Substrate-support interactions in metal-catalyzed carbon nanofiber growth

Catalyst-support interactions are critical in CVD processes for nanotube synthesis. In this article, the relative contributions of the catalyst electronic structure and support chemical composition are evaluated with Cu, Fe and Ni as catalysts and Al₂O₃, CaO, SiO₂ and TiO₂ as support media. The impact of the interaction is judged qualitatively based on nanotube growth and structure. Results are interpreted in terms of electron charge donation to the metal nanoparticle enabled by either strong-metal support interaction (SMSI) or by interaction of the catalyst nanoparticle with exposed Lewis base sites on the support material. The role of the physical structure of the support medium is explored by comparison of nanotubes grown upon powdered and fumed phases of the support oxides. Carbon nanotubes catalyzed by metal nanoparticles generated in-situ or preformed illustrate the advantage of presynthesized particles for size uniformity with attendant greatly lessened dependence upon catalyst preparation conditions. Catalyst retention and dispersion under rapid heating conditions is evaluated for the same support-catalyst systems listed above as a preliminary test for flame synthesis. Results show that SMSI interaction is critical to using the supported catalyst method in a flame.