Quantum chemical simulation of carbon nanotube nucleation on Al₂O₃ catalysts via CH₄ chemical vapor deposition

We present quantum chemical simulations demonstrating how single-walled carbon nanotubes (SWCNTs) form, or "nucleate", on the surface of Al₂O₃ nanoparticles during chemical vapor deposition (CVD) using CH₄. SWCNT nucleation proceeds via the formation of extended polyyne chains that only interact with the catalyst surface at one or both ends. Consequently, SWCNT nucleation is not a surface-mediated process. We demonstrate that this unusual nucleation sequence is due to two factors. First, the π interaction between graphitic carbon and Al₂O₃ is extremely weak, such that graphitic carbon is expected to desorb at typical CVD temperatures. Second, hydrogen present at the catalyst surface actively passivates dangling carbon bonds, preventing a surface-mediated nucleation mechanism. The simulations reveal hydrogen's reactive chemical pathways during SWCNT nucleation and that the manner in which SWCNTs form on Al₂O₃ is fundamentally different from that observed using "traditional" transition metal catalysts. (Chemical Equation Presented).