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In situ and ex situ time resolved study of multi-component Fe[BOND]Co oxide catalyst activation during MWNT synthesis



Comparative in situ X-ray diffraction (XRD) study of activation Fe, Co, and Fe[BOND]Co catalysts on different supports (Al2O3 and CaCO3) for multi-walled carbon nanotube (MWNT) growth combined with ex situ high-resolution transmission electron microscopy (HRTEM) characterization has been performed. The catalyst contained Fe as an active component (mono-component Fe catalyst) demonstrates the simultaneous formation of Fe[BOND]C alloys (austenite and tetragonal ferrite like structure) with their subsequent transformation into stable iron carbide Fe3C (cohenite). The active component of bimetal Fe[BOND]Co catalysts (Fe:Co = 2:1) is Fe[BOND]Co alloyed nanoparticles, which does not demonstrate carbide formation. The absence of carbides promotes carbon diffusion through metal particle providing much higher activity of bimetal Fe[BOND]Co catalyst in comparison with the mono-component Fe and Co catalysts. Tubes produced using the bimetal catalysts have a high degree of structural perfection and narrow diameter distribution. The most active metal catalyst particles formed under reaction conditions are solid or at least have crystalline core. Pechini-type method used for Fe[BOND]Co catalyst production provides much higher MWNT yields than it was described elsewhere.

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Structure of active metal particles was proposed according to XRD data during MWNT growth on different type of catalysts with mono- and bimetal active component.