Cobalt, hydrogenation activation energy

For illustration purposes, we briefly discuss oxygen removal on cobalt. The Fischer-Tropsch reaction on this catalyst is known to be only weakly suppressed by the product water (41). The available computational results indicate that the activation energy for the reaction of adsorbed hydrogen, Hads/ with Oads to adsorbed OH species, OHads/ on cobalt is about 166 kj/mol for the flat Co(OOOl) surface and 70 kj/mol for sfepped cobalf surfaces (42). For comparison, fhe activation energy for fhis reaction on rhodium is 90 kJ/mol (43) Subsequent water formation occurs by recombination of OHads with Hads this reaction has a barrier of befween 5 and 10 kj/mol. 

The observed activation energy of 15 kcal for this reaction implies a considerable stability for the AgH+ species. The catalytic properties of cobalt cyanide solutions in hydrogenation reactions have been described in Section III,F see also 195, 195a). 

The identification of catalytically active species in FTS is of fundamental importance, as an improved understanding could enable the development of catalysts with increased activity and selectivity. In cobalt- and ruthenium-catalysed FTS, metallic cobalt and ruthenium function as active catalysts. However, in iron-catalysed FTS there are several distinct species generated during the reaction. Due to the lower, or similar, activation energy for iron carbide formation in comparison to carbon monoxide hydrogenation, iron-carbide formation is typically observed in FTS. The formation of several iron-carbide phases have been observed -Fe2C/8 -Fe2.2C (hexagonal... 

From 1974 onwards, Rh-based hydroformylation became industrial. The use of a catalyst metal that is about 1000-times more expensive than cobalt was driven by several reasons. First, Rh-hydroformylation is more active and thus requires much lower process pressures (lower energy consumption in compression units) and smaller reactors. Second, Rh-hydroformylation shows a very high selectivity to the aldehyde product with only minimal hydrogenation activity being observed. This is of particular importance for propylene hydroformylation where butyl alcohol is not the principle market use. In contrast, for the desired end-use of w-butyraldehyde in the form of its aldol condensation product 2-ethylhexanol a pure aldehyde feed is required as hemiacetals (formed by reaction of aldehyde and alcohol) complicate product purification and add to operating costs. 

The activation energy in Eqs. 1.13 and 1.14 is lower than the activation energy of monomolecular degradation of hydrogen peroxides. Thus the oxidation of plastics is accelerated by the presence of metal ions. Relevant metal ions include iron (Fe y Fe " ), cobalt (Co yCo ), copper (CuyCu ), chromium (Cr yCr ), manganese... 

In yet another method [42], the reaction for pyrolysis of l,2-dichloro-2,2-difluoroethane in the presence of hydrogen was carried out in the absence of a catalyst in an essentially empty reactor at a temperature >400°C. In the absence of a catalyst refers to the absence of a conventional catalyst. A typical catalyst has a specific surface area and is in the form of particles or extrudates, which may optionally be supported to facilitate the dehydrochlorination reaction by reducing its activation energy. The reactors that are suitable are quartz, ceramic (SiC), or metallic reactors. In this case, the material constituting the reactor was chosen from metals such as nickel, iron, titanium, chromium, molybdenum, cobalt or gold, or alloys thereof. The metal, chosen more particularly to limit corrosion or other catalytic phenomena, may be bulk metal or metal plated onto another metal. 

Compensation behavior found for the decomposition of hydrogen peroxide on preparations of chromium (III) oxide, which had previously been annealed to various temperatures, was attributed to variations in the energy states of the active centers (here e 0.165). Compensation behavior has also been observed (284) in the decomposition of hydrogen peroxide on cobalt-iron spinels the kinetic characteristics of reactions on these catalysts were ascribed to the electronic structures of the solids concerned. 

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