Mechanism of Catalytic CNTs Growth in 400–650 °C Range: Explaining Volcano Shape Arrhenius Plot and Catalytic Synergism Using both Pt (or Pd) and Ni, Co or Fe

摘要: The Arrhenius plot of catalytic carbon formation from olefins on Ni, Co, and Fe has a volcano shape in the range 400–550 °C with reaction orders 0 (at lower T: Below ~500 °C) one higher Above at each side maximum rate. follows route surface decomposition gas (olefin) catalyst nanoparticle, followed by bulk diffusion atoms nanotube growth opposite side. At temperature region (500–550 °C), initial step controls rate order is one, both hydrogen (H). This confirms that H essential for to occur. very valuable information get faster CNT relatively low temperatures. apparent activation energy observed must correspond Ea corrected dependence two molecules involved (olefin H). Adding noble metal (Pt, Pd) frequently found increase further. effect been described as an spillover since 1964. However, there evidence prevails does not “spillover” diffusion. Diffusion through solids easy, remain single (“independent”) until emerging surface.