Oxidative transformation of methane over nickel catalysts supported on rare-earth metal oxides

The oxidative transformation of methane over Ni catalysts supported on La, Sm and Ce oxides was investigated at atmospheric pressure, T=723–923 K and CH₄/O₂=1–10. The BET surface areas were low (3–22 m² g⁻¹) and decreased strongly after reaction (down to 0.5  m² g⁻¹). Carbonate species, Ni₂O₃ and supported oxides were identified by XRD or IR spectroscopy studies in both the fresh and used catalysts. The Ni° phase was also probably formed as amorphous phase. The oxidative coupling of methane route passed through a minimum as a function of the Ni percentage and was favored by the Ce or Sm oxide support, Li additive and low reaction temperature. High selectivities (60–90%) and good yields (about 15%) in C₂ hydrocarbons with low carbon balance (0–10%) were obtained at 823 K. La supported oxide, Ba additive and high reaction temperature favored the partial oxidation of methane. The obtained results were discussed in the light of the reducibility and acid–base properties of the catalysts.