Carbon Dioxide Promotes Dehydrogenation in the Equimolar C2 H2 -CO2 Reaction to Synthesize Carbon Nanotubes

Abstract

The equimolar C₂ H₂ -CO₂ reaction has shown promise for carbon nanotube (CNT) production at low temperatures and on diverse functional substrate materials; however, the electron-pushing mechanism of this reaction is not well demonstrated. Here, the role of CO₂ is explored experimentally and theoretically. In particular, ¹³ C labeling of CO₂ demonstrates that CO₂ is not an important C source in CNT growth by thermal catalytic chemical vapor deposition. Consistent with this experimental finding, the adsorption behaviors of C₂ H₂ and CO₂ on a graphene-like lattice via density functional theory calculations reveal that the binding energies of C₂ H₂ are markedly higher than that of CO₂ , suggesting the former is more likely to incorporate into CNT structure. Further, H-abstraction by CO₂ from the active CNT growth edge would be favored, ultimately forming CO and H₂ O. These results support that the commonly observed, promoting role of CO₂ in CNT growth is due to a CO₂ -assisted dehydrogenation mechanism.

Keywords: carbon dioxide; carbon nanotubes; chemical vapor deposition; dehydrogenation; growth mechanism.