Ni- and Cu-based catalysts for hydrogen production via steam reforming: Mechanisms, active structure evolution, and stability

Steam reforming is a major route for hydrogen production, yet coke formation, sintering, and interfacial degradation progressively destabilize catalysts. This review examines working state evolution and active-structure retention in Ni- and Cu-based catalysts as two mechanistically distinct steam-reforming regimes, focusing on how reaction-relevant active sites and interfaces evolve, deactivate, and are stabilized under operating conditions. Because the two catalyst classes differ substantially in feedstocks, reaction temperatures, and dominant mechanisms, the analysis emphasizes transferable stability principles rather than direct performance ranking. For high-temperature Ni catalysts, durable operation requires balancing C–H/C–C bond activation with steam-assisted removal of carbonaceous intermediates and suppression of particle migration. For lower-temperature Cu-catalyzed methanol reforming, stability depends on maintaining system-dependent Cu 0 /Cu + -oxide interfacial states while limiting sintering, valence drift, and adsorbate-induced reconstruction. Evidence from density functional theory (DFT), molecular dynamics (MD), and in situ/ex situ characterization is integrated to link structure, pathways, and deactivation. Machine learning (ML) is assessed separately for descriptor prioritization, catalyst screening, and stability prediction. Future studies should evaluate working-state retention under realistic steam-to-carbon ratios, impurities, space velocities, and extended time-on-stream to guide durable catalyst design for practical hydrogen production systems.