Graphene and carbon nanotubes by CH4 decomposition over Co-Al catalysts

Catalysts containing Co and Al were prepared to obtain graphene and carbon nanotubes (CNTs) via the catalytic decomposition of CH4. The catalysts were prepared by co-precipitation with molar percentages of Co between 50 and 100%. The effects on the formed carbon of the catalyst composition, reaction temperatures of 500-900 degrees C, and activation with hydrogen were evaluated. The carbon that formed during the reactions was analyzed using Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and temperature-programmed oxidation (TPO). The Raman spectra of the samples containing Al were characteristic of CNTs, with the I-G/I-D ratio increasing as the Co/Al ratio and reaction temperature increased. The Co100 sample presented a Raman spectrum indicative of few-layer graphene. The TPO analysis revealed cobalt carbide oxidation for the Co100 sample, and this phase was related to the formation of graphene. CNTs were favored by Co-Al mixed oxides and reaction temperatures of 500-700 degrees C. Graphene was favored by the Co3O4 phase and higher reaction temperatures.