High-temperature phase evolution in CuO/Al2O3 oxygen carriers: insights from in situ quick XAS

Abstract

This study investigates phase transitions in CuO/Al₂O₃ oxygen carriers during chemical looping combustion (CLC), aiming to understand performance and stability over extended redox cycles. In situ quick X-ray assorption spectroscopy (QXAS) was employed to track the transformations of the copper aluminate phase (Cu_xAl_yO₄) over 50 redox cycles in various oxidizing (2.5 to 21% O₂ in N₂) and reducing (H₂, CO, CH₄) environments. The study reveals that the oxygen carrier undergoes significant phase transitions, reaching a threshold where Cu_xAl_yO₄ predominantly converts to copper oxide and α-Al₂O₃, leading to irreversible structural modifications. Complementary SEM analysis further highlights morphological changes, such as particle growth prior to α-Al₂O₃ formation. This cycle-dependent phase evolution provides new insights into accelerated ageing mechanism involving the interplay between copper phase transformations and α-Al₂O₃ formation, which is critical for enhancing the durability of oxygen carriers in CLC applications.