Methane Pyrolysisover Ordered Mesoporous Carbonsand Carbon Blacks: Catalyst Design and Impact of Carbon Deposition

Thermocatalytic decomposition of methane (TCDM) is a promising technology that can produce low-cost, low-emission hydrogen (H₂) by the decomposition of methane into H₂ and value-added solid carbon. Catalyst deactivation concerns caused by coking, particularly prevalent in metal-based catalysts, can be alleviated using a carbon catalyst. Innovative ordered mesoporous carbons (CMK8, CMK9, and SMC2) have been synthesized via templating techniques and benchmarked for methane pyrolysis alongside various commercially available carbon blacks in a fixed-bed reactor to improve the catalytic performance. SMC2 combined a large specific surface area (SSA) of 1234.3 m² g_cat,o^–1 and pore volume of 2.6 cm³ g_cat,o^–1. The impact of carbon depositions on catalytic performance has been analyzed by assessing activity-property relations of fresh and spent catalysts, supported by N₂-physisorption, X-ray photoelectron spectroscopy, Raman spectroscopy, bright-field scanning transmission electron microscopy (BF-STEM) imaging, and CHN/O analysis. SMC2 showed a higher initial space-time yield (62 μmol H₂ g_cat,o^–1 s^–1) and H₂ selectivity (97%) than carbon black pearls 2000 and sustained activity (30 μmol H₂ g_cat,o^–1 s^–1) for 3 h. After 180 min of reaction, the carbon yield reached 2.31 g_carbon g_cat,o^–1. The high initial activity was attributed to a large external SSA, high oxygen content, low micro- to mesoporous surface ratio, surface defects, and a high fraction of graphene edge carbons. Pronounced stability is found for materials with a large final SSA and pore volume, allowing carbon to be deposited over a longer period. This work enables descriptor-based catalyst optimization to enhance the initial space-time yield and long-term stability of carbon catalysts for TCDM, advancing their suitability for industrial-scale H₂ production.