Formation of carbon nanofilaments from C6-C16 alkanes over nickel-containing catalysts

The properties of 85%Ni/Al₂O₃ and NiO/Sibunit series catalysts have been studied in the formation of carbon nanofilaments from n-hexane, n-undecane, and n-hexadecane. In the temperature range 450–600°C, the reactivity of these hydrocarbons decreases in the following order: n-hexane > n-undecane > n-hexadecane. The deposition rate of carbon nanofilaments from n-hexane or n-undecane over the 85%Ni/Al₂O₃ catalyst in the range 450–600°C slightly depends on the reaction temperature. The activation energy of the formation of carbon nanofilaments from n-hexane is 10 kcal/mol and that from n-undecane, 13.5 kcal/mol. The rate-limiting reaction is the interaction of a paraffin molecule with the nickel metal surface. As the reaction temperature increases to 700°C, the formation rates of carbon nanofilaments from the C₆-C₁₆ paraffin hydrocarbons are equalized, which is associated with the increase in the intensity of thermal pyrolysis reactions of alkanes. The resulting olefins, first of all, ethylene and propylene, become major contributors to carbon formation.