Effect of molybdenum carbide concentration on the Ni/ZrO2 catalysts for steam-CO2 bi-reforming of methane

The effect of the molybdenum carbide concentration, in the range of 0.2-3.0 wt% (nominal loading), on modified supported nickel catalysts on ZrO2 (Mo2C-Ni/ZrO2) for steam-CO2 bi-reforming of methane was investigated by correlating the various characterization results, including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), N-2 physisorption (BET), H-2 temperature-programmed reduction (H-2-TPR), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and thermogravimetric analysis (TGA), to the catalytic performance. It was found that the Ni dispersion increased with an increase in Mo2C loading, which might lead to the strong Ni-ZrO2 interactions confirmed by XPS. However, an appropriate Mo2C loading is required to obtain a high surface Mo(II) content that may promote the reforming reaction by serving as another active species besides Ni. The optimized modified Ni/ZrO2 with 0.5 wt% nominal Mo2C loading exhibits higher catalytic activity than the others for steam-CO2 bi-reforming of methane, which is ascribed to an increased Ni dispersion and a higher Mo(II) content. Moreover, the developed 0.5 wt% Mo2C-10 wt% Ni/ZrO2 catalyst shows higher catalytic stability in comparison with the unmodified 10 wt% Ni/ZrO2 catalyst, which is ascribed to the different coke types caused by the diverse strength of the Ni-ZrO2 interactions for the modified and unmodified catalysts.