Ni-Co/Al2O3 Bimetallic Catalysts for CH4 Steam Reforming: Elucidating the Role of Co for Improving Coke Resistance

A series of supported Ni-Co/gamma-Al2O3 bimetallic catalysts with a fixed 12% Ni loading but different Co contents were prepared by using the coimpregnation method and investigated for methane steam reforming. The addition of Co can significantly improve the coke resistance and the reaction stability of Ni/Al2O3 at a mild loss of the reforming activity. XPS and TEM results prove the existence of strong interaction between Ni and Co species. XRD and high-angle annular dark-field scanning transmission electron microscopy mapping results of the reduced catalysts provide direct evidence for surface Ni-Co alloy formation upon Co addition onto Ni/Al2O3, which can block part of the active low coordinated Ni sites and lower the metal dispersion, thus effectively suppressing coking and improving the reaction stability in comparison with the unmodified Ni/Al2O3 catalyst.