Porous and Lamella-like Fe/MgO Catalysts Prepared under Hydrothermal Conditions for High-Yield Synthesis of Double-Walled Carbon Nanotubes

Hydrothermal treatments are used to reform Fe/MgO catalysts into lamella-like Fe/Mg(OH) 2 catalysts, resulting in specific surface areas (SSAs) of more than 100 m 2 /g. Porous and lamella-like Fe/MgO catalyst can be obtained under the reaction condition. In the materials prepared by CH 4 cracking at 850 °C over the hydrotherm-treated catalysts, more than 70% of the nanotubes are found to be double-walled carbon nanotubes (DWNTs). With the catalyst after a 180−220 °C hydrothermal treatment, a high purity of DWNTs and a yield up to nearly 3 times that obtained with the original catalyst are achieved at the same reaction condition, as characterized by scanning electron microscope, thermogravimetric, and Raman analysis. The porous structure with high surface area of the hydrotherm-treated catalysts and the good dispersion of Fe species on Mg(OH) 2 layers are considered as the main factors for the improvement of nanotube yield. Considering the good hydrophilicity of MgO, hydrothermal treatments are promising in being applied to other metal catalysts supported by hydrophilic oxides.