Synthesis of carbon nanofibers: effects of Ni crystal size during methane decomposition

Catalytic decomposition of methane over supported Ni catalysts with different particle sizes

“…These results agree well with Snoeck [13] and Kepinski's [16] observation that for catalyst particles greater than 20 nm, the growth rate of CNFs increases with decreasing catalyst particle size. However, as reported by Chen, [17] when the catalyst particles are smaller, the growth rate will decrease with decreased particle size, which was accounted for by the larger saturation concentration of CNFs and smaller driving force of carbon diffusion in smaller particles. Figure 3.…”

“…[20] The mechanism, which has generally been accepted, includes methane adsorption on the surface of Ni, conversion of the adsorbed methane into adsorbed surface carbon via surface reactions, subsequent segregation of surface carbon into the layers near the surface, diffusion of carbon through Ni, and then precipitation on the rare side of the Ni particle. [17] Among all the steps, diffusion of carbon through Ni is believed the rate determining step and can be expressed by the following equation: [21] …”

“…From this point, the Ni with small size should have higher CNFs growth rate. On the other hand, just as Chen [17] discussed, catalysts with small crystal size will result in a large saturation concentration of CNFs, leading to a low driving force of carbon diffusion and a lower growth rate. Based on the viewpoint described above, there must be an optimum particle size which leads to a maximum carbon yield.…”

Effect of Active Metal Supported on SiO2 for Selective Hydrogen Production from the Glycerol Steam Reforming Reaction

“…The reason for such behavior should be attributed to the mechanism of coke formation over Ni (Christensen et al 2006;Gonzalez-Dela Cruz et al 2008;Centi and Perathoner 2009). As a matter of fact, the growth of carbon nanofibers in such cases involves methane adsorption on the surface and its conversion into adsorbed carbon (Chen et al 2005). Then, carbon segregates into the layers near the surface by diffusion through Ni and precipitation on the rear side of the Ni crystal.…”

Effect of hydrogen on the synthesis of carbon nanofibers by CO disproportionation on ultrafine Fe3O4

“…It is also reported that H 2 will change the size of catalyst particles, [11] and smaller the particle size, the faster the catalyst deactivation. [14] Therefore, one can assume that the size of the fragmented catalyst particles is related to the fragment rate. Increasing H 2 concentration will increase the fragment rate of catalyst particle and produce smaller fragmented particles, which have a shorter induction period but a faster deactivation rate.…”