The role of molybdenum in Co-Mo/MgO for large-scale production of high quality carbon nanotubes

Abstract

The molybdenum (Mo) content in the bimetallic Co-Mo/MgO catalysts was observed to affect the carbon yield, diameter uniformity and quality of carbon nanotubes (CNTs) produced by the catalytic chemical vapor deposition (CCVD) of methane. The results show that a small amount of Mo added into the catalysts helps the dispersion of active metals on the surface of catalyst support and prevention of the agglomeration of active metal particles through the formation of thermally stable Mo species. The CNTs produced on the Co-Mo/MgO catalyst with different Mo contents, i.e. 5, 10, 20, 30, and 40 wt%, had the diameters of 8.25 ± 1.38, 7.96 ± 0.93, 7.16 ± 0.63, 8.62 ± 1.43, and 9.32 ± 1.66 nm, respectively. High concentration of Mo in the catalyst was suspected to result in the formation of lower graphitized graphene wall and lower the yield of CNTs due to the formation of MgMoO 4 and/or CoMoO 4 phases as deduced from the X-ray diffraction pattern and the thermogravimetric analysis. The optimum composition of Co-Mo/MgO catalysts was Co 5Mo 20MgO 75 as the catalysts with this composition produced the highest yield of CNTs (354.3%) with a little trade-off as shown in the thermogravimetric analysis.