Catalytic decomposition of light alkanes, alkenes and acetylene over Ni/SiO2

The decomposition of different hydrocarbons (CH₄, C₂H₆, C₂H₄, C₂H₂, C₃H₈, and C₃H₆) over Ni (5 wt.%)/SiO₂ catalysts was carried out. The initial rates of decomposition of the hydrocarbons, the kinetic curves of the decomposition and the kinetic curves of the hydrogenation of deposited carbon into methane depended on the types of hydrocarbons. In addition, the catalytic life of the Ni/SiO₂ catalyst was also dependent on the types of hydrocarbons, i.e. the life was longer according to the order, alkanes>alkenesacetylene.

The carbons deposited on the catalyst were characterized by SEM and Raman spectroscopy. The appearances of the deposited carbons were different among alkanes, alkenes, and acetylene, i.e. a zigzag fiber structure from methane, and a rolled fiber structure from alkenes and acetylene. From Raman spectra of the deposited carbons, it was found that the degree of graphitization of deposited carbon was higher in the order, alkanes>alkenes>acetylene. These results suggest that the mechanism of decomposition of hydrocarbons and the growth mechanism of carbon fibers on the catalyst were different among alkanes, alkenes and acetylene.