Insights into the selective catalytic reduction of NO by NH3 over Mn3O4(110): a DFT study coupled with microkinetic analysis

Abstract

Nitric oxide (NO x ), as one of the main pollutants, can contribute to a series of environmental problems, and to date the selective catalytic reduction (SCR) of NO x with NH3 in the presence of excess of O2 over the catalysts has served as one of the most effective methods, in which Mn-based catalysts have been widely studied owing to their excellent low-temperature activity toward NH3-SCR. However, the related structure-activity relation was not satisfactorily explored at the atomic level. By virtue of DFT+U calculations together with microkinetic analysis, we systemically investigate the selective catalytic reduction process of NO with NH3 over Mn3O4(110), and identify the crucial thermodynamic and kinetic factors that limit the catalytic activity and selectivity. It is found that NH3 prefers to adsorb on the Lewis acid site and then dehydrogenates into NH2* assisted by either the two- or three-fold lattice oxygen; NH2* would then react with the gaseous NO to form an important intermediate NH2NO that prefers to convert into N2O rather than N2 after the sequential dehydrogenation, while the residual H atoms interact with O2 and left the surface in the form of H2O. The rate-determining step is proposed to be the coupling reaction between NH2* and gaseous NO. Regarding the complex surface structure of Mn3O4(110), the main active sites are quantitatively revealed to be O3c and Mn4c.