Spherical Structures Composed of Multiwalled Carbon Nanotubes: Formation Mechanism and Catalytic Performance

powder are presented by filtration steps in the slurry-phase operations and the large drops in pressure in fixed-bed reactors. These problems very much limit the application of CNTs on a large scale. The fabrication of carbon filaments on a structured support (e.g., activated carbon, carbon fibers, porous frameworks, graphite) [5, 6] has also suffered from discontinuities in the structure. The future use of CNTs has also been restricted by the technical requirements and the necessary high energy consumption of the complicated CVD process. To avoid mechanical post-treatment of CNT powder and the risk of explosion during CVD synthesis, we have explored a simple method to produce monolithic CNTs directly as millimeter-scale spheres, featuring an integral continuity in the structure from the microscopic to the macroscopic scale. The whole process of CNT growth has been conducted in a flow of ultrapure N2, involving a set of elementary steps in the solid phase which are less complex than the widely used CVD process. The growth of CNTs is based on a solid-phase reaction and well-graphitized nanotubes can be obtained even at temperatures as low as 4008C. All growth events were observed directly by in situ transmission electron microscopy (TEM), X-ray diffraction (XRD), IR and Raman spectroscopy, and thermogravimetric analysis. A commercial styrene–divinylbenzene copolymer resin