CO2-Assisted Oxygen Exchange to Enhance the Chemical Looping Oxidation Coupling of Methane

The production of olefins via the oxidative coupling of methane (OCM) has been extensively studied. However, the inherent “trade-off” in the OCM limits ethylene yield and selectivity. CO2-assisted OCM provides an opportunity to overcome this limitation by using CO2 as a weak oxidant. Here, we reported a CO2-assisted chemical looping oxidative coupling of methane (CO2–CLOCM) approach using MnO–Na2WO4/SiO2 as the oxygen carrier. The results demonstrated that MnO–Na2WO4/SiO2 manifested superior catalytic performance, achieving 14.29% methane conversion, 0.6224 mmol·g–1·h–1 C2+ production rate, and 3.01% CO2 conversion. Compared to the CLOCM reaction without CO2 assistance, the methane conversion recorded a relative increase of 26.57%, the C2+ production rate showed a relative increase of 21.37%, and the olefin purity in the product increased from 53% to 81%. Introduction of CO2 regulated oxygen release kinetics during the CLOCM process, replenishing lattice oxygen on the oxygen carrier and thereby enhancing methane conversion and C2+ production rates. At elevated temperatures, competitive interactions between CH4 and CO2 for active sites became evident, manifesting ″trade-off ″ in their respective conversion. Isotope-labeling experiments conducted to investigate the CH4–CO2 reaction pathways revealed intricate interactions on the oxygen carrier’s surface, where CO2 engages in thorough oxygen exchange with the carrier.