Revealing the crystal facet effect on NO formation during the NH-SCR over α-MnO catalysts.

The detailed atomic-level mechanism of the effect induced by engineering the crystal facet of α-MnO catalysts on NO formation during ammonia-selective catalytic reduction (NH-SCR) was ascertained by combining density functional theory (DFT) calculations and thermodynamics/kinetic analysis. The surface energies of α-MnO with specific (100), (110), and (310) exposed planes were calculated, and the adsorptions of NH, NO, and O on three surfaces were analyzed. The adsorption energies showed that NH and NO molecules could be strongly adsorbed on the surface of the α-MnO catalyst, while the adsorption of O was weak. Moreover, the key steps in the oxidative dehydrogenation of NH and the formation of NHNO as well as dissociation of NH were studied to evaluate the catalytic ability of NH-SCR reaction and N selectivity. The results revealed that the α-MnO catalyst exposed with the (310) plane exhibited the best NH-SCR catalytic performance and highest N selectivity, mainly due to its low energy barriers in NH dehydrogenation and NHNO generation, and difficulty in NH dissociation. This study deepens the comprehension of the facet-engineering of α-MnO on inhibiting NO formation during the NH-SCR, and points out a strategy to improve their catalytic ability and N selectivity for the low-temperature NH-SCR process.