Catalytic partial oxidation of methane over NiO-MgO/Ce0.75 Zr02.25O2 catalysts: effects of low Mg content and its incorporates sequences

Abstract

The NiO/Ce0.75Zr0.25O2 (Ni/CZO) catalyst has been demonstrated to be highly active for synthesis gas production via catalytic partial oxidation of methane (CPOM), yet deactivation remains an unsolved impediment mainly due to carbon deposition and NiO sintering. Although magnesium (Mg), as a promoter, has been observed to suppress carbon deposition and agglomeration of NiO particles under high temperature conditions, resulting in improved stability of the catalyst, the addition of MgO onto the catalyst at higher amounts (>5 wt %) caused lower catalytic zctivity. In order to improve the catalytic activity, NiO-MgO/Ce0.75Zr0.25O2 catalysts with the Mg content of 1-6 wt% were prepared via the multi-step incipient wetness impregnation method. The amount of Ni loading was fixed at 15 wt% whereas Mg loading was varied. The metal incorporated sequences were carried out in such a way that Mg is incorporated onto the CZO followed by Ni incorporation or vice versa. The catalysts were characterized by BET, XRD, XRF, TPR, TPO, and SEM techniques. The catalysts were tested for catalytic activity on CPOM in the temperature range from 400 C to 800C at atmospheric pressure. The results revealed that an increase in Mg loading resulted in lowering both the catalytic activity and carbon deposition. Moreover, the incorporated sequence has a significant influence on reductibility, reactivity and stability of the catalysts. At a given amount of Mg loading higher 1 wt%, the NiO-MgO/CZO, Mg impregnated first, has demonstrated to be more active for CPOM than the MgO-NiO/CZO. However, the carbon deposition was observed to be more suppressed on the MgO-NiO/CZO as compared to the Ni/CZO catalyst.