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  Surface Conditions That Constrain Alkane Oxidation on Perovskites

Koch, G., Hävecker, M., Teschner, D., Carey, S. J., Wang, Y., Kube, P., et al. (2020). Surface Conditions That Constrain Alkane Oxidation on Perovskites. ACS Catalysis, 10, 7007-7020. doi:10.1021/acscatal.0c01289.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-C773-8 Version Permalink: http://hdl.handle.net/21.11116/0000-0006-C786-2
Genre: Journal Article

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 Creators:
Koch, Gregor1, Author
Hävecker, Michael1, Author
Teschner, Detre1, Author
Carey, Spencer J.1, Author
Wang, Yuanqing1, Author
Kube, Pierre1, Author
Hetaba, Walid1, Author
Lunkenbein, Thomas1, Author
Auffermann, Gudrun2, Author              
Timpe, Olaf1, Author
Rosowski, Frank1, Author
Schlögl, Robert1, Author
Trunschke, Annette1, Author
Affiliations:
1External Organizations, ou_persistent22              
2Gudrun Auffermann, Inorganic Chemistry, Max Planck Institute for Chemical Physics of Solids, Max Planck Society, ou_1863432              

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Free keywords: AP-XPS, catalysis, NEXAFS, operando, oxygen species, selectivity
 Abstract: The crystal structure of perovskites can incorporate a wide variety of cations, which makes this class of materials so interesting for studies of links between solid-state chemistry and catalysis. Perovskites are known as typical total combustion catalysts in hydrocarbon oxidation reactions. The fundamental question that we investigate here is whether surface modifications of perovskites can lead to the formation of valuable reaction products in alkane oxidation. We studied the effect of segregated two-dimensional surface nanostructures on selectivity to propene in the oxidative dehydrogenation of propane. Manganese-based perovskites AMnO3 (A = La, Sm) were prepared by combustion and hydrothermal synthesis. Bulk and surface structures were investigated by X-ray diffraction, temperature-programmed reduction, aberration-corrected scanning transmission electron microscopy (STEM), multiwavelength Raman, and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) in combination with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Surface oxygen species responsible for C-H activation were distinguished by AP-XPS on the basis of a rigorous in situ analysis of the O 1s spectra recorded under a broad range of reaction conditions. Signals at 529.2, 530.1, 530.9, 531.2, and 531.8 eV were attributed to lattice O, defect-affected O, surface O, oxygen in carbonates, and hydroxyl groups, respectively. Operando AP-XPS revealed critical surface features, which occur under catalyst operation. The catalyst performance depends on the synthesis technique and the reaction conditions. In presence of a two-dimensional MnOx surface phase, addition of steam to the feed resulted in an increase in selectivity to the partial oxidation product propene to practically relevant values. The selectivity increase is related to the presence of Mn in a low oxidation state (2+/3+), an increased concentration of hydroxyl groups, and a higher abundance of adsorbed activated oxygen species on the catalyst surface. The surface analysis of a working catalyst highlights the importance of the termination layer of polycrystalline perovskites as a genuine property implemented by catalyst preparation. Such a termination layer controls the chemical properties and reactivity of perovskites. The information provides input for the development of realistic models that can be used by theory to predict functional properties. Copyright © 2020 American Chemical Society.

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Language(s): eng - English
 Dates: 2020-05-292020-05-29
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.1021/acscatal.0c01289
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Title: ACS Catalysis
  Abbreviation : ACS Catal.
Source Genre: Journal
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Publ. Info: Washington, DC : ACS
Pages: - Volume / Issue: 10 Sequence Number: - Start / End Page: 7007 - 7020 Identifier: ISSN: 2155-5435
CoNE: https://pure.mpg.de/cone/journals/resource/2155-5435