Kinetic and Raman spectroscopic study on catalytic characteristics of carbon blacks in methane decomposition

Carbon blacks have been known to exhibit catalytic activities in methane decomposition. However, there remain problems in determining the activation energy and the time-varying catalytic characteristics. In the present study, the significance of carbon deposition on carbon black in a kinetic study was investigated, and the applicability of Raman spectroscopy to the characterization of carbon blacks was examined. First, the activation energy of carbon black was determined at two temperature ranges without taking into account the effect of carbon deposition, and the significant difference between them was observed. Then, the amount of deposited carbon was introduced in a kinetic study to represent the degree of change in catalyst properties due to carbon deposition. On the basis of the observation that the time-varying catalytic characteristics had clear correlations with the amount of deposited carbon, the evaluation method of the activation energy in which the effect of carbon deposition is taken into account was presented. The constant activation energy for each carbon black was obtained in the wide range of the amount of deposited carbon. The presented method was demonstrated to be useful in determining activation energies of carbon blacks which exhibit the time-varying catalytic characteristics. Finally, Raman spectroscopy was applied to carbon blacks, which included fresh ones and those used in the methane decomposition experiment for specified reaction times. The obtained Raman spectra exhibited significant changes in the initial deactivation stage. It was demonstrated that Raman spectroscopy was useful to characterize the initial structural evolution of carbon blacks.

► Significance of carbon deposition in a kinetic study was demonstrated.
► A new evaluation method of activation energies was presented.
► Activation energy invariant in all stages of time-varying behavior was obtained.
► Raman spectroscopy was applied to carbon blacks used in the reaction.
► Initial structural evolution of carbon blacks was successfully characterized.