Nanometric nickel exsolution in the hexagonal perovskite Ba8Ta6NiO24: Survey of the structural, magnetic and catalytic features
Résumé
Nickel nanoparticles that decorate the surface of a parent oxide are well known to be developed by some cubic-type perovskites from the exsolution of their intrinsic Ni 2+ species in reducing conditions with subsequent catalytic properties. In this work, we show similar phenomenon in a hexagonal-type perovskite. The reducing treatment in ammonia of Ba 8 Ta 6 NiO 24 , a hexagonal perovskite-type oxide, leads to the exsolution of Nickel nano-sized particles at the surface of the precursor leaving oxygen vacancies and partially depleted but rearranged Ni/Ta sites. Spectroscopic methods, X-ray diffraction, TEM and TGA were employed to investigate the Ni exsolution while TGA was used to investigate the thermal behavior and its reversibility. 50 % of the initial nickel content transferred into Ni 0 nanoparticles as determined from M(H) magnetization plots and TGA, in agreement with the concomitant creation of oxygen vacancies in the preserved Ni 2+ coordination (50 %). The cationic vacancies (V c) involve face-sharing octahedral dimers in which Ni/Ta/V c rearranged through the shared face window, but preserves a non-centrosymmetric cationic partition. Ni exsoluted oxides often show a catalytic activity; we present here an original example of a hexagonal perovskite with catalytic activity toward syngas production by reforming of methane with carbon dioxide.
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Pussacq et al_2018_Nanometric nickel exsolution in the hexagonal perovskite Ba8Ta6NiO24.pdf (4.5 Mo)
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