Synthesis and characterization of the flower-like LaxCe1−xO1.5+δ catalyst for low-temperature oxidative coupling of methane

Abstract

Lanthanum-based oxides are promising candidates for low-temperature oxidative coupling of methane (OCM). To further lower the OCM reaction temperature, the Ce doped flower-like La2O2CO3 microsphere catalysts were synthesized, achieving a significantly low reaction temperature (375 °C) while maintaining high C2+ hydrocarbon selectivity (43.0%). Doping Ce into the lattice of La2O2CO3 created more surface oxygen vacancies and bulk lattice defects, which was in favor of the transformation and migration of oxygen species at 350–400 °C. The designed H2 temperature-programmed reduction (H2-TPR) experiments provided strong evidence that the low reaction temperature of LaxCe1−xO1.5+δ can be attributed to the transformation and migration of oxygen species, which dynamically generated surface oxygen vacancies for continuous oxygen activation to selectively convert methane. Moreover, designed temperature-programmed surface reaction (TPSR) clarified that two kinds of surface oxygen species in LaxCe1−xO1.5+δ catalysts were concerned with catalytic performance, that is, the surface chemisorbed oxygen species for the activation of CH4 and the formation of CH3• intermediates, surface La-Ce-O lattice oxygen species that caused the excessive oxidation of CH3• intermediates. Finally, the factors affecting the transformation and migration of oxygen species were explored.