Influence of metal oxides on the performance of Pd/Al2O3 catalysts for methane combustion under lean-fuel conditions

Pd/Al2O3 catalysts modified by different metal oxides (Mn, Fe, La, Mg and Ni oxides) were prepared and tested for fuel-lean methane/air catalytic combustion. It was found that the support material influenced the combustion performance significantly. The addition of NiO or MgO effectively improved the activity and hydrothermal stability of catalysts. X-ray diffraction (XRD) results showed the presence of spinel phase in the Pd/Al2O3–NiO and Pd/Al2O3–MgO catalysts. Temperature-programmed desorption of ammonia (NH3-TPD) measurements indicated that the supports became weakly acidic because of the formation of NiAl2O4 or MgAl2O4 spinel. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed the well dispersion of Pd particles on the Al2O3–NiO and Al2O3–MgO supports. It was concluded that the formation of the NiAl2O4 or MgAl2O4 spinel phase during preparation would be beneficial for the methane catalytic performance of Pd catalysts.

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► Catalysts for methane combustion under lean-burn conditions
► Addition of Ni or Mg oxide improves the catalytic performance of Pd/Al2O3.
► Aluminate spinels are formed after adding Ni or Mg oxide to the supports.
► Aluminate spinels weaken the acidity of support and prevent oxidation of Pd.
► Support with spinel phase stabilizes Pd against aggregation during reaction.