DFT Analysis of the Reaction Mechanism for NH3-SCR of NOx over Mn/γ-Al2O3 Catalyst

The SCR reaction mechanism on the Mn/gamma-Al2O3 catalyst was studied using density functional theory. The intermediates, energy barriers, and rate-determining steps of N-2, NO2, and N2O formation were calculated. It was found that NH3 could be adsorbed on the Lewis acid sites and participated in the SCR reaction in the form of coordinated NH3. In addition, NH3 could also be adsorbed on the Bronsted acid sites and participated in the SCR reaction in the form of NH4+. The rate-determining steps of these two pathways were H2O* desorption and NH4NO2* decomposition. The energy barriers were 111.85 and 455.89 kJ/mol, respectively, indicating that NH3 mainly participated in the N-2 formation reaction in the form of coordinated NH3. The active oxygen formed by the decomposition of adsorbed O-2 could oxidize gaseous NO into NO2. NO could also be oxidized by the lattice oxygen while the energy barrier via this pathway was 10.30 kJ/mol higher, indicating that the active oxygen was more reactive. The energy barriers of N2O formation via three pathways, NO decomposition, deep dehydrogenation of NH3, and two-step dehydrogenation of NH2NO, were 471.62, 281.25, and 341.55 kJ/mol, respectively, impling that N2O formation was mainly caused by the deep dehydrogenation of NH3.