Formation of Carbon from High-Molecular Hydrocarbons on Iron Subgroup Metals on the Sibunite Carbon Support

Abstract

The properties of iron subgroup metals (Fe, Co, Ni) on a mesoporous carbon Sibunite support during the formation of carbon in the catalytic pyrolysis of high-molecular alkanes (hexane, undecane, and hexadecane) were studied. In the case of the NiO/Sibunite catalyst, the rate of carbon formation at temperatures of 500–600^оС decreased in the series hexane > undecane > hexadecane. Carbon is deposited in the form of carbon nanofibers. The activity series of reduced catalysts in carbon formation was determined: 10%NiО/Sibunite > 10%CoО/Sibunite > 10%Fe₂О₃/Sibunite. The morphology of carbon that formed on the 10%CoО/Sibunite catalyst depends on the particle size of the active component: multiwalled carbon nanotubes (MCNTs) grow on particles of 10–30 nm, and carbon nanofibers grow on particles larger than 30 nm. The X-ray diffraction studies of Fe₂O₃/Sibunite after the reaction showed that the active component can be in the form of metal or iron carbide, the fraction of each phase in the catalyst depending on the particle size of the active phase. For particles of 10–30 nm, iron is in the form of metal, for larger particles, it is in the form of carbide. It was concluded that iron carbide particles are responsible for the formation of carbon nanofibers, and iron particles are responsible for the formation of MCNTs.