Effects of Mg, Ca, Sr, and Ba Dopants on the Performance of La2O3 Catalysts for the Oxidative Coupling of Methane

Oxidative coupling of methane (OCM) is a reaction to directly convert methane into high value-added hydrocarbons (C2+) such as ethylene and ethane using molecular oxygen and a catalyst. This work investigated lanthanum oxide catalysts for OCM, which were promoted with alkaline-earth metal oxides (Mg, Ca, Sr, and Ba) and prepared by the solution-mixing method. The synthesized catalysts were characterized using X-ray powder diffraction, CO2-programmed desorption, and X-ray photoelectron spectroscopy. The comparative performance of each promoter showed that promising lanthanum-loaded alkaline-earth metal oxide catalysts were La-Sr and La-Ba. In contrast, the combination of La with Ca or Mg did not lead to a clear improvement of C2+ yield. The most promising LaSr50 catalyst exhibited the highest C2+ yield of 17.2%, with a 56.0% C2+ selectivity and a 30.9% CH4 conversion. Catalyst characterization indicated that their activity was strongly associated with moderate basic sites and surface-adsorbed oxygen species of O-2(-). Moreover, the catalyst was stable over 25 h at a reactor temperature of 700 degrees C.

Automated summary

This study investigated lanthanum oxide catalysts promoted with alkaline-earth metal oxides for the oxidative coupling of methane (OCM). The results showed that La-Sr and La-Ba catalysts performed well, with high C2+ yield and selectivity. In contrast, the combination of La with Ca or Mg did not lead to significant improvement in yield. The activity of the catalysts was strongly related to moderate basic sites and surface-adsorbed oxygen species of O-2(-), and they exhibited good stability under high-temperature conditions.