Abstract
The support material can play an important role in oxidation catalysis, notably for CO oxidation. Here, we study two materials of the Brownmillerite family, CaFeO2.5 and SrFeO2.5, as one example of a stoichiometric phase (CaFeO2.5, CFO) and one existing in different modifications (SrFeO2.75, SrFeO2.875 and SrFeO3, SFO). The two materials are synthesized using two synthesis methods, one bottom-up approach via a complexation route and one top-down method (electric arc fusion), allowing to study the impact of the specific surface area on the oxygen mobility and catalytic performance. CO oxidation on 18O-exchanged materials shows that oxygen from SFO participates in the reaction as soon as the reaction starts, while for CFO, this onset takes place 185 °C after reaction onset. This indicates that the structure of the support material has an impact on the catalytic performance. We report here on significant differences in the catalytic activity linked to long-term stability of CFO and SFO, which is an important parameter not only for possible applications, but equally to better understand the mechanism of the catalytic activity itself.
Highlights
Catalytic consumption of reactants (CO) oxidation on perovskites usually follows a suprafacial mechanism involving surface oxygen [1]
Our results clearly demonstrate the importance of the synthesis conditions for a given system, together with the existence or not of oxygen non-stoichiometry to better understand its catalytic activity and stability in oxidation reactions
The facilitated oxygen mobility directly translates into superior CO oxidation performance, indicated by CO oxidation taking place at lower temperatures for both SFO materials compared to the corresponding CFO material
Summary
Catalytic CO oxidation on perovskites usually follows a suprafacial mechanism involving surface oxygen [1]. While perovskites have been extensively studied for oxidation reactions, less work is available on reduced perovskites such as the Brownmillerite family ABO2.5 [3,4,5,6]. The first works date 40 years back, when Shin et al studied the decomposition of NO over the two BBrownmillerites CaFeO2.5 and SrFeO2.5. SrFeO2.5 is active, while CaFeO2.5 remains inactive under the studied reaction conditions. This difference has been attributed to the structural difference of the two materials, with disordered oxygen vacancies at high temperatures for SrFeO2.5 as opposed to the ordered vacancies in CaFeO2.5. The best-performing material is the Brownmillerite with a Ca/Fe ratio of 1. The better performance of CaFeO2.5 is ascribed to the presence of active oxygen species O2− on the surface
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