Investigations on the effects of CoOx to MoOx ratio and CoOx–MoOx loading on methane decomposition into carbon nanotubes

The effects of CoOx to MoOx ratio and loading amount of CoOx–MoOx for Al2O3 supported catalysts on methane decomposition into carbon nanotubes (CNTs) were investigated. The reaction was performed in a fixed-bed vertical reactor at 700 °C. It has been shown that a small amount of molybdenum added brought about considerable increases in carbon yield. The highest carbon yield was recorded for the catalyst CoOx:MoOx with weight ratio of 8:2. The examination of catalyst activity and carbon morphology reveals that an increase in the molybdenum content reduced the carbon yield and formed CNTs of smaller diameter and narrower diameter distribution. The study also shows that CoOx–MoOx loading determines the yield of carbon and the diameter of CNTs. The yield of carbon reached the maximum at 30 wt% loading, and subsequent increases in the loading amount decreased the yield. In addition, severe agglomeration of CoOx–MoOx alloy particles for high loaded CoOx–MoOx-containing catalysts led to the formation of larger alloy clusters that grew CNTs with comparatively larger diameters.