Understanding metal-support interaction for single-walled carbon nanotube synthesis: a comparative study of Co on MgO and Al2O3

Abstract

As the demand for precisely tailored carbon nanotube (CNT) properties increases, catalyst design becomes increasingly important. In the field of catalysis, metal–support interaction (MSI) has been recognized as a key strategy for tuning catalyst performance. To better understand how MSI affects CNT synthesis, this study investigates cobalt-based catalysts supported on Al2O3 and MgO. CNTs synthesized using the Co/MgO exhibited higher crystallinity and broader diameter distribution than those synthesized using Co/Al2O3. Detailed characterization—including X-ray analyses, transmission electron microscopy, and temperature-programmed reduction—revealed that both catalysts exhibited MSI accompanied by compositional reconstruction, but through different mechanisms: Co/Al2O3 formed compounds, while Co/MgO developed solid solutions. Based on these findings, we proposed distinct mechanisms of metal nanoparticle formation to explain the different interphase formation behavior observed in the two catalyst systems. Utilizing this hypothesis, formation of solid solution in the Co/MgO catalyst was regulated by adjusting the calcination temperature, and enhanced solid solution formation promoted preferential growth of single-walled CNTs (SWCNTs) under specific conditions. Under these optimized Co/MgO conditions, the CNT product achieved ∼10% carbon yield, an IG/ID ratio of 4.5 ± 1.1, a TGA decomposition peak at 531.87 °C indicating high thermal stability, and facile purification leaving only 1.5% residual mass. Overall, this work highlights how different types of MSI—compound formation versus solid solution formation—can lead to fundamentally distinct CNT growth behaviors, providing new insights for the rational design of catalysts for SWCNT production.