Monopropellant decomposition catalysts.: V.: Thermal decomposition and reduction of permanganates as models for the preparation of supported MnOx catalysts

The need for highly concentrated hydrogen peroxide solutions to fuel spacecraft propulsion systems necessitates the development of new catalytic formulations mainly based on supported manganese oxides. In order to improve the preparation of such catalysts, the thermal decomposition and the hydrothermal reduction of different permanganate precursors were studied, as well as the effect of washing on the products. The test samples were characterized by X-ray power diffraction (XRD) and surface area determination, and compared for their catalytic activity towards H2O2 decomposition using a constant pressure reactor (for 1.71% H2O2) and a constant volume reactor (for 50% H2O2). The catalysts prepared by thermal decomposition of KMnO4 or (NaMnO4H2O)-H-. have shown the intermediate formation of potassium (or sodium) manganate, and its partial dissolution during washing with water; higher catalytic activity and larger surface area were observed for the decomposition products of KMnO4. The hydrothermal reduction yielded products exhibiting larger surface area and higher specific catalytic activity when carried out under stoichiometric conditions. Comparable kinetic parameters were determined using both Catalytic reactors. Unsupported and alumina supported catalysts displayed comparable activity per gram of manganese. (C) 2002 Elsevier Science B.V. All rights reserved.