Simultaneous Removal of Soot and NOx from Diesel Engines over Three-Dimensionally Ordered Macroporous ZSM-5-Supported MMnOδ Catalysts

Three-dimensionally ordered macroporous (3DOM) ZSM-5 support was successfully designed and synthesized via a combination of seed- and steam-assisted methods. In addition, MMnOδ/3DOM ZSM-5 (M = Fe, Co, Ce, Pr, and W) catalysts were prepared using ZSM-5 as a carrier and showed good catalytic performance, which may be due to the catalysts' unique pore structures and interactions between M and Mn. 3DOM ZSM-5-supported PrMnOδ possesses the best reaction performance for soot oxidation, with a lowest peak temperature of 430 °C, and the best low-temperature denitration performance, with a temperature window of 149–336 °C when NO conversion is 80%. This may be due to the catalyst's better redox performance, abundant active oxygen and acidic sites, and the higher content of Mn4+ and OII/OI ratio compared with the other MMnOδ/3DOM ZSM-5 catalysts. Meanwhile, the high turnover frequency and low Ea over 3DOM ZSM-5-supported PrMnOδ also contributed to its high intrinsic activity. The corresponding reaction mechanisms were proposed according to in situ diffuse reflectance infrared Fourier transform spectroscopy analysis and other characterizations. At low temperature (<300 °C), the selective catalytic reduction reaction follows the Eley–Rideal and Langmuir–Hinshelwood mechanisms. At a high temperature, the mechanisms for soot combustion include active oxygen oxidation and NO2-assisted mechanisms.