(135d) 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