Defect-Engineered Perovskites: Atomic Scale Nature of A-Site Vacancy-Stabilized Catalytically Active Phase.

Using aberration-corrected electron microscopy and spectroscopy, we reveal the atomic scale structure and catalytic function of the A-site-deficient perovskite La0.7Fe0.7Mn0.3O3, uncovering a heterogeneous defect landscape that governs its activity in reducing NO by CO. We identified a layer of La0.7-xFe0.7Mn0.3O3 that is highly A-site-deficient. This layer is just two to three unit cells thick at the surfaces and the interfaces of the perovskite particles and transitions toward the bulk into stoichiometric LaFe0.7Mn0.3O3. These confined defect layers stabilize catalytically active sites, enabling the formation of FeOx inclusions ranging from approximately 1  nm to several nanometers in size at the surfaces. In situ surface characterization and catalytic measurements reveal that these interfacial FeOx nanoparticles serve as active sites during the NO reduction by CO via the Mars-van Krevelen mechanism. Our findings establish a direct relationship between the structure and properties of nanoscale A-site nonstoichiometry and redox-driven catalytic activity. This relationship offers a new design strategy for tailoring reactivity through defect engineering.