Synergistic Reduction Mechanism of NO<sub><i>x</i></sub> by NH<sub>3</sub> and CO Catalyzed by Mn–Co Oxides and the Oxidation Process of CO: In Situ DRIFTS and DFT Study
Shiwang Han, Chengbo Xuan, Luyuan Wang, Xingyu Zhang, Ranlei Shao, Xingxing Cheng, Zhiqiang Wang
Abstract
In this study, Mn–Co bimetallic catalysts were prepared by a coprecipitation method. The effect of different Mn/Co molar ratios on the performance of NH 3 –SCR, CO-SCR, and CO oxidation was investigated, and a representative catalyst was selected to test the NO x catalytic activity of the NH 3 –CO-SCR synergy reaction. The microphysical and chemical properties of the samples were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, and other analytical techniques. The CO-assisted NH 3 removal mechanism of NO x was explored through in situ diffuse reflectance infrared spectroscopy (DRIFTS) and density functional theory (DFT). The results show that MC-3 has the best NO x catalytic activity and a wider SCR reaction temperature window. In the synergy reaction, the NO x conversion rate of NH 3 –SCR can be reached at NH 3 = 400 ppm, and the N 2 selectivity is effectively improved. In situ DRIFTS and DFT results show that NH 3 –SCR follows the L-H mechanism. In the presence of CO, some CO competes with NH 3 for adsorption on the Mn sites, which suppresses the adsorption activation of NH 3 and reduces the CO oxidation activity. Second, with CO participation, the activation energy required for NH 4 NO 3 * to form is lower, which promotes its further decomposition into N 2 and H 2 O, and is of great significance for CO-assisted NH 3 removal of NO x technology.