Silica and silica–titania intercalated MCM-36 modified with iron as catalysts for selective reduction of nitrogen oxides – the role of associated reactions

Abstract

The MCM-22 zeolite and its silica and silica–titania intercalated forms, MCM-36 and xTi-MCM-36, were synthesized and then modified with iron by the ion-exchange method. The zeolitic samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD, FTIR, RS, UV-vis DRS), texture (N₂-sorption), surface acidity (NH₃-TPD) and reducibility (H₂-TPR). Fe-Modified zeolites were found to be active and selective catalysts for the NH₃-SCR process, effectively operating to about 475 °C. The activity of the studied catalysts increased with an increase in titanium content in the interlayer pillars of MCM-36. Apart from the NH₃-SCR process, other associated reactions – NO to NO₂ oxidation, ammonia oxidation and N₂O decomposition – that may influence the overall efficiency of nitrogen oxide reduction were also analysed and discussed.