Deoxidation of manganese oxides in supercritical N,N-dimethylformamide (SC-DMF) is revealed, contrasting to previous amounts of reports on supercritical water oxidation. Mn3O4 and MnO can be produced by the reaction starting from layered manganese oxides (delta-MnO2) in a uniform supercritical process. Time effect can give rise to the transition to Mn3O4 under low temperature, but the prolonged time, under a temperature lower than 200 degrees C, cannot cause this transition. Phase diagram is obtained, including three regions of MnO2, Mn3O4 and MnO as the main material phase. The completion of transition accompanies with an oxygen loss course. Comparison between supercritical oxidation of water and supercritical deoxidation of organic DMF demonstrates the unique mechanisms of supercritical processing. In terms of the surface contacting fluid, deoxidation kinetics has a reciprocal law of growing size for manganese oxides. The new deoxidation procedure using organic solvent is proposed for the processing of metal oxides. (C) 2014 Elsevier B.V. All rights reserved.