Towards a Mechanistic Understanding of the Floating Catalyst CVD of CNTs: Interplay Between Catalyst Particle Nucleation, Growth and Deactivation

The chemical vapor deposition (CVD) of carbon nanotubes (CNTs) with the floating catalyst technique, using ferrocene as catalyst, is computationally investigated from its mechanistic perspective. The present work presents a novel model dealing with the phenomena taking place in the bulk of a floating catalyst CVD reactor. The developed model incorporates the gas flow, heat transfer and species transport phenomena, coupled with reaction mechanisms and kinetics, as well as the catalyst particle formation and growth dynamics. The novelty of the approach lies on the inclusion of carbon species deposition on the catalyst particle surface, which have a crucial effect on the particle growth and catalyst deactivation, leading to the termination of CNT growth on the particles. The model predictions are directly compared with experimental results from the literature for the same process and for a range of process parameters, showing a very good agreement. The computational model not only successfully predicts the experimental behavior but also reveals the effect of individual mechanisms on the inhibition of particle growth, catalyst deactivation and CNT growth. In this way, the model provides an in-depth mechanistic understanding of the mechanisms in the reactor bulk, which is currently missing, thus paving the way towards the knowledge-based process design and optimization and the possibility of using more sustainable or environmentally-friendly precursors and catalysts which have not been studied experimentally in detail.