Promoting Effect of Ruthenium on Fe-Catalyzed Growth of Small-Diameter Single-Wall Carbon Nanotubes

The role of Ru promotion of Fe catalysts in the growth of small-diameter single-wall carbon nanotubes (SWCNTs) has been investigated using an Autonomous Research System (ARES)a high throughput, laser-induced chemical vapor deposition (CVD) system capable of in situ Raman spectroscopy. Growth experiments in the ARES were conducted using a standard feedstock (ethylene) at 800 °C for Fe-Ru and Fe catalysts. The results show that Fe-Ru (with a composition ∼10%) supports the growth of small-diameter SWCNTs (less than 1.1 nm) compared to pure Fe. In addition, density functional theory (DFT) calculations on Fe nanoparticle clusters of 55 and 59 atoms with and without adding Ru were performed to probe the effect of Ru on the catalyst stability. The DFT results show that, irrespective of the exact distribution of Ru atoms within these clusters, the addition of Ru to Fe clusters increases the cohesive energy of the catalyst particle with respect to the pure Fe cluster. The combined Raman and DFT data indicate that high-melting-point transition metals can stabilize the catalyst nanoparticles and suppress sintering, thus increasing small-diameter selectivity of SWCNTs. This finding has been verified in a conventional hot-wall CVD system that utilizes industrial gaseous waste as a feedstock using multiexcitation Raman spectroscopy.