Kinetic study of carbon nanotube synthesis over Mo/Co/MgO catalysts

Abstract

The kinetics of carbon nanotube (CNT) synthesis by decomposition of CH 4 over Mo/Co/MgO and Co/MgO catalysts was studied to clarify the role of catalyst component. In the absence of the Mo component, Co/MgO catalysts are active in the synthesis of thick CNT (outer diameter of 7-27 nm) at lower reaction temperatures, 823-923 K, but no CNTs of thin outer diameter are produced. Co/MgO catalysts are significantly deactivated by carbon deposition at temperatures above 923 K. For Mo-including catalysts (Mo/Co/MgO), thin CNT (2-5 walls) formation starts at above 1000 K without deactivation. The significant effects of the addition of Mo are ascribed to the reduction in catalytic activity for dissociation of CH 4, as well as to the formation of Mo 2 C during CNT synthesis at high temperatures. On both Co/MgO and Mo/Co/MgO catalysts, the rate of CNT synthesis isproportional to the CH 4 pressure, indicating that the dissociation of CH 4 is the rate-determining step for a catalyst working without deactivation. The deactivation of catalysts by carbon deposition takes place kinetically when the formation rate of the graphene network is smaller than the carbon deposition rate by decomposition of CH 4 .

The Effect of Metal Loading on the Performance of Tri-metallic Supported Catalyst for Carbon Nanotubes Synthesis from Liquefied Petroleum Gas

“…. These five peaks attributed to MgO were also detected in the XRD pattern of the reduced Fe-Mo/MgO catalyst in a study conducted by Ni et al (2009) and in the XRD pattern for the calcined as well as reduced CoMo/MgO catalyst, also reported earlier by Ni et al (2006). The patterns also demonstrated that the intensity of the MgO peaks decreased as the metal loading increased.…”

Quantitative study of catalytic activity and catalytic deactivation of Fe–Co/Al2O3 catalysts for multi-walled carbon nanotube synthesis by the CCVD process

“…(4) corresponds to the following sequence of elementary steps, which consists of equilibrated adsorption of ethylene and of the irreversible surface ethylene decomposition as the ratedetermining step [34]: Activation energy E 2 was found to be equal to around 120 ± 15 kJ mol −1 , standard adsorption enthalpy H • to around −120 ± 20 kJ mol −1 , and standard adsorption entropy S • to around −120 ± 20 J mol −1 K −1 . As a comparison with previous literature, reported activation energies for ethylene decomposition into carbon nanotubes and hydrogen vary between 100 kJ mol −1 and 180 kJ mol −1 , depending on the catalyst nature [28,[34][35][36][37], while reported ethylene adsorption enthalpies with different catalyst vary from −160 kJ mol −1 to −60 kJ mol −1 [28,38,39]. Let us mention that ethylene adsorption enthalpy and entropy, H • and S • , must verify thermodynamic constraints.…”

Simulation and modeling of carbon nanotube synthesis: current trends and investigations

“…(2009) [9] Carbon nanotube synthesis by fluidized bed chemical vapor deposition [15] CNT synthesis by the CVD process…”

“…It was shown that the longest CNTs can be achieved in the temperature range of 825 -875 ° C. Increase in the concentration of both xylene and ferrocene resulted in an increase of the average height of CNTs. Ni et al [15] conducted a kinetic study of CNT synthesis over Mo/Co/MgO catalysts. Recently, Raji et al [16] developed a chemical kinetic model to describe the dependency of operating parameters on the deposition condition of growth of CNTs, which yielded results as shown in Figures 2E and 3E.…”