H2 production from methane decomposition by fullerene at low temperature

Carbon materials have previously been reported to work as catalysts for hydrogen (H₂) production from hydrocarbons. Mechanisms of the catalytic behavior of graphite and carbon black (CB) have often been discussed in literature. Graphite and CB is constructed from mainly 6-membered rings with sp² bonds. To understand the catalytic behavior of carbon materials for H₂ production by methane (CH₄) decomposition, the catalytic behavior of fullerenes with 6-membered rings and also those comprising 5- and 7-membered rings with sp² bonds and their associated mechanisms should be investigated. In this study, the fullerene catalyst activity has been investigated using gas chromatography and the electronic states and nanoscale structures have been analyzed.H₂ production started at 400 °C and the H₂ production rate gradually increased with time, and the activation energy of the fullerene for H₂ production by CH₄ decomposition was found to be 166 kJ/mol. Moreover, in situ heating X-ray photon spectroscopy (XPS) measurements showed that the π-π1 transition signal becomes stronger with increasing temperature above the threshold of 300 °C. The transition of the π electrons to π1 orbitals upon heating is expected to decompose CH₄ absorbed on fullerene. Moreover, transmission electron microscopy (TEM) analysis revealed that the generated carbon atoms from the CH₄ decomposition were deposited onto the surfaces of the fullerenes, forming amorphous and layered concentric sphere carbon. Amorphous carbon is reported to not work as a catalyst for CH₄ decomposition at around 400 °C. From XPS analysis and TEM observations of these two structures, it is anticipated that the ring structures without 6-membered rings in carbon materials with sp² bonding contribute to this catalytic behavior for CH₄ decomposition at a low temperature of 400 °C.