Self-Activation of Iron-Loaded Metallurgical Coke during Methane Pyrolysis and Upcycling of the Spent Catalyst for Steelmaking

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Abstract Methane catalytic pyrolysis for hydrogen production is hindered by rapid catalyst deactivation due to carbon deposition—a long-standing technical bottleneck. This study proposes and experimentally validates an alternative pathway that reinterprets catalyst deactivation not as failure, but as an in situ synthesis step for a high-value metallurgical composite feedstock, thereby enabling full upcycling of the spent catalyst. An iron-based catalyst supported on industrial metallurgical coke (Fe/Coke) exhibits self-activation behavior during methane pyrolysis. Under optimized conditions (900 °C and CH4 flow rate of 10 mL·min−1), methane conversion increases progressively with time, reaching 93% within 7 h and delivering a hydrogen yield of 9.94 mmol·gcat−1·h−1. Multi-scale characterization demonstrates that self-activation arises from reaction-induced structural evolution: α-Fe particles undergo carburization to Fe3C, concurrent particle refinement from several hundred nanometers to tens of nanometers, and in situ deposition and graphitization of carbon to form a Fe3C@C core−shell architecture with an open mesoporous structure. Kinetic analysis reveals a marked decrease in apparent activation energy, from 166.6 kJ·mol−1 initially to 36.5 kJ·mol−1 after 3 h of reaction. DFT calculations further confirm that the Fe3C surface lowers the C−H bond dissociation barrier to 0.594 eV, substantially below that of α-Fe (0.735 eV), through collective charge redistribution mediated by the Fe−C hybridization network. The resulting composite, Fe/Coke@C, exhibits enhanced CO2 gasification reactivity relative to industrial metallurgical coke, suggesting potential for reuse as a steelmaking feedstock. Preliminary techno-economic analysis indicates that, at a 10 kg H2·h−1 scale, the process achieves a net profit margin of approximately 25.8%, although this estimate is based on laboratory-scale data and requires further validation at a pilot scale. This study presents an approach that reinterprets catalyst deactivation as a potential resource integration step for concurrent green hydrogen production and sustainable metallurgical feedstock supply.

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