Agglomerated CNTs synthesized in a fluidized bed reactor: Agglomerate structure and formation mechanism Original Research Article

Agglomerated carbon nanotubes (CNTs) were synthesized by catalytic pyrolysis of propylene on Fe/Mo/Al2O3 catalysts in a nano-agglomerate fluidized-bed reactor (NAFBR) of 196 mm I.D. The macroscopic properties and microstructure of the CNTs and their evolution were systematically characterized by high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. The CNTs from the NAFBR are sub-agglomerates entangled with each other. Their formation involves the initial fragmentation of the catalyst support, sub-agglomerate formation and expansion of the agglomerates due to CNT growth. When the structure of the catalysts is destroyed, the release of stress inside the catalyst particles will result in structural defects in the CNT shells. More perfect CNTs are obtained in fully developed agglomerates. A model is proposed to explain the process of agglomerate formation and based on its formation mechanism, an approach to control CNT quality in an NAFBR is proposed.