Mechanochemical reduction of manganese dioxide by grinding in organic vapors

概要

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Mechanochemical redox reactions of manganese dioxide with organic vapors have been studied to control the chemical valence (oxidation number) of manganese ions under grinding. Electrolytic-manganese dioxide (EMD) including double chains of edge-sharing MnO6-octahedra transforms into β-MnO2 (Pyrolusite) consisting of the single chains under grinding in Ar. The mechanical dissociation of the double chains generates active sites to adsorb the atmospheric (CH3)2CO vapor and the strongly adsorbed (CH3)2CO molecules pull out the oxide ions from MnO2 to reduce Mn4+ to Mn3+ ions, while (CH3)2CO is oxidized to CO2 and H2O via the intermediate oxidation products, HCOH and CH3COH. One (CH3)2CO molecule can reduce 16 MnO2 units to trivalent MnO1.5 (Bixbyite). However, the decomposition products, CO2 and H2O, occupying the adsorption sites dominantly to (CH3)2CO disturb the redox process. This mechanochemical reduction of MnO2 can be applied to the synthesis of LiMnIIIMnIVO4 powder from both combinations of the starting mixtures of MnO2-LiOH and MnO2-Li2CO3. Some alcohols and ketones also provide the similar reduction ability.
2009-09-01