Lattice oxygen transport and structural evolution of oxygen carriers for chemical looping reforming: A review of mechanisms, challenges, and regulation strategies

This review focuses on lattice oxygen transport and the dynamic structural evolution of oxygen carriers in chemical looping reforming (CLR), highlighting their roles in oxygen transfer, product selectivity, and redox stability. In CLR, lattice oxygen serves as an internal oxygen shuttle, enabling spatially or temporally separated reduction and reoxidation, while oxygen carrier performance is governed by its activity, mobility, and regenerability. Excessive surface lattice oxygen promotes nonselective deep oxidation, whereas insufficient or sluggish oxygen replenishment limits redox conversion and accelerates carbon deposition. These limitations are often accompanied by vacancy accumulation, cation migration, phase separation, and structural degradation during redox cycling. Although in situ and operando characterization has advanced the understanding of lattice oxygen migration and oxygen carrier evolution, comprehensive reviews of lattice oxygen transport and its regulation in CLR remain scarce. This review summarizes recent advances in dynamic structural evolution, in situ/operando characterization, and multiscale regulation strategies. Particular emphasis is placed on the Kirkendall effect, vacancy aggregation, phase separation, interfacial reconstruction, and metal exsolution, as well as their impacts on lattice oxygen migration and metal-oxide interfaces. Strategies including multicomponent doping, defect engineering, and core-shell, yolk-shell, and exsolution structures are discussed for enhancing oxygen transport, suppressing sintering, and improving coking resistance. Overall, this review establishes the structure-oxygen transport-reaction relationship as a guiding principle for designing efficient and durable oxygen carriers.