Modulation of Electron-Donation Ability to Enhance the Low-Temperature NO Oxidation Performance of Mn<sub>3</sub>O<sub>4</sub>/YMn<sub>2</sub>O<sub>5</sub>
Rui Chen, Zihao Xu, Bowen Wang, Ziteng Mao, Zheng Zhao, Yongke Hou, Meisheng Cui, Yongqi Zhang, Weidong Zhuang, Juanyu Yang, Xiaowei Huang
Abstract
Managing the substantial NO x emissions during the cold start of diesel vehicles presents a critical environmental challenge. Enhancing the conversion of NO to NO 2 at low temperatures can significantly improve the efficiency of diesel aftertreatment systems. Manganese-based mullite catalysts are cost-effective and promising for NO oxidation; however, their low-temperature activity requires further enhancement. In this study, we innovatively leverage the strong electronic interactions between Mn 3 O 4 and YMn 2 O 5 to enhance the low-temperature NO oxidation activity (50% at 200 °C) of Mn 3 O 4 /YMn 2 O 5, demonstrating high activity (CO conversion: T 100 = 222 °C, C 3 H 6 conversion: T 100 = 209 °C, C 3 H 8 conversion: T 100 = 341 °C, NO maximum conversion: 78.7% at 300 °C) and stability (CO and C 3 H 6 conversion: 100%, C 3 H 8 conversion: 94.06%, NO conversion: 78.7% at 300 °C for 10 h) under a simulated exhaust gas mixture. Structural analysis (X-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM)) confirmed the uniform coexistence of Mn 3 O 4 and YMn 2 O 5 phases. Furthermore, X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) indicated that Mn 3 O 4 decreased the average Mn valence state, increased Mn–Mn interactions, and modified Mn–O coordination, contributing to improved catalytic performance. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations further revealed that Mn 3 O 4 /YMn 2 O 5 enhances electron transfer to adsorbed O 2, reducing its dissociation energy barrier and destabilizing nitrite intermediates, thereby accelerating the Eley–Rideal (E–R) mechanism for NO oxidation.