Critical Influence of Redox Pretreatments on the CO Oxidation Activity of BaFeO_3−δ Perovskites: An in-Depth Atomic-Scale Analysis by Aberration-Corrected and in Situ Diffraction Techniques

Abstract

A BaFeO 3−δ (δ ≈ 0.22) perovskite was prepared by a sol−gel method and essayed as a catalyst in the CO oxidation reaction. BaFeO 3−δ (0.22 ≤ δ ≤ 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, BaFeO 2.78 , 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 Fe 4+ to Fe 3+ , i.e. to BeFeO 2.5 , significantly decreases the catalytic activity, especially in the lowtemperature 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 atomicscale 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.

Exceptional Low-Temperature CO Oxidation over Noble-Metal-Free Iron-Doped Hollandites: An In-Depth Analysis of the Influence of the Defect Structure on Catalytic Performance

“…We have further investigated the location of Fe. The element distribution maps established from the EELS spectrum imaging experiments 59 reveal that the dopant predominantly substitutes Mn in the octahedral positions, in good agreement with the results of the ND Rietveld refinements.…”

“…We then establish structure–property correlations that could be used to provide the basic guidelines for the design of new promising catalysts. 4 , 59 …”

“…We then establish structure−property correlations that could be used to provide the basic guidelines for the design of new promising catalysts. 4,59 a ND: composition determined from neutron diffraction. b The cationic composition corresponds to that determined by EMPA, and the Mn 3+ content was interpolated in these cases using the Mn 3+ vs Fe 3+ dependency observed in the samples analyzed by neutron diffraction (see Figure S3).…”

Electronic Structure, Chemical Bonding, and Electrocatalytic Activity of Ba(Fe0.7Ta0.3)O3−δ Compounds

“…Therefore, a viable alternate low-cost electrocatalyst for HER as well as for ORR has attracted increasing interest in renewable energy research. In this direction, perovskite oxides of transition metals are considered as promising alternatives in this regard and hence activating and optimizing non-noble metals for HER is an alternative way for low-cost hydrogen production. ,,,− Non-precious-metal-based electrocatalysts also attracted intense attention as a suitable electrocatalyst toward ORR due to its high activity and better stability. − Therefore, in the present work, in addition to evaluating the structure and electronic properties of Fe, Ta co-doped oxide, we performed studies to evaluate the electrocatalytic activity toward HER and ORR.…”

“…Perovskite oxides, which constitute wide range of compositions, are earth-abundant and offer excellent means to realize chemical compounds, especially in the field of catalysis, that are economically viable and versatile in terms of technological or industrial applications. − The perovskite oxides find interesting applications in current and emerging electronics and electro-optics, − electrochemical science and technology, ,,− electromechanical sensors and systems, , solid oxide fuel cell technology, ,, electromagnetic devices and magnetic tunnel junctions, − , and solid-state memory device technologies. − ,− The perovskite oxide-based piezoelectric materials are attractive for a number of applications in micromechanics, sensors, actuators, optoelectronics, and energy-harvesting applications. ,,, Especially, the piezoelectric and ferroelectric properties, which often exist in the same perovskite oxide matrix, provide excellent means to harvest energy from multiple sources, which include mechanical, electrical, chemical, vibration, and optical . The dominance of oxide perovskites in the electromechanical and sensor technological applications and development is mostly due to their superior properties, such as high Curie temperature ( T c ≈ 390 °C), high dielectric constant (ε ∼ 20 000 at T c ), low dielectric loss (tan δ ∼ 0.004), and high piezoelectric coefficient ( d 33 ∼ 220 pC/N). − …”