Metal-Doped Mesoporous MnO[sub.2]-CeO[sub.2] Catalysts for Low-Temperature Pre-Oxidation of NO to NO[sub.2] in Fast SCR Process

• Published in: Catalysts 2023-04, Vol.13 (4)
• Main Authors: Kuo, Chun-Nan, Li, Cheng-Shiuan, Lai, Yu-Lun, Yen, Shao-I
• Format: Article
• Language: English
• Subjects: Automotive emissions; Catalysts; Oxidation-reduction reaction
• ISSN: 2073-4344; 2073-4344
• DOI: 10.3390/catal13040694

Selective catalytic reduction (SCR) is an effective system for treating nitrogen oxides (NO[sub.x]; mainly NO), and fast SCR requires the equimolar reactants of NO and NO[sub.2]. This study focused on catalysts for oxidizing 50% of NO to NO[sub.2]. A series of catalysts composed of a variety of components, such as mesoporous mMnO[sub.2]-nCeO[sub.2] as carrier catalysts (m:n = 9:1 and 7:3) and transition metals (e.g., Fe, Co, Ni, Cu, and Cr), were synthesized and characterized using N[sub.2] adsorption, in situ XRD, TEM, and XPS. All samples had a mesoporous structure with pore size around 8 nm. XPS results demonstrated that addition of cerium ion increased the surface area and provided oxygen vacancy due to the formation of Ce[sup.3+] within the structure. NO oxidation activity was tested using a feed (205~300 ppm NO and 6% O[sub.2]) that simulated typical flue gas conditions. Doped mesoporous mMnO[sub.2]-nCeO[sub.2] has higher NO oxidation activity than pristine mMnO[sub.2]-nCeO[sub.2]. The doped mMnO[sub.2]-nCeO[sub.2] catalyzed 50% of NO to NO[sub.2] at between 140 and 200 °C resulting in an equivalent amount of NO and NO[sub.2]. Among the transition metals, Cu, Ni, Co, Fe, and Cr have the highest to lowest oxidation activity, respectively. The precatalytic oxidation of NO can potentially be combined with the current SCR system without changes to existing equipment and can be applied to the exhaust gas treatment for de-NO[sub.x].