期刊
ACS CATALYSIS
卷 7, 期 12, 页码 8653-8663出版社
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.7b02595
关键词
Ba-Fe perovskites; oxygen vacancies; CO oxidation; activation pretreatments; aberration-corrected electron microscopy; in situ diffraction techniques
资金
- MINECO (Spain) [MAT2014-54372-R, MAT2013-40823-R, CSD2009-00013]
- Ramon y Cajal Fellowships Program of MINECO [RYC-2012-10004]
A BaFeO3-delta (delta approximate to 0.22) perovskite was prepared by a sol gel method and essayed as a catalyst in the CO oxidation reaction. BaFeO3-delta (0.22 <= delta <= 0.42) depicts a 6H perovskite hexagonal structural type with Fe in both III and IV oxidation states and oxygen stoichiometry accommodated by a random distribution of anionic vacancies. The perovskite with the highest oxygen content, BaFeO2.78, proved to be more active than its lanthanide-based counterparts, LnFeO(3) (Ln = La, Sm, Nd). Removal of the lattice oxygen detected in both temperature-programmed oxidation (TPO) and reduction (TPR) experiments at around 500 K and which leads to the complete reduction of Fe4+ to Fe3+, i.e. to BaFeO2.5, significantly decreases the catalytic activity, especially in the low-temperature range. The analysis of thermogravimetric experiments performed under oxygen and of TPR studies run under CO clearly support the involvement of lattice oxygen in the CO oxidation on these Ba-Fe perovskites, even at the lowest temperatures. Atomically resolved images and chemical maps obtained using different aberration-corrected scanning transmission electron microscopy techniques, as well as some in situ type experiments, have provided a clear picture of the accommodation of oxygen nonstoichiometry in these materials. This atomic scale view has revealed details of both the cation and anion sublattices of the different perovskites that have allowed us to identify the structural origin of the oxygen species most likely responsible for the low-temperature CO oxidation activity.
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