Microscopic insights into the reaction mechanism of Fe-based oxygen carrier with CH4 in chemical-looping combustion

Fe-based oxygen carriers are regarded as a promising class of oxygen carriers in the field of chemical looping combustion. However, the elucidation of the detailed microscopic reaction mechanism of oxygen carriers remains a significant challenge. In this work, we combine in situ spectroscopy, density-functional theory (DFT) calculations, and micro-kinetic modelling to reveal the microscopic reaction mechanism of CH 4 combustion on α-Fe 2 O 3 . The macroscopic reaction characterization of hematite with CH 4 was carried out on a fixed bed, and gas chromatography (GC) was utilized to detect the combustion products (CO 2 , H 2 O and H 2 ). Subsequently, in situ spectroscopy and DFT were combined to reveal the detailed pathways for the CH₄ oxidation process. The results indicated that the reaction intermediates evolve from methoxy (CH 3 O*) to the bridged bidentate formate (b-HCOO*) to the monodentate formate (m-HCOO*), which ultimately leads to the formation of CO 2 through a combination of H transfer and lattice oxygen oxidation. A micro-kinetic model was developed which incorporates surface reaction with the oxygen transport. This revealed that CH 3 O* and CH 3 O* → CH 2 OO* are the key intermediates and radical reactions, respectively, for CO 2 production. The elucidation of the reaction mechanism may prove beneficial for the future development of novel Fe-based oxygen carriers.