Synthesis and characterization of manganese oxides employed in VOCs abatement

Abstract

Two MnO2 were prepared by different methods: (i) MnCO 3 decomposition; and (ii) oxidation of acid MnSO4 solution. The combined use of X-ray diffraction (XRD), DRIFTS, DRS-UV-vis and TGA techniques revealed: (i) the presence of Mn4+-Mn3+; (ii) a poor crystallinity; and (iii) OH species at temperatures higher than 200°C. The catalysts were tested in the complete oxidation of ethanol to carbon dioxide and water, and the reaction results showed that the catalytic activity of both samples were larger than MnO2 (pyrolusite, β-MnO2) and Mn2O3 (like bixbyite) oxides. The high activity of the prepared oxides can be related to the simultaneous presence of Mn3+ and Mn4+ ions and OH- species generated by Mn4+ vacancies. In addition, in situ DRIFT spectroscopy demonstrated a different mechanism of adsorption-reaction of ethanol between the two synthesized manganese oxides.