Evidence for redispersion of Ni on LaMnO₃ films following high-temperature oxidation

LaMnO₃ films, 0.5-nm thick, were deposited by atomic layer deposition (ALD) onto γ-Al₂O₃ that had been modified with 15- wt% CaO. The CaO was shown to be effective in preventing formation of LaAlO₃ that formed when La₂O₃ was deposited directly onto γ-Al₂O₃. Lattice fringes on the resulting CaAl₂O₄/γ-Al₂O₃ substrate were weakly resolved, allowing a detailed characterization of the LaMnO₃ films. High-resolution transmission electron microscopy (HR-TEM) images showed that the LaMnO₃ formed two-dimensional crystallites, ∼10–15 nm wide, that covered most of the surface. Crystallites with (0 0 1) and (1 1 1) orientation were clearly identified. High-temperature oxidation caused Ni to spread over the LaMnO₃ film, suggesting there is a reaction of the Ni²⁺ cations with the perovskite lattice. Ni formed by high-temperature reduction on these films remained well dispersed and significantly more active for CO₂ reforming of CH₄ compared to Ni on MgAl₂O₄, even after repeated oxidation and reduction cycles at 1073 K. The implications of these results for understanding metal-support interactions between Ni and LaMnO₃ are discussed.