Raspberry-like shape MnOx/Cu-SSZ-13 catalysts: Facile preparation, catalytic performance and reaction mechanism for the simultaneous removal of soot and NOx

Abstract

n%MnOx/Cu-SSZ-13 catalysts with raspberry-like shapes were synthesized using the steam-assisted method and incipient impregnation methods. The catalytic activities of as-prepared catalysts were also tested for the simultaneous removal of soot and nitrogen oxides (NOx), and the 40 %MnOx/Cu-SSZ-13 catalyst exhibited the best catalytic performance with the lowest T_m temperature (455 °C) for soot combustion, the widest temperature window (144–417 °C) for NO conversion (>90 %), and the highest N₂ selectivity (96 %). The obtained catalyst achieves the efficient elimination of NOx and soot in the temperature range of diesel vehicle exhaust emissions because of its rich active oxygen species, sufficient acidic sites, excellent redox properties, high proportion of surface Mn⁴⁺, and unique raspberry-like structure. Moreover, the active sites involved in the removal of soot and NOx and reaction mechanism were also elucidated according to the results of density functional theory (DFT) calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTs). The results shows that Mn₂O₃ is the active phase for soot oxidation, while Cu-SSZ-13 is the best choice of active phase for NH₃ selective catalytic reduction (NH₃-SCR). And the existence of Mn₂O₃ promotes the reduction of NO on Cu-SSZ-13. Additionally, the 40 %MnOx/Cu-SSZ-13 catalyst followed the E-R mechanism in NH₃-SCR at low temperatures as well as NO₂-assisted mechanism and the active oxygen mechanism in soot combustion at high temperatures.