Dry reforming of methane with carbon dioxide over NiO–MgO–ZrO2

• Melt impregnation to obtain NiO–MgO–ZrO2 catalysts with 2–35 Ni and Mg.
• Ni and Mg are homogeneously distributed as oxides on the zirconia.
• Highly dispersed Ni0 and a NiO–MgO solid solution are present on the support.
• Coking includes growth of MWCNT and graphitic carbon, encapsulating Ni0 particles.

NiO–MgO–ZrO2 catalysts were synthesized via a melt impregnation technique on a zirconia support with equimolar amounts of Ni and Mg in the range of 2–35 mol%. The catalysts were characterized by TPDA, TPR, PXRD, TEM and EDX. The catalysts are basic in nature and contain both tetragonal and monoclinic zirconia. After impregnation, Ni and Mg are homogeneously distributed over the zirconia support in oxidic form. After reduction of the composite system, metallic Ni is highly dispersed on the support together with a solid solution of NiO–MgO present. The prepared NiO–MgO–ZrO2 catalysts show a high activity in the dry reforming of methane at 1123 K and atmospheric pressure. At high Ni and Mg contents, the catalysts are subject to severe coking leading to pronounced deactivation. From TEM investigations, a coking mechanism is proposed including the growth of filamentous carbon followed by formation of graphitic carbon, partly encapsulating metallic Ni particles. An optimum stability can be achieved in a small compositional corridor with Ni and Mg contents of 8–20 mol%. In this composition range, the presence of MgO leads to a suppression of carbon formation, especially when compared to Ni supported on Mg-free zirconia. According to their activity and stability depending on the Ni- and Mg-contents, the catalysts were assigned to three categories: (I) low activity and high stability, (II) high activity and some stability and (III) high activity, but low stability.

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