Structural evolution and coke deposition-driven deactivation mechanism of industrial-scale steam methane reforming catalysts

Carbon deposition remains the most critical factor limiting the long-term stability of nickel-based catalysts in industrial steam methane reforming (SMR) for hydrogen production. To elucidate the mechanisms of large-scale catalyst degradation, an SMR unit with a capacity of 120,000 Nm 3 /h was systematically investigated by integrating industrial operation data with post-shutdown structural characterization. The analyses revealed a dual-mode coking mechanism driven by spatially distinct reaction environments: graphitic carbon formed in the pre-reformer through C2+ hydrocarbon pyrolysis at 400–500 °C, while amorphous carbon dominated in the main reformer due to methane decomposition and CO disproportionation under high-temperature, steam-deficient conditions. The latter led to a self-accelerating degradation process involving Ni particle sintering, potassium loss, catalyst fragmentation, and progressive pressure drop. This work systematically elucidated the deactivation mechanisms of Ni-based catalysts in an industrial-scale SMR reactor and established a clear relationship between coke morphology and structural failure. The findings provide practical insights for catalyst zoning, promoter stabilization, and startup optimization to improve the durability and safety of large-scale hydrogen reforming systems. • An industrial-scale study linking Ni catalyst deactivation with SMR plant. • Revealed stage-specific coke deposition and catalyst deactivation mechanisms. • Amorphous coke drives a self-reinforcing loop of Ni sintering and fragmentation. • Coke morphology is correlated with industrial symptoms. • Practical strategies proposed including anti-coking design and startup control.