Synergistic Reduction Mechanism of NO_<i>x</i> by NH₃ and CO Catalyzed by Mn–Co Oxides and the Oxidation Process of CO: In Situ DRIFTS and DFT Study

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 NH3–SCR, CO-SCR, and CO oxidation was investigated, and a representative catalyst was selected to test the NOx catalytic activity of the NH3–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 NH3 removal mechanism of NOx was explored through in situ diffuse reflectance infrared spectroscopy (DRIFTS) and density functional theory (DFT). The results show that MC-3 has the best NOx catalytic activity and a wider SCR reaction temperature window. In the synergy reaction, the NOx conversion rate of NH3–SCR can be reached at NH3 = 400 ppm, and the N2 selectivity is effectively improved. In situ DRIFTS and DFT results show that NH3–SCR follows the L-H mechanism. In the presence of CO, some CO competes with NH3 for adsorption on the Mn sites, which suppresses the adsorption activation of NH3 and reduces the CO oxidation activity. Second, with CO participation, the activation energy required for NH4NO3* to form is lower, which promotes its further decomposition into N2 and H2O, and is of great significance for CO-assisted NH3 removal of NOx technology.