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 La_0.7Fe_0.7Mn_0.3O₃, uncovering a heterogeneous defect landscape that governs its activity in reducing NO by CO. We identified a layer of La_0.7-<i>x</i>Fe_0.7Mn_0.3O₃ 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 LaFe_0.7Mn_0.3O₃. These confined defect layers stabilize catalytically active sites, enabling the formation of FeO_<i>x</i> 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 FeO_<i>x</i> 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.