Modified cold-rolled sludge as catalyst for selective catalytic reduction of NOx with NH3 at low temperatures

Iron-based mixed oxides are considered commercially promising environmentally friendly catalysts for selective catalytic reduction with NH3 (NH3-SCR) for removing nitrogen oxides (NOx) because of their high catalytic activity. In this work, cold-rolled sludge with high content of iron species was used as the iron precursor for preparing catalysts by supported MnOx and/or sulfuric acid modifications. The prepared catalyst showed 100 % of NOx conversion in the temperature range of 60-180 celcius and exhibited good resistance to SO2 and H2O. This is mainly attributed to the synergy between MnOx and iron sulfate, which improved the denitration performance at super low-temperature by improving the textural properties, redox capacity, surface acidity, and surface chemical states of the catalyst. Furthermore, the presence of Fe3+ and SO4 2- protected the active ingredient from the poisoning of SO2 and improved its sulfur resistance. The super low-temperature reaction mechanism of the catalyst was unraveled by transient reaction experiments and In situ DRIFTS. The results show that both Bronsted and Lewis acid sites are present in 10 %Mn/CRS-S-400, and that the reaction is dominated by the Langmuir-Hinshelwood (L-H) mechanism. This study provides an innovative and cost-effective strategy for the design of NH3-SCR catalysts by sulfation iron-based mixed oxides.