The oxidative abstraction of hydrogen from adsorbed ammonia is the first step in selective catalytic reduction (SCR) and NH3 adsorptions on the MnO, surfaces played a significant role in the mechanism of SCR with NH3. NH3 adsorptions on the Mn203 (2 2 2), Mn304 (2 1 1) and Mn02 (1 1 0) surfaces were investigated by the density functional theory (DFT) method. With more negative adsorption energy values, the Mn203 (2 2 2) and Mn304 (2 1 1) surfaces tended to be the favorable adsorption sites for NH3 molecule. In addition, the shorter Mn N bonds indicated that NH3 adsorptions took place easily on Mn203 (2 2 2) and Mn304 (2 1 1) surfaces. According to the ammonia temperature programmed desorption (NH3-TPD) performance, Mn203 and Mn304 showed significantly higher amount of desorbed NH3, which was in good agreement with the DFT study. Meanwhile, the NH3-SCR performances of Mn203 and Mn304 for NO conversion below 433 K show higher performance than that of Mn02. Crown Copyright 2013 Published by Elsevier B.V. All rights reserved.