Oxidation of SO2 catalysed by Mn-zeolites in aqueous phase

Mn2+ was heterogenised over six different zeolites by ion exchange and their activity for SO2 oxidation was studied by conductimetry. The activity of the heterogenised Mn2+ was compared with both, Mn2+ as a homogeneous catalyst and with a more conventional carbon based catalyst. Mn2+ was shown to be the only active phase, consequently the catalysts containing the higher content of ion exchanged Mn2+, were the most active ones. Additionally, the influence of the hydrophilia and the structure of the different zeolites used on the activity of the heterogenised Mn2+ were also analysed. Both the hydrophilia and the structure of the zeolites, which favour the interaction of the reaction intermediates and the Mn2+, were found to be the key parameters for the SO2 oxidation activity of the catalysts. The combination of hydrophilia, a high Mn2+ ion exchange capacity, and a well-defined microporous structure, allows that almost all the zeolites studied present higher activity for aqueous phase SO2 oxidation, than the homogeneous catalyst and significantly higher than the conventional carbon based catalyst for this reaction.