Formation of filamentous carbon during methane decomposition over Co-MgO catalysts

The carbon formation during methane decomposition was investigated at 900 degreesC over the 48 wt% Co-MgO catalysts as a function of the calcination temperature T-c used in their preparation. Examination of the carbonaceous deposits by transmission electron microscopy revealed three kinds of structures: shapeless tangles, shell-like materials, and carbon filaments. In another set of experiments, the structural characteristics of the calcined catalysts were investigated using temperature-programmed reduction (TPR) and X-ray diffraction (XRD). Co3O4, Co2MgO4, and (Co, Mg)O (solid solution of CoO and MgO) were identified for T-c less than or equal to 700 degreesC, Co3O4 and (Co, Mg)O for T-c = 800 degreesC and only (Co, Mg)O for T-c = 900 degreesC. It was found that the metal particles originated from the reduction of the solid solution favored the formation of filamentous carbon. A possible explanation is proposed. (C) 2002 Elsevier Science Ltd. All rights reserved.