Enhanced Oxidative Coupling of CH ₄ to Olefins via CO ₂ Assistance over Alkali Metal-Supported Perovskite

Methane oxidative coupling (OCM) based on the chemical-looping (CL) concept represents a promising pathway for the high-value upgrading of methane; however, commercialization is hindered by low olefin yields and deactivation of the oxygen carrier. In this study, we demonstrate that CO2 assistance significantly improves the performance of Li2CO3-promoted perovskite oxygen carriers in CL-OCM. The methane conversion increases from 22.7% to 30% and C2 selectivity increases from 50% to 89.6% when 10% of CO2 was introduced, while maintaining stable performance over 50 consecutive cycles. The presence of CO2 stabilizes the crystalline phase of the oxygen carrier. By maintaining the lattice oxygen concentration via a synergistic oxygen replenishment mechanism, the oxygen carrier achieves enhanced and durable catalytic activity. 13C isotopic labeling experiments elucidate the conversion pathways of CH4 and CO2, and 18O isotope tracing further confirms a surface lattice-oxygen exchange mechanism between CO2 and the oxygen carrier. These findings provide a viable strategy for advancing the commercialization of OCM and enabling the efficient synergistic utilization of CH4 and CO2.