CoFe₂/CaO catalysts for multi-walled carbon nanotubes (MWCNT) were characterized during the activation period (T = 670 °C; C₂H₄/Ar = 1:1, 400 sccm) by internal field ⁵⁹Co nuclear magnetic resonance. During this induction period, although C₂H₄ is already reacting, the MWCNT yield remains negligible. The NMR spectra of the catalysts revealed the occurrence of several structural and magnetic species. They were not detectable by conventional X-ray diffraction but the heterogeneity of the metal particles was corroborated by high-resolution transmission electronic microscopy coupled with energy dispersive X-ray spectroscopy. Two samples quenched at different activation time contained, beside non-reacted pure metal Co particles, strong and weak ferromagnetic alloys. During activation, the pure Co metal content dropped and an increase of the ordering of the cobalt-iron alloy in the catalyst was evidenced thus revealing a multistage activation mechanism for the reaction. We propose this ordering process during the induction period to be an intermediate step between the strong ferromagnetic Co rich alloy and the weak ferromagnetic Fe rich one and that it favors the onset of MWCNTs growth.

通过内场⁵⁹ Co核磁共振对活化期（T = 670°C； C ₂ H ₄ / Ar = 1：1，400 sccm）表征了用于多壁碳纳米管（MWCNT）的CoFe ₂ / CaO催化剂。在诱导期，尽管C ₂ H ₄在已经发生反应的情况下，MWCNT的收率仍然可以忽略不计。催化剂的NMR光谱揭示了几种结构和磁性物质的出现。它们不能通过常规的X射线衍射检测到，但是通过高分辨率透射电子显微镜和能量色散X射线光谱法证实了金属颗粒的异质性。除了未反应的纯金属Co颗粒，强磁和弱铁磁合金外，还包含两个在不同活化时间淬火的样品。在活化过程中，纯净的钴金属含量下降，催化剂中钴铁合金的有序化得到了证实，从而揭示了反应的多级活化机理。