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Main Title: Cyanamide route to calcium-manganese oxide foams for water oxidation
Author(s): Baktash, Elham
Zaharieva, Ivelina
Schröder, Marc
Goebel, Caren
Dau, Holger
Thomas, Arne
Type: Article
Language Code: en
Abstract: In nature, photosynthetic water oxidation is efficiently catalysed at a protein-bound μ-oxido Mn4Ca cluster. This cluster consists of earth abundant, non-toxic elements and serves as a paragon for development of synthetic catalysts. In this study we developed porous calcium–manganese oxides with a unique foam-like nanostructure prepared via a facile and robust synthetic route using cyanamide as a porogen. A series of such oxide foams annealed at different temperatures was characterized by TEM, SEM, XRD, N2 physisorption, and X-ray absorption spectroscopy (XAS) in order to correlate crystallinity, atomic structure, surface area and oxidation state of the materials with catalytic activity. Some of the resulting Ca–Mn oxides show high activity as catalysts for water oxidation in the presence of cerium(IV) ammonium nitrate as a non-oxo transfer oxidant. An amorphous calcium–manganese-oxide foam with 130 m2 g−1 surface area and Mn oxidation state of +3.6 was identified to be most active; its activity is superior to previously reported Ca–Mn oxides. At the atomic level, this material shares structural motifs with the biological paragon as revealed by dual-edge XAS at the Mn and Ca K-edge. Rather than nanostructure and surface area, the atomic structure of the Ca–Mn oxide and the extent of structural order appear to be crucial determinants of catalytic activity. Fully disordered low-valent Mn materials as well as high-valent but crystalline Mn–Ca oxides are unreactive. Highly disordered variants of layered manganese oxide with Ca and water molecules interfacing layer fragments are most reactive.
Issue Date: 2013
Date Available: 24-Jun-2016
DDC Class: 540 Chemie und zugeordnete Wissenschaften
Sponsor/Funder: DFG, EXC 314, Unifying Concepts in Catalysis
Journal Title: Dalton transactions : a journal of inorganic chemistry, including bioinorganic, organometallic, and solid-state chemistry
Publisher: Royal Society of Chemistry
Publisher Place: Cambridge
Volume: 42
Issue: 48
Publisher DOI: 10.1039/c3dt51693h
Page Start: 16920
Page End: 16929
EISSN: 1477-9226
Notes: Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.
Appears in Collections:Inst. Chemie » Publications

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