Elucidation of the Influence of Ni-Co Catalytic Properties on Dry Methane Reforming Performance

Abstract

Carbon deposition is a major problem of dry methane reforming (DMR) over Ni-based catalyst. Recently, Ni- Co bimetallic catalyst has shown the improvement of carbon resistance of Ni-based catalyst. The objective of this work is to study the influence of properties of Ni-Co catalysts on its DMR performance, as well as the influence of Ni-Co alloy formation in Ni-Co catalyst. In this work, Al-Mg mixed oxide (Al-Mg-O) was prepared by sol-gel method. Catalyst samples; 10 wt% Ni/Al-Mg-O (Ni/MA), 10 wt% Co/Al-Mg-O (Co/MA) and 5 wt% Ni- 5 wt% Co/Al-Mg-O (Ni-Co/MA), were prepared by incipient wetness impregnation method. All catalysts were characterized by H₂-TPR, H₂-TPD and TPH. The results indicate that Ni-Co/MA provides excellent reducibility with strong metal support interaction (SMSI) as compared with monometallic catalysts. The bimetallic catalyst also exhibits better metal dispersion. Ni-Co/MA shows highest performance of CO₂ adsorption. TPH profiles of spent catalysts from CH₄-decomposition and CO₂-decomposition reveal that Ni-Co/MA can suppress coking from both decomposition reactions, whereas TPH profiles of Ni/MA and Co/MA show the hydrogenation of carbon deposition from CH₄-decomposition and CO₂-decomposition. DMR tests over catalyst samples were carried out at 620 °C under atmospheric pressure with the flow of CH₄:CO₂:N₂ mixture after the reduction at 620 °C for 12 h. The H₂/CO ratio of DMR over Ni-Co/MA is 0.94 which is close to stoichiometry ratio (unity) without the occurrence of carbon deposition. This result can be attributed to the high CO₂ adsorption performance with excellent carbon resistance. The effect of Ni-Co alloy formation of Ni-Co/MA on DMR was investigated when Ni-Co/MA was reduced at higher temperature (800 °C). It was found that increasing in the degree of alloy formation between Ni-Co improves the selectivity of the catalyst which shows H₂/CO ratio of almost unity.