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

Abstract

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), N₂ physisorption (BET), H₂ temperature-programmed reduction (H₂-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.