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Hydrated oxides of manganese supported on magnesium hydroxide as catalysts for hydrogen peroxide decomposition

1972; Elsevier BV; Volume: 25; Issue: 2 Linguagem: Inglês

10.1016/0021-9517(72)90217-5

1090-2694

R. I. Razouk, G.M. Habashy, N.Ph. Kelada,

Catalytic Processes in Materials Science

Three catalytic systems were studied: Mn, supported on magnesium oxide; Mn, supported on magnesium hydroxide prepared by coprecipitation; and Mn, supported on magnesium hydroxide prepared by impregnation. The rate of decomposition of H2O2 was used as a measure of the catalytic activity of the catalysts. Results indicated that the use of MgO as a carrier for the manganese oxides gave a highly active catalytic system as compared with that of manganese oxides or magnesium oxide alone. The Mn-supported on Mg(OH)2 system proved to have a better catalytic activity and to give better experimental reproducibility than the oxide system. The catalyst prepared by impregnation was found to be more active than a similar one prepared by coprecipitation; in the latter the Mn(OH)2 is assumed to be fixed in the lattice of Mg(OH)2 so that the surface concentration of manganese is lower than in catalysts prepared by impregnation. The importance of the surface of the carrier was investigated by carrying out experiments with Mg(OH)2 having different specific surface areas. Some solids were found to have micropores which were not available for the reaction. The activity was found to increase with the increase of the external surface area rather than with the total area. A mechanism is suggested based on the continuous formation of an unstable manganese peroxy-complexes which break on the surface of magnesium hydroxide and undergo a cycle of oxidation and reduction resulting in the decomposition of H2O2 into O2 and H2O.