First principles and experimental study of NH3 adsorptions on MnOx surface

Abstract

The oxidative abstraction of hydrogen from adsorbed ammonia is the first step in selective catalytic reduction (SCR) and NH3 adsorptions on the MnOx surfaces played a significant role in the mechanism of SCR with NH3. NH3 adsorptions on the Mn2O3 (222), Mn3O4 (211) and MnO2 (110) surfaces were investigated by the density functional theory (DFT) method. With more negative adsorption energy values, the Mn2O3 (222) and Mn3O4 (211) surfaces tended to be the favorable adsorption sites for NH3 molecule. In addition, the shorter MnN bonds indicated that NH3 adsorptions took place easily on Mn2O3 (222) and Mn3O4 (211) surfaces. According to the ammonia temperature programmed desorption (NH3-TPD) performance, Mn2O3 and Mn3O4 showed significantly higher amount of desorbed NH3, which was in good agreement with the DFT study. Meanwhile, the NH3-SCR performances of Mn2O3 and Mn3O4 for NO conversion below 433K show higher performance than that of MnO2.