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 gamma-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 gamma-Al2O3. Lattice fringes on the resulting CaAl2O4/gamma- 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 twodimensional crystallites,similar to 10-15 nm wide, that covered most of the surface. Crystallites with (001) and (111) 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. Published by Elsevier Inc.

Automated summary

LaMnO3 films with a thickness of 0.5 nm were successfully deposited on CaO-modified γ-Al2O3 substrate using atomic layer deposition (ALD) method. The presence of CaO effectively prevented the formation of LaAlO3 when depositing La2O3 directly onto γ-Al2O3. The LaMnO3 films exhibited two-dimensional crystallites with a size of approximately 10-15 nm. At high temperatures, oxidation caused Ni to spread over the LaMnO3 film, while the Ni formed by high-temperature reduction remained well dispersed and showed higher activity for CO2 reforming of CH4 compared to Ni on MgAl2O4. These results have important implications for understanding the metal-support interactions between Ni and LaMnO3.