Experimental Study on SO_2-to-SO_3 Conversion Over Fe-Modified Mn/ZSM-5 Catalysts During the Catalytic Reduction of NO_X

摘要

Mn-Fe/ZSM-5 catalysts with different Fe loading amounts were prepared using wet impregnation and the effects of these catalysts on SO3 formation during the catalytic reduction of NOx were assessed. Variations in the catalysts' physicochemical properties with different Fe contents were also investigated using BET, XRD, SEM-EDS, FT-IR, H-2-TPR and XPS techniques. The 9Mn9Fe catalyst gave the highest SO2-to-SO3 and NOx conversions, and adding Fe also improved the catalyst's SO2 resistance. The presence of NO2 caused the formation of nitrate ions on the catalyst surface during fast SCR. These nitrate ions re-oxidized the active sites more rapidly than O-2 at low temperatures, thereby promoting the redox reaction. BET, XRD and SEM-EDS showed that optimal Fe loading amount reduced MnOx crystallinity while improving surface dispersion. Adding excessive Fe caused the active compositions to accumulate on the catalyst surface. FT-IR, H-2-TPR and XPS demonstrated that optimal Fe loading amount increased the quantity of Mn4+=O bonds while raising the concentrations of Mn4+ ions and lattice oxygen, thus enhancing SO2-to-SO3-conversion. Therefore, although suitable amounts of Fe and NO2 promoted NOx conversion, these species also significantly increased SO2-to-SO3 conversion.