Simultaneous Removal of Soot and NO<i><sub>x</sub></i> from Diesel Engines over Three-Dimensionally Ordered Macroporous ZSM-5-Supported MMnO<sub>δ</sub> Catalysts
Lanyi Wang, Di Yu, Zhen Zhao, Xuehua Yu, Dong Li, Shengran Zhou, Chengming Zhong, Jia Hou, Chengyang Yin, Xiaoqiang Fan
Abstract
Three-dimensionally ordered macroporous (3DOM) ZSM-5 support was successfully designed and synthesized via a combination of seed- and steam-assisted methods. In addition, MMnO δ /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 PrMnO δ 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 Mn 4+ and O II /O I ratio compared with the other MMnO δ /3DOM ZSM-5 catalysts. Meanwhile, the high turnover frequency and low E a over 3DOM ZSM-5-supported PrMnO δ 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 NO 2 -assisted mechanisms.