| Summary: | 碩士 === 國立中興大學 === 環境工程學系所 === 106 === In this study, we used a novel core-shell catalyst to catalyze methane cracking reaction for the production of carbon nanotubes. We found that the carbon nanotubes with a controllable diameter can be produced by tuning the pore size of the shell. A novel and simple synthetic approach toward core–shell Fe@Al2O3 nanoparticles was developed in this study. Fe@Al2O3 nanostructures were formed by the immersion of Fe@C nanoparticles with Al precursor in deionized water. The as-synthesized core-shell catalyst was applied to convert the methane into carbon nanotubes. The structure property and morphological nature of the fresh and used catalysts were confirmed by different characterization analysis such as SEM, TEM, BET. Moreover, the purity and species of the nanocarbon materials were also identified by Raman spectroscopy and thermogravimetric analysis.
According to the experimental results, it was known that the core-shell catalyst affects the structural characteristics at different calcination temperatures and Al/Fe molar ratios. In the case of Al/Fe=1.5 mole ratio, there are relatively more γ-Fe2O3, which is favorable for catalytic formation of methane into carbon nanotubes. For the calcining temperature of 750 °C, the most appropriate core-shell bonding ability is provided to prevent the core-shell structure from being destroyed. In the case of CTAB/Al=1 mole ratio, the core- shell catalyst catalyzes the cracking of methane to produce 135.9 mgC/gcat./h of carbon, and the methane conversion is as high as 95%.
The pore size of the shell changed with the CTAB concentration, and further produced a carbon nanotube with a tunable diameter. From the analysis results, it was found that the average diameter is 19.24 nm at CTAB/Al=0; the average tube diameter is 28.59 nm at CTAB/Al=0.5; average tube diameter is 58.06 nm at CTAB/Al=1.
In addition, the catalytic performance of the core-shell catalyst in the methane cracking at different temperatures and reaction gas concentrations was investigated. It was found that the Fe@Al2O3 core-shell catalyst exhibits up to 90% of methane conversion under any reaction temperature (700 °C, 750 °C, 800 °C) and initial methane concentrations (3%, 5%, 10%). Compared with traditional supported catalysts, core-shell catalyst is more suitable for high-temperature environments. The methane conversion remains at 95% for nearly 3 hours under 800 ℃ reaction temperature. This work gives a vision towards the design and synthesis of advanced catalysts for chemical vapor deposition.
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