%0 Journal Article
%T Mechanism of Catalytic CNTs Growth in 400¨C650 ˇăC Range: Explaining Volcano Shape Arrhenius Plot and Catalytic Synergism Using both Pt (or Pd) and Ni, Co or Fe
%J C ˇŞ Journal of Carbon Research | An Open Access Journal from MDPI
%D 2019
%R https://doi.org/10.3390/c5030042
%X The Arrhenius plot of catalytic carbon formation from olefins on Ni, Co, and Fe has a volcano shape in the range 400¨C550 ˇăC with reaction orders 0 (at lower T: Below ~500 ˇăC) and one (at higher T: Above ~500 ˇăC) at each side of the maximum rate. The reaction follows a catalytic route with surface decomposition of the gas (olefin) on the catalyst nanoparticle, followed by the bulk diffusion of carbon atoms and carbon nanotube growth on the opposite side. At the higher temperature region (500¨C550 ˇăC), the initial surface reaction step controls the rate and the reaction order is one, both in olefins and hydrogen (H). This confirms that H is essential for the surface reaction to occur. This is very valuable information to get faster CNT growth rate at relatively low temperatures. The apparent activation energy observed must correspond with the surface reaction E a corrected for the temperature dependence of the two molecules involved (olefin and H). Adding a noble metal (Pt, Pd) to the carbon formation catalyst is frequently found to increase the reaction rate further. This effect has been described as an H spillover since 1964. However, there is evidence that the bulk diffusion of H atoms prevails and does not ˇ°spilloverˇ± the surface diffusion. Diffusion of H atoms through the solids involved is easy, and the H atoms remain single (ˇ°independentˇ±) until emerging on a surface. View Full-Tex
%U https://www.mdpi.com/2311-5629/5/3/42