Electronic structure of bimetallic CoRu catalysts modulates the early stages of SWCNT nucleation

Abstract

Nucleation of single-walled carbon nanotubes (SWCNTs) via chemical vapour deposition (CVD) of methane on CoRu bimetallic nanoparticles is simulated using quantum chemical molecular dynamics. By varying the Ru loading in the catalyst, we show the role of Ru in decreasing catalytic efficiency; C–H bond activation is impeded, key reactive intermediate species become longer-lived on the catalyst surface, and longer carbon chains are stabilised through the earliest stages of SWCNT nucleation. Analysis of the CoRu nanoparticle structure during the CVD process shows that this influence of Ru is indirect, with the catalyst adopting Ru–Co core–shell or segregated structures throughout nucleation, while Co exclusively drives the catalytic decomposition of the methane precursor. We show that the influence of Ru occurs via the electronic structure of the catalyst itself, by lowering the Fermi level of the catalyst due to lower energy 4d/5s states, in a manner consistent with d-band theory.