Perovskite-derived MnOx/LaMnO3 nanocomposites to boost CO oxidation activity

In this study, the impact of nitric acid treatment parameters, specifically acid concentration and exposure time, on the morphological, redox, and catalytic properties of LaMnO3 for CO oxidation was thoroughly investigated. The samples were characterised by ICP analysis, N2 adsorption/desorption measurements, XRD, H2-TPR, XPS, HRTEM and HAADF-STEM. Acidic treatment of LaMnO3 significantly increases the surface area, creating a new porous structure. Under mild treatment conditions, the composition, crystal structure and morphology are also modified, resulting in MnOx/LaMnO3 catalysts with various Mn oxide species forming needle-like structures segregated on a highly defective La1-xMnO3-delta perovskite. These MnOx/LaMnO3 nanocomposites exhibited superior CO oxidation activity, achieving 10% CO conversion (T10) in the range of 375-396 K, compared to 459 K for the pristine perovskite. This enhanced performance is attributed not only to the increased surface area, but also to the exposure of reactive MnOx species on the surface of the perovskite and, crucially, to the interfacial synergism between MnOx and LaMnO3. This synergy enhances oxygen exchange, and it improves the reducibility of the nanocomposite at low temperatures, providing a better thermal stability of active phases at elevated temperatures. However, the benefits of the acid treatment are lost under more severe conditions that transform LaMnO3 into bulk Mn oxide phases (Mn2O3, Mn3O4), or pure MnO2, highlighting the critical role of MnOx/LaMnO3 interface properties for CO oxidation.