A DFT study of the mechanism of NH3-SCR NOx reduction over Mn-doped and Mn–Ti co-doped CoAl2O4 catalysts

Abstract

The catalytic performance of cobalt–chromium spinel NH₃-SCR can be enhanced by Mn-doped and Mn–Ti co-doped catalysts; however, there is insufficient understanding of the underlying reaction mechanism. Our work is based on a first-principles computational approach of density functional theory to calculate the optimized configurations of CoAl₂O₄(100) both before as well as after being Mn-doped and Mn–Ti co-doped. We also simulated the adsorption behavior of gas molecules such as NH₃ and NO on the catalyst before and after doping. The optimized configurations and the associated energy distributions for the NH₃ dehydrogenation and SCR reactions on Mn_0.1Co_0.9Al₂O₄ and Mn_0.1Co_0.9Ti_0.1Al_1.9O₄ catalysts have undergone a thorough investigation. Our findings demonstrate that the introduction of Mn-doping and Mn–Ti co-doping can enhance the adsorption capacity of gas molecules, such as NH₃ and NO, on CoAl₂O₄ catalysts while significantly reducing the energy barriers for NH₃ dehydrogenation and SCR reactions. The performance of Mn–Ti co-doping surpasses that of Mn-doping. Furthermore, we conducted an investigation into the adsorption of H₂O and SO₂ on the doped catalysts, revealing that Mn–Ti co-doping effectively enhances the water and sulfur resistance properties of the catalysts. Our study is anticipated to serve as a crucial theoretical guide for the development, preparation, and modification of cobalt–aluminum spinel catalysts.