CH₄ Decomposition on Nickel Phyllosilicate: Switching from Tip to Base Growth of Carbon Nanotubes

The emerging trends in carbon nanotube applications make them exceptional functional materials of highly added value. Thermocatalytic CH₄ decomposition is an effective pathway toward their production, forming H₂ as the only byproduct. However, catalyst deactivation due to sintering and blockage of the active sites, together with their detachment from the support remains a challenge. In this work, nickel phyllosilicate is employed as a catalyst precursor for the formation of active and stable metal sites. Surprisingly, the particles remain attached to the support, switching from the typical tip-growth reported for state-of-the-art catalysts to a base growth mechanism. The nickel nanoparticles remain stable against sintering even under harsh conditions up to 750 °C. A combination of DFT calculations, in situ TEM, and in situ XRD studies reveals that the reduction of Ni─O bonds, particularly those involving silicon-bonded oxygen (Si─O─Ni; apical oxygen), requires high temperatures. Post-activation, the small, dispersed nickel nanoparticles catalyze CH₄ decomposition into carbon nanotubes and H₂. Unlike prior reports, in situ XRD confirms no nickel carbide formation in the bulk. Additionally, in contrast to any known nickel-based catalyst, it is demonstrated that particles below 10 nm can effectively activate CH₄ cracking, avoid encapsulation, and enable the base-growth of micrometer-long, narrow carbon nanotubes.