The thermocatalytic decomposition of methane is a promising method for hydrogen production. To determine the cause of carbonaceous catalyst deactivation and to produce high-value carbon, methane decomposition behavior and deactivated catalysts were analyzed. The surface properties and crystallinity of a commercial activated carbon material, MSP20, used as a methane decomposition catalyst, varied with the reaction time at a reaction temperature of 900 °C. During the initial reaction, MSP20 provided a methane conversion of ≥ 50%; however, the catalyst exhibited rapid deactivation as crystalline carbon grew at surface defects; after 15 min of reaction, approximately 33% methane conversion was maintained. With increasing reaction time, the specific surface area of the catalyst decreased, whereas crystallinity increased. The R-square value of the conversion–crystallinity relationship was significantly higher than that of the conversion–specific surface area relationship; however, neither profile was linear. The activity of the activated carbon catalyst for methane decomposition is mainly determined by the complex actions of the specific surface area and defect sites. The activity was maintained after an initial sharp decline caused by the continuous growth of crystalline carbon product. This study presents the application of carbonaceous catalysts for the decomposition reaction of methane to form COx- free hydrogen, while simultaneously yielding porous carbon materials with an improved electrical conductivity.

Mechanism of activated carbon-catalyzed methane decomposition process for the production of hydrogen and high-value carbon
    Abstract
    1 Introduction
    2 Materials and methods
        2.1 Methane decomposition process
        2.2 Analysis of methane decomposition
        2.3 Characterization
    3 Results and discussion
        3.1 Activated carbon-based methane decomposition characteristics
        3.2 Physical changes of catalyst after methane decomposition
        3.3 Pore characteristics of the carbon catalyst after the deposition of carbon products
        3.4 Electrical conductivity of catalysts after methane decomposition
        3.5 Effect of surface oxygen functional groups of catalysts on catalyst activity
        3.6 Crystallinity change of the catalyst due to methane decomposition
        3.7 Discussion
            3.7.1 Correlation between catalyst-specific surface area and methane conversion
            3.7.2 Correlation between the crystallinity of catalyst and methane conversion
            3.7.3 Summary of causes on catalyst deactivation
    4 Conclusion
    Anchor 20
    Acknowledgements 
    References

• Ji Su Yun(C1 Gas & Carbon Convergent Research Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon 34114, Republic of Korea, Department of Chemical Engineering and Applied Chemistry, Chungnam National University, Daejeon 34134, Republic of Korea)
• Ji Hong Kim(C1 Gas & Carbon Convergent Research Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon 34114, Republic of Korea)
• Seok Chang Kang(C1 Gas & Carbon Convergent Research Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon 34114, Republic of Korea)
• Ji Sun Im(C1 Gas & Carbon Convergent Research Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon 34114, Republic of Korea, Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon 34113, Republic of Korea)