Role of Copper Migration in Nanoscale Ageing of Supported CuO/Al ₂ O ₃ in Redox Conditions: A Combined Multiscale X‐ray and Electron Microscopy Study

Abstract Chemical Looping Combustion is a promising midterm solution to mitigate CO 2 emission, by carrying out indirect fuel combustion and allowing inherent separation of CO 2 . During the CLC process, an oxygen carrying material is subjected to successive oxidation‐reduction reactions at high temperature which induce significant material degradation. CuO/Al 2 O 3 based materials have been widely considered as promising oxygen carriers (OC). However, the oxygen carrier ageing mechanisms (active phase migration and interactions with the support, phase transitions) are not well understood. Herein, an in‐depth overview of the material evolution is achieved by employing a multi‐scale characterization approach. At the μm‐scale, copper migration within the alumina support has been observed using Scanning Transmission X‐ray Microscopy (STXM) and Scanning Electron Microscopy (SEM). The spatial distribution of the Cu−Al species provides information on copper mobility and the different phases interactions. A comprehensive mechanism is proposed concerning the redox behaviour of the CuO/Al 2 O 3 system, relating the diffusion of the Cu‐species, the active phase‐support interactions, and the role of copper in the Al 2 O 3 support phase transition to the temperature and the number of redox cycles. Understanding the ageing process of CuO/Al 2 O 3 materials paves a way to design more stable oxygen‐carriers.