Development of Stable Multiphase Ni-Mgx-Aly-O Catalysts for CO2 Reforming of Methane

  Development of stable multiphase Ni-Mg_xAl_yO catalysts for CO₂ reforming of methane

J. Zhang^a, Q. J. Chen^a, B. R. Pan^a, W. B. Kong ^a, Q. W. Jin^a, T.J. Zhao*^a,          Y. H. Sun*^a,b

a: Low Carbon Energy Conversion Center, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201203, China

b: State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, Shanxi, China

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Abstraction:

CO₂ reforming of methane to produce synthesis gas is becoming more research attractive due to the increasing interest in reduction of carbon dioxide emissions and more efficient utilization of natural gas. From an industrial standpoint, Ni-based catalysts have drawn significant research attention for their high activity and wide availability. However, metal sintering, oxidation, and especially significant carbon formation result in the severe deactivation of the Ni catalysts. Some catalysts such as NiO/MgO solid solution, Ni/Al₂O₃, NiAl₂O₄ spinel, etc. were reported to have excellent performance for CO₂ reforming of methane. However, those kinds of catalysts still have their own disadvantages, for example, hydrophobia of  NiO/MgO, low active site dispersion for Ni/ Al₂O₃, difficult reduction for NiAl₂O₄ spinel, etc.

Fig .1 XRD for Ni-Mg_xAl_yO catalysts         Fig .2 Stability of Ni-Mg_xAl_yO for CO₂ reforming of methane

In this work, a high stable multiphase Ni-Mg_xAl_yO catalyst for CO₂ reforming of methane was developed by HT precursors. For comparison, NiO/MgO solid solution, Ni/Al₂O₃, and NiAl₂O₄ spinel catalysts were also prepared and tested. The Catalysts were characterized using ICP-MS, BET, XRD, H2-TPR, TEM, and TG. Catalysts screening for the carbon dioxide reforming of methane showed that Ni-Mg_xAl_yO catalysts with multiphase (periclase-spinel) obtained by hydrotalcite-type (HT-type) precursors exhibited superior performance to other Ni–Mg–Al–O catalysts with different phases. This special multiphase catalyst exhibits very high and stable activity over 1000 h without deactivation at a GHSV of 79, 000 ml/(hg) at 850 ^oC. Both commercial Ni/Al₂O₃ catalyst and the NiO/MgO solid solution with single periclase phase deactivated quickly after the ignition of reaction, and the NiAl₂O₄ spinel show less activity for their low reductively.  BET, XRD and H2-TPR  results indicated that the activity of  the catalysts were strongly depended on the structures, the sizes of the nanoparticles, surface area and active site dispersion. In fact, those characteristics are strongly depended on the types of the phases in the catalyst, and the interaction between them. It was believed that the synergy between periclase and spinel could also significantly improve catalyst performance and reduce carbon formation. A high metal dispersion or small ensemble size can be obtained by NiO/MgO solid solution. The excellent stability of metal was enhanced by spinel phase exist in the NiO/MgO solid solution, which further promoted the metal dispersion and resistance of metal sintering. The synergistic effects between crystal phases and phase cooperation, the phenomena responsible for the variation of activity in the methane reforming as a function of the degree of spinel substitution in periclase were deeply discussed.

Keywords : Natural gas; CO₂ Methane reforming; Ni-Mg_xAl_yO multiphase catalysts; phase cooperation