Insights into the reaction process and mechanism of CNTs growth from n-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 n-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.