Selective Oxidative Coupling of Methane Over Rare Earth-Modified Bi2O3 Catalyst

Abstract

Abstract. The oxidative coupling of methane (OCM) offers a direct route to transform methane into valuable C2 hydrocarbons, yet the challenge of achieving high selectivity while maintaining catalyst stability persists. Herein, a Bi1.5Y0.3Sm0.2O3 (BYS) catalyst was synthesized via the citrate sol–gel method and comprehensively characterized by X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray spectroscopy. The results confirmed a single-phase cubic fluorite structure with well-dispersed elements, providing high oxygen-ion mobility and redox stability. Catalytic testing revealed that the CH4:O2 ratio strongly governs reaction pathways. At 4:1, the BYS catalyst exhibited the highest C2 yield and selectivity, balancing methane activation with suppression of total oxidation. A methane-rich ratio (5:1) favored CO formation and carbon deposition, while an oxygen-rich ratio (3:1) promoted deep oxidation to CO2. Temperature variation further highlighted an optimal window around 740–750 °C, maximizing C2 selectivity and the C2H4/C2H6 ratio by favoring dehydrogenation. These findings underline the significance of rare-earth doping in stabilizing the fluorite lattice, enhancing oxygen vacancy concentration, and steering the OCM reaction toward C2 hydrocarbons.