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

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.