(544fj) Methane Decomposition for Carbon Nanotubes and COx-Free H2 over Fe-Based Catalysts on Different Supports

I-Wen Wang, Deepa Ayillath Kutteri, Bingying Gao, Hanjing Tian, and Jianli Hu*

Department of Chemical and Biomedical Engineering, West Virginia University, Morgantown, WV 26506

Recently, our group reported a promising catalyst innovation for non-oxidative thermochemical conversion of methane to CO_x-free hydrogen and multi-walled carbon nanotubes (CNT’s). A catalyst system was discovered that produced more “base growth” CNT formation than conventional “tip growth”. This enables catalyst regenerability while also generating highly pure and crystalline carbon product. In this study, two productions of CNT’s and CO_x-free hydrogen were studied over Fe-based catalysts supported on Al₂O₃, SiO₂, and ZSM-5. The conversion of methane and the property of CNT’s depended significantly to the different supports and the metal loadings. The results revealed that metal-support interaction played a key role in base-growth mechanism. To study the properties of CNT, the spent catalysts were characterized by different analytical instruments including TEM, XPS, XRD, Raman, and TGA. The formation of active intermediate phase, Fe₃C, was discovered. The results of XPS analysis revealed that Fe over Al₂O₃ had a stronger interaction between metal particles and supports than SiO₂ and ZSM-5. The characterization result is consistent with the results that Fe/Al₂O₃ performed higher activity on the decomposition of methane. To further explore the application of the CNT, purification was carried out using spent Fe/Al₂O₃ and 9NiFe/SiO₂ catalysts. The spent catalysts with CNT’s were purified by refluxing in nitric acid to dissolve metal particles and supports. The purity of CNT recovered from the Fe/Al₂O₃ catalyst can reach high purity based on TGA analyses. Also, XRD and SEM-EDS analyses showed that most metal particles and Al₂O₃ supports had been dissolved. In addition, the purified CNT’s presented a good dispersion stability in isopropanol solution, implying the presence of functional groups on CNT that interacted with isopropanol solvent.