"Hijacking" small-sized grains during the dynamic transformation between crystalline and amorphous phases in Fe-Mo NPs to catalyze carbon nanotubes growth

Coalescence induced by the dynamic evolution of catalysts under catalytic environments has long been a challenge in the growth of carbon nanotubes (CNTs). Herein, this study reports a catalyst "hijacking" strategy, which leverages the time-dependent difference during the crystalline-to-amorphous transformation of catalysts to activate the catalytic activity of small-sized crystalline nanoparticles, preventing their coarsening via Ostwald ripening. Simultaneously, the retained nanoparticles exhibit higher density and optimized electronic structures, extending the catalytic lifetime. The successful synthesis of the catalyst relies on the efficient utilization of Mo in open cavities, where the isolated open cavities restrict excessive coalescence of the active components, and the doping of Mo atoms induces the transformation of the active components from amorphous to crystalline. In this structure, the semi-confined space, surface negative charge, and affinity to solvents facilitate the formation of small-sized NPs by isolating and dispersing metal ions. Meanwhile, Fe-Mo bonds significantly prolong the length of CNTs. The combination of Fe and Mo promotes gradual crystallization of NPs, suppresses excessive coalescence of the active components, and optimizes the adsorption energy of C 3 H 6 , thereby extending the catalyst lifetime. Additionally, the bonding between Mo and C atoms favors bulk diffusion of C within Fe NPs, avoiding excessive C deposition inside the NPs and enhancing structural stability. As a result, the CNTs grown with this catalyst exhibit a small tube diameter as low as 5.68 nm and a high ratio (M product /M catalyst ≈14), demonstrating promising application prospects. Download: Download high-res image (212KB) Download: Download full-size image