Insights into the reaction process and mechanism of CNT growth from <i>n</i>-hexane on Fe-based catalysts

Due to their outstanding physicochemical properties, carbon nanotubes (CNTs) have been widely studied and applied in the nanoscience and nanotechnology fields. Herein, Fe-based catalysts were prepared by the impregnation method using Al₂O₃, SiO₂, ZrO₂, TiO₂ and SnO₂ supports and were used for CNT synthesis from <i>n</i>-hexane under different reaction times and temperatures. It was found that the metal-support interaction and Fe₂O₃ particle size of Fe-based catalysts regulated CNT growth. The moderate metal-support interaction of Fe-Al₂O₃, Fe-SiO₂ and Fe-ZrO₂ was suitable for CNT synthesis: Fe-Al₂O₃ and Fe-SiO₂ produced 383.2-494.6 mg g^-1 CNTs with a diameter of 23.3-26.4 nm, while Fe-ZrO₂ exhibited a lower CNT yield of 141.8 mg g^-1 with a larger diameter of 49.3 nm. Fe-TiO₂ metal-support interaction was too strong, and the SnO₂ support exhibited strong reducibility, both of which inhibited CNT synthesis. Since Fe₂O₃ particle stepwise participated in CNT synthesis in the activity order, it led to an increased quantity but a decreased formation rate of CNTs with prolonged reaction time, which could be compensated by increasing the reaction temperature.