Balancing Oxidation and Reforming Pathways for Energy-Efficient Methane Tri-Reforming over Ni/CeO₂

Methane tri-reforming (TRM) represents a promising pathway for simultaneous greenhouse gas utilization and syngas generation while improving the thermal efficiency of reforming processes. In this work, a 10 wt.% Ni/CeO₂ catalyst synthesized via a hybrid wet impregnation–solution combustion synthesis method was investigated for oxygen-assisted methane reforming under CH₄/CO₂/O₂ feed mixtures, without externally supplied steam. The reaction environment was systematically adjusted from partial oxidation (POX)-rich to dry reforming of methane (DRM)-rich conditions, including conditions close to the theoretical autothermal regime, to examine the transition between exothermic and endothermic pathways and their influence on catalytic behavior, syngas composition, and reactor energy demand. The catalyst demonstrated strong activity across all investigated feed compositions, with methane conversion exceeding 95% under oxygen-containing conditions at elevated temperatures (>700 °C). Feed composition strongly dictated syngas characteristics: POX-dominated mixtures generated H₂-rich syngas (H₂/CO up to ~1.7), DRM-rich conditions approached ratios near unity, and intermediate feeds near the autothermal regime provided balanced compositions (H₂/CO ~1.3–1.4) tailored for downstream synthesis. Continuous monitoring of reactor power consumption revealed a substantial reduction in external heating requirements under oxygen-assisted conditions due to internal heat generation, contrasting sharply with the high energy input demanded by endothermic DRM operation. Furthermore, post-reaction structural characterization (FESEM, TEM, and CHN) following 24 h on stream revealed that oxygen-containing feeds effectively suppressed carbon accumulation and preserved catalyst morphology. This was attributed to the strong metal–support interactions and high oxygen mobility of the CeO₂ support, which minimized coke deposition and Ni particle sintering. In contrast, DRM conditions promoted severe filamentous carbon formation (~23.73 wt.%) and particle growth. These results demonstrate that controlling the balance between oxidation and reforming pathways offers an effective strategy for thermally integrated, energy-efficient, and durable syngas production.