Transformation of primary siderite during coal catalytic pyrolysis and its effects on the growth of carbon nanotubes

Although the synthesis of carbon nanotubes from coal can efficiently reduce the cost of preparing these materials, the effect of the primary minerals present in coal (e.g., Fe-containing siderite) on the growth of these structures has not been studied in depth. In this study, we used a bituminous coal containing siderite and investigated the changes of the original siderite phase and the growth mechanism of carbon nanotubes during a KOH-catalyzed coal pyrolysis process. The results shown that the primary Fe minerals played an important role in the formation of carbon nanotubes during coal pyrolysis. During the KOH-catalyzed pyrolysis of coal, the Fe present in the raw material migrated from the bulk to the surface of the coal particles, and enriched in some areas of the surface of the coal particle. KOH-catalyzed coal pyrolysis had a significant effect on the formation of micropores and the increase of specific surface area and pore volume in coal. The primary siderite in coal and the catalytic growth of carbon nanotubes, in line with the following mechanism: FeCO3 -> alpha-Fe -> Fe3C + Graphite -> carbon nanotubes. This study can provide new ideas for the utilization of low-rank coal resources rich in Fe mineral components.