Decomposition of Hydrogen Peroxide on MnO2/TiO2 Catalysts

Catalysts containing 2-10 wt% MnO 2 supported on TiO 2 were examined for H 2 O 2 decomposition. Catalysts were prepared by impregnation of a high TiO 2 surface area. X-ray defraction patterns, scanning electron micrographs, and surface area measurements gave evidence of a uniform distribution of the active phase on the support surface and of the absence of segregated manganese oxides phases. Temperature programmed reduction measurements showed the presence, beside MnO 2 , of different Mn oxides species formed by interaction between the active phase and the support surface. The MnO 2 reducibility increased, whereas the mean oxidation state of manganese decreased with increasing manganese content. Catalytic tests were performed in a batch reactor with 50 or 70% concentration H 2 O 2 solutions. Catalytic activity was very high at the beginning of the tests and decreased with time, reaching a final constant value that increased with manganese content. Kinetic constants, evaluated assuming a first-order reaction rate, were comparable or higher than those of similar manganese-based catalysts. An optimal MnO 2 content was found, corresponding to the quite complete surface monolayer coverage. A reaction mechanism involving an Mn 4 + -Mn 3 + redox couple has been proposed.