Synthesis and catalytic activity of manganese dioxide (type OMS-2) for the abatement of oxygenated VOCs

Two solids were synthesized by the reaction between Mn2+ and KMnO4 in different order. The results of the characterization of both solids showed that: (i) they are poorly crystalline, although both belong to the Cryptomelane (OMS-2) phase; (ii) these materials are mesoporous (mesopores concentration in the order of 80%); (iii) they contain the couple Mn3+/Mn4+, being the Mn3+ concentration a function of the preparation method. Both catalysts were analyzed in the total oxidation of ethanol and the percentage of ethanol conversion on both solids reached 50% at 155 °C. The adsorption studies of methanol and ethanol have demonstrated the presence of basic sites and two different adsorption sites. The analysis of the results suggest that the amount of adsorbed ethanol molecules and the lowest temperature of CO2 desorption detected is due to the Mn3+ concentration. This phenomenon is ascribed to a high concentration of Mn3+ which could originate a weak Mn–O bond and the formation of more active oxygen species which would improve the catalytic performance.