Catalytic Decomposition of H 2 O 2 over Manganese Oxides Supported on an Active Alumina

Abstract

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 400°C, 650°C or 900°C 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 400°C to 900°C. 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 m²/g to 80 m²/g both as a function of the extent of loading and the precalcination temperature. However, the activation energy for sintering, ΔE_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.