Nickel carbon filaments catalyzed

In the present macro-scale experiments the filaments have been formed following reaction of ethane with iron and iron oxides. The decomposition of ethane to elemental carbon and hydrogen is endothermic (27) and so, at first sight, it appears that the experimental results are in conflict with the above mechanism of filament growth. However, earlier work (28) has shown that the majority of carbon formed from ethane arises from the decomposition product ethylene. The latter decomposes exothermically (27) (- A H for C2H4 at 725°C is 9.2 kcal. mole- ) so that this mechanism is not contravened. A similar rationale was used by Keep, Baker and France (29) to account for the formation of carbon filaments during the nickel catalyzed decomposition of propane. 

Carbon can exist on the metal surfaces of nickel catalysts in a variety of forms. Hydrocarbon exposure to nickel crystallites at elevated temperature (> 700 K) can rapidly produce a mass of long-growing carbon filaments (1, 2) as identified in numerous experiments analyzed by transmission electron microscopy (TEM). Yet very reactive forms of surface carbon can exist, since carbon atoms chemisorbed on nickel surfaces apparently play a central role in the mechanism of several nickel-catalyzed reactions, such as hydrocarbon synthesis, (3, U, 5) hydrocarbon steam reforming, (6, 7) and hydrogenolysis (8). 

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