Abstract
Abstract CoMo/MgO catalysts with low loading of cobalt and molybdenum were prepared by incipient wetness impregnation and the sol-gel method for high yield production of carbon nanotubes (CNT). A detailed characterization of the catalysts, as-produced CNT and purified CNT, indicated a relationship between carbon nanotube properties, synthesis and purification steps. Excess of molybdenum in the catalyst caused a decrease in carbon yield and produced CNT with a lower degree of graphitization. Catalysts prepared by the sol-gel method and with higher molybdenum loading showed an improved interaction between cobalt and molybdenum, increasing the formation of CoMoO4, which was not completely removed during the purification step. The purification removed all MgO and part of the cobalt and molybdenum present in samples without significant damage to the CNT structure. An increase in sample purity could be achieved by increasing reaction time.
Highlights
The production of carbon nanotubes has become interesting due to their unique properties since first reported by Ijima (1991)
The EDX spectrometer used in the experiments is equipped with a beryllium window, so the detectors cannot detect X-rays from elements lighter than sodium, including carbon and oxygen X-rays
X-ray diffraction (XRD) and Temperature programmed reduction (TPR) results showed that the calcined catalysts have many cobalt, molybdenum and magnesium oxide species and some of them are reduced at the same temperature range, which made it difficult to identify and quantify these oxides
Summary
The production of carbon nanotubes has become interesting due to their unique properties since first reported by Ijima (1991). The values of surface area (SBET), pore volume (Vp) and the average pore diameter of catalysts (Dp) prepared by the impregnation method were slightly where mcarbon is the carbon weight loss during TGA analysis and mcatalyst is the weight of the catalyst after sample oxidation obtained at the end of the TGA. XRD and TPR results showed that the calcined catalysts have many cobalt, molybdenum and magnesium oxide species and some of them are reduced at the same temperature range, which made it difficult to identify and quantify these oxides.
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