydrogenation of hydrocarbons on nickel surfaces followed by dissolution of the activated carbon atoms and exsolution of graphene layers after exceeding the solubility limit of carbon in nickel. Such processes have been observed experimentally [40] and used to explain the shapes of carbon filaments. In the most recent synthetic routes to nanotubes [41] the catalytic action of in situ-prepared iron metal particles was applied to create a catalyst for the dehydrogenation of cither ethylene or benzene. 

Complex surface processes during HC1 etching (acidic dissolution of oxides, electrochemical oxidation) lead to the formation of a porous, chloride-containing iron oxide layer while nickel remains in the zero-valent state. Subsequent reduction, facilitated also by hydrogen atoms formed on nickel sites, results in an increased number of surface iron and nickel atoms and an enhanced catalytic activity. The larger concentration of atomic hydrogen on the surface and the presence of surface Ni are observations that are supported by the decreased selectivity of olefin formation. 

The hydrogen transfer preferably takes place coplanar to the q -allyl and the alkyl groups of the Cm chain, with the shifted hydrogen atom residing in square-planar conformation together with the two groups. The process occurs with the displacement of the inner olefinic double bond, which is coordinated in 5, from the immediate proximity of the nickel atom by the shifted hydrogen... 

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