Catalytic decomposition of H2O2 over manganese oxides supported on an active alumina

A series of manganese oxides loaded on to an active alumina support was prepared by impregnation methods and the resulting samples preheated in air at 400degreesC, 650degreesC or 900degreesC for 6 h, The amount of manganese, expressed as Mn2O3, was varied between 3.7 wt\% and 55.3 wt\%. The kinetics of the decomposition of H2O2 in an aqueous medium were studied in the presence of these oxides. The catalytic activities increased initially as the amounts of manganese present increased, attaining a maximum value at 13.4 wt\% Mn2O3 and then decreasing on increasing both the amount of manganese above this limit and the precalcination temperature from 400degreesC to 900degreesC. The specific surface areas of the various catalysts were determined by BET analysis of the nitrogen adsorption isotherms. The S-BET values varied from 244 m(2)/g to 80 m(2)/g both as a function of the extent of loading and the precalcination temperature, However, the activation energy for sintering, DeltaE(S) increased on increasing the amount of Mn2O3 present. The apparent activation energy for H2O2 decomposition conducted over the various solids was found to be virtually unaffected by a change in the amount of manganese present.