NDLI: Water-oxidation catalysis by synthetic manganese oxides – systematic variations of the calcium birnessite theme

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Frey, Carolin E. Kurz, Philipp Wiechen, Mathias
Description	Author Affiliation: Frey CE ( Institut für Anorganische und Analytische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, 79104 Freiburg, Germany. philipp.kurz@ac.uni-freiburg.de.)
Abstract	Layered manganese oxides from the birnessite mineral family have been identified as promising heterogeneous compounds for water-oxidation catalysis (WOC), a key reaction for the conversion of renewable energy into storable fuels. High catalytic rates were especially observed for birnessites which contain calcium as part of their structures. With the aim to systematically improve the catalytic performance of such oxide materials, we used a flexible synthetic route to prepare three series of calcium birnessites, where we varied the calcium concentrations, the ripening times of the original precipitates and the temperature of the heat treatment following the initial synthetic steps (tempering) during the preparation process. The products were carefully analysed by a number of analytical techniques and then probed for WOC activity using the $Ce^{4+}-system.$ We find that our set of twenty closely related manganese oxides shows large, but somewhat systematic alterations in catalytic rates, indicating the importance of synthesis parameters for maximum catalytic performance. The catalyst of the series for which the highest water-oxidation rate was found is a birnessite of medium calcium content (Ca:Mn ratio 0.2:1) that had been subjected to a tempering temperature of 400 °C. On the basis of the detailed analysis of the results, a WOC reaction scheme for birnessites is proposed to explain the observed trends in reactivity.
ISSN	14779226
Issue Number	11
Volume Number	43
e-ISSN	13645447
Journal	Dalton Trans.
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2014-03-21
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Calcium Chemistry Manganese Compounds Oxides Water Catalysis Oxidation-Reduction Chemical Synthesis Journal Article Research Support, Non-U.S. Gov't
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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