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The oxygen mobility and exchange are fundamental properties of perovskite oxides which regulate their application in catalysis, sensing, energy conversion and information technology [1]. The increasing need of sustainable catalytic materials has driven the development of nanoporous perovskite structures with improved surface reactivity [2,3]. Although it is intuitive that enhanced specific surface area (SSA) might improve the catalytic activity, it is not clear yet how this increase influences oxygen release and mobility in nanostructured grains and what is its effect on catalysis.
In the present paper, we investigate the role of porosity on the oxygen release of mesoporous perovskite oxides and demonstrate how the combination of these two parameters affects methane and carbon monoxide oxidation. We prepared mesoporous SrTi0.65Fe0.35O3-δ perovksites with SSA ranging from 45 to 80 m2/g via a template-free approach [2]. Combining thermal analyses with in situ synchrotron X-ray diffraction under Ar-atmosphere we showed that the material with least porosity does not release surficial oxygen species as the more porous counterparts. Instead much larger desorption of lattice oxygen is observed, as result of the larger lattice strain and higher Fe(IV) concentration.
This had significant effects on the catalytic performance of the materials. For low-temperature reactions as the CO oxidation the highly porous perovskite shows better performance due to the higher SSA and larger surface defect concentration. In case of high temperature reactions as methane combustion, the contribution of lattice oxygen is more relevant and the least porous material achieves the same performance as the high porous systems.
Hence, even though nanoporosity is usually considered beneficial for catalysis applications, mere maximization of the SSA is not necessarily of help and oxygen defect location (surface, bulk) and concentration need to be taken into account for the design of nanostructured catalysts.
References:
[1] Y. Cao, M. J. Gadre, A. T. Ngo, S. B. Adler, Dane D. Morgan, Nat. Commun. 2019, 10, 1346.
[2] B. Kayaalp, S. Lee, K. Klauke, S. Jongsu, L. Nodari, A. Kornowski, W. Jung, S. Mascotto, Appl. Catal. B Environ. 2019, 245, 536–545.
[3] B. Kayaalp, S. Lee, L. Nodari, J. Seo, S. Kim, W. Jung, S. Mascotto, ACS Appl. Nano Mater. 2020, acsanm.0c02456.
