Insight into the activity and SO2 tolerance of hierarchically ordered MnFe1-δCoδOx ternary oxides for low-temperature selective catalytic reduction of NOx with NH3

Abstract Manganese (Mn)-based mixed oxides are considered the most efficient catalysts for low-temperature ammonia selective catalytic reduction of nitrogen oxides (NOx) (NH3-SCR of NOx). Water resistance and sulfur tolerance, especially the SO2 tolerance of Mn-based catalysts, are the main obstacles preventing their practical application. Therefore, in this study, a series of cobalt (Co)-doped MnFeOx ternary mixed oxides catalysts with a hierarchically ordered structure (Hierc-MnFe1-δCoδOx, δ = 0.2, 0.4 and 0.6) were developed and applied for NH3-SCR of NOx at low temperature. Compared with Hierc-MnFeOx, Hierc-MnFe1-δCoδOx catalyst exhibited enhanced low-temperature activity and a broadened temperature window (NOx conversion above 80% was between 90 and 343 °C over Hierc-MnFe0.6Co0.4Ox), as well as better H2O resistance and SO2 tolerance. The enhanced low-temperature activity was attributed to a larger amount of active oxygen species, a higher proportion of Mn4+, Fe3+ and Co3+ content, and the improvement of surface acidity, which can facilitate the adsorption and activation of NO and NH3. Additionally, the Hierc-MnFe0.6Co0.4Ox catalyst exhibited superior soot tolerance due to its special hierarchically ordered architecture. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that the Co-modified Hierc-MnFe1-δCoδOx ternary oxide catalyst could efficiently protect nitrate species on Hierc-MnFe0.6Co0.4Ox from the poisoning effect of SO2, thereby boosting its SO2 tolerance. This study provides a good candidate for low-temperature deNOx application with enhanced SO2 and soot tolerance.