Branching carbon nanotubes were synthesized by pyrolysis of acetylene at 700℃ over oxygen free copper and γ Al2O3 supported Cu unitary or Cu/Fe binary catalysts. The morphologies of the as grown products were characterized by transmission electron microscopy. The results indicated that the branching structures were closely related to the Cu component of the catalysts. We proposed that the special electronic structure (3d104s1) of Cu play the crucial role in the formation of the heptagon defects related to the branching structures.
