Abstract
<jats:p>Carbon nanotubes (CNTs) are key carbon nanomaterials for a range of energy-related applications. The performance of these applications strongly depends on the electrothermal properties of CNTs, which are governed by the structure developed during synthesis. Here, we investigate how early-stage chemical reactions evolve for different hydrocarbon precursors and how carrier gas and reactor-environment effects influence CNT formation in floating-catalyst chemical vapour deposition (FCCVD). In this work, experimental observations were correlated with reactive molecular dynamics (MD) simulations of early-stage reaction pathways, as well as FEM and CFD simulations of temperature distributions and gas-flow behaviour inside the reactor. FEM/CFD modelling revealed spatially confined growth zones and reactor-scale thermal asymmetries that strongly influence precursor decomposition and CNT deposition. CNTs were synthesised using aromatic and linear hydrocarbon precursors, including toluene and C6–C16 alkanes, at temperatures between 760 and 960 °C in an argon atmosphere. The results show that increasing alkane chain length enhances carbon availability and nanotube yield but reduces crystallinity and increases structural disorder, whereas moderate temperatures improve structural quality. Reactive MD simulations reveal that aromatic precursors promote stronger Fe–C interactions and stable iron cluster formation, favourable for ordered CNT formation, while longer alkanes generate intermediates that weaken catalyst clustering and increase structural heterogeneity. These findings suggest that differences in CNT structure originate already during the earliest stages of precursor decomposition, Fe clustering, and carbon-species evolution, prior to fully developed nanotube growth, and are governed not only by feedstock composition but also by reactor-scale effects.</jats:p>