Impact of Co addition on the stability of Ni-based catalysts on delaminated smectite for biogas reforming

Abstract

Biogas is a renewable resource that can be converted into syngas via Ni-catalyzed dry reforming (DR) and serves as a precursor for e-fuel synthesis. However, the high CH₄ content in biogas accelerates Ni catalyst deactivation owing to carbon deposition. In this study, the effect of the Co addition (5 wt%) to a Ni catalyst (10 wt%) supported on delaminated mesoporous smectite for biogas DR was evaluated. Physicochemical characterization revealed that Co doping induces synergistic effects, including Ni-Co alloy formation that mitigates sintering, a decrease in metal particle size from 25.7 nm to 17.1 nm, increased basicity from 120 to 183 μmol·g_cat⁻¹, and enhanced reducibility from 90 % to 98 %. Catalytic tests were conducted at 700 °C and 25 L·g_cat⁻¹·h⁻¹ using a synthetic biogas mixture (CH₄/CO₂/N₂ = 45/35/20) without prior H₂ reduction. Co incorporation improved catalyst stability by reducing carbon accumulation, likely due to enhanced gasification. In contrast to the higher values observed for the Ni-only catalyst, the H₂/CO ratio for the Ni-Co catalyst remained in the range of 1–2. Additionally, no severe re-oxidation or sintering of the metallic phase was observed. The coke formed mainly consisted of low-crystallinity multi-walled carbon nanotubes, which were oxidized at lower temperatures for the Ni-Co catalyst. Regeneration by carbon combustion at 700 °C resulted in a maximum loss of 10 % in CH₄ conversion and 5 % in CO₂ conversion per cycle, with a 9.7 % increase in the carbon mass. These results highlight the potential of Ni-Co catalysts for stable biogas DR with improved regenerability.