Ni-SiO_2 and Ni-Fe-SiO_2 catalysts for methane decomposition to prepare hydrogen and carbon filaments

摘要

Active and stable Ni-Fe-SiO_2 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-SiO_2 catalysts was much longer than Ni-SiO_2 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-SiO_2 catalysts. The structure of the carbon filaments generated over Ni-SiO_2 and Ni-Fe-SiO_2 was quite different. TEM studies showed that "multi-walled" carbon filaments were formed over 75%Ni-25%SiO_2 catalyst, while "bamboo-shaped" carbon filaments generated over 35%Ni-40%Fe-25%SiO_2 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.