Influencing mechanism of alkali metals on the adsorption property of NH3, NO, O2 and dehydrogenation reaction of NH3 on the β-MnO2 (1 1 0) surface: A DFT + U study

To explain the reaction mechanism of Mn-based catalysts at atomic level and vital activity-limiting factors during the deNOx progress after K and Na poisoning, a detailed computational investigation on the surface of β-MnO2 (1 1 0) was performed by first-principles computation coupled with microkinetic analysis. NH3, NO, and O2 can be steadily absorbed on the β-MnO2 (1 1 0) surface. After K or Na poisoning, the adsorption of NH3 is inhibited, which leads to significantly decreasing the β-MnO2 activity. However, K or Na slightly enhances the adsorption of NO, which is the reason that the deNOx performance of the β-MnO2 catalyst is enhanced in some situations. K or Na severely inhibits the process of NH3 dehydrogenation while promoting the reaction of *OH+*OH → H2O +*H. The promoting or inhibiting effect of K is stronger than that of Na. The number of *OH groups on the β-MnO2 (1 1 0) surface is greatly reduced due to the inhibitory effect of K or Na on the adsorption and dehydrogenation of NH3, so the generation of H2O is limited, thereby inhibiting the overall NH3-SCR reaction. These conclusions can provide consolidated theoretical support for understanding the inactivation mechanism of alkali metals and obtaining more efficient Mn-based catalysts.