Activity–Stability Relationships of Al ₂ O ₃ -Supported Ni Bimetallic Catalysts: Insights into Carbon Speciation for Dry Reforming of Methane

Catalysts used in dry reforming of methane (DRM) inevitably suffer from carbon deposition, but the nature and type of carbon deposited can be a determining factor in designing active and stable catalysts. Herein, we report a systematic analysis of Ni-based bimetal catalysts (Ni 3 Fe, Ni 3 Co, and Ni 3 Cu) that integrates DRIFTS, TGA, and Raman spectroscopy with DFT to elucidate the mechanisms governing carbon speciation. Experimental findings identify Ni 3 Fe and Ni 3 Co as effective catalysts, exhibiting controlled reversible deactivation (deactivation constant, k d ≈ 0.15–0.19 h –1 ), characterized by moderate deposition (≈6.10–6.60%) of readily oxidizable, mixed amorphous-graphitic carbon ( I D / I G ≈ 1). Contrarily, Ni 3 Cu suffered severe deactivation (deactivation constant, k d = 0.53 h –1 ), driven mainly by the accumulation of 25% amorphous carbon, as identified by TGA. DFT calculations rationalize these divergences by mapping distinct carbon formation and removal pathways on the preferred segregation state of each catalyst. Ni 3 Fe facilitates self-cleaning through direct oxidation (C → CO), while Ni 3 Co energetically favors the associative formyl pathway (CH → CHO), effectively bypassing the deep dehydrogenation that leads to carbon formation. Conversely, Ni 3 Cu imposes a prohibitive kinetic and thermodynamic barrier to both reactant activation and carbon gasification. These findings demonstrate that catalyst resilience is not merely defined by carbon suppression but by the selective stabilization of deposited carbon in its active, transient phase, primed for subsequent transformations.