Ni–SiO2 and Ni–Fe–SiO2 catalysts for methane decomposition to prepare hydrogen and carbon filaments

Active and stable Ni–Fe–SiO2 catalysts prepared by sol–gel method were employed for direct decomposition of undiluted methane to produce hydrogen and carbon filaments at 823 K and 923 K. The results indicated that the lifetime of Ni–Fe–SiO2 catalysts was much longer than Ni–SiO2 catalyst at a higher reaction temperature such as 923 K, however, a reverse trend was shown when methane decomposition took place at a lower reaction temperature such as 823 K. XRD studies suggested that iron atoms had entered into the Ni lattice and Ni–Fe alloy was formed in Ni–Fe–SiO2 catalysts. The structure of the carbon filaments generated over Ni–SiO2 and Ni–Fe–SiO2 was quite different. TEM studies showed that “multi-walled” carbon filaments were formed over 75%Ni–25%SiO2 catalyst, while “bamboo-shaped” carbon filaments generated over 35%Ni–40%Fe–25%SiO2 catalysts at 923 K. Raman spectra of the generated carbons demonstrated that the graphitic order of the “multi-walled” carbon filaments was lower than that of the “bamboo-shaped” carbon filaments.