Double-Layer Support Strategy for Enhancing the Lifetime of Fe Catalyst Nanoparticles in Synthesis of Single-Walled Carbon Nanotubes

Abstract

While the catalyst support layer enables the preparation of catalyst nanoparticles arrayed at high density, they are susceptible to instability in the catalyst activity lifetime due to surface and bulk diffusion mechanisms. This study proposes a strategy to mitigate this limitation by maintaining structural stability and thus chemical reactivity using a double-layer (DL) support architecture. In place of a single support layer, which cannot adequately perform two functions, i.e., inhibit subsurface diffusion and impede surface diffusion mechanisms, the DL support uses two distinct metal oxide layers to address each issue. The DL support is composed of a top "anchor layer" to impede surface diffusion mechanisms, such as Ostwald ripening, and a high crystallinity "sealing layer" to inhibit subsurface diffusion. Elucidation of the roles and requirements of each layer allowed for the generalization of this approach to alternative support material combinations. In this way, we demonstrated significant improvements in the stability and performance of the catalyst array. Furthermore, we demonstrated the growth of millimeter-tall single-walled carbon nanotube (SWNT) forests, suggesting the potential of DL supports for optimizing catalyst performance.