The reduction and oxidation behaviour of manganese oxides

The reduction of manganese oxides with methane was studied to investigate the suitability of manganese as an oxygen storage compound. Manganese oxides are reduced by CH4 to a lower-valent manganese oxide, producing CO2 and water. Once the manganese oxide is reduced, it can be regenerated, i.e. reoxidised. By integrating this exothermic oxidation cycle with endothermic methane reforming, a new setup for exothermic, small scale syngas production is obtained. Manganese oxides can be reduced to manganese(II) oxide with methane at temperatures higher than 723 K. Reoxidation of MnO at 823 K leads to the formation of Mn2O3 at 823 K. At 1073 K reoxidation of MnO gives Mn3O4, which corresponds to a lower Mn-valency than expected thermodynamically. Subsequent oxidation-reduction cycles lead to an increase in reduction temperature, probably due to a higher crystallinity. (C) 1999 Elsevier Science B.V. All rights reserved.