A Density Functional Theory Study of NH 3 and NO Adsorption on the β-MnO 2 (110) Surface

Abstract

The adsorption of NH₃ and NO on the β-MnO₂ (1 1 0) surface has been investigated by density functional theory using periodic models. The energetically favourable sites of adsorption of the gases on the β-MnO₂ surface are 4-fold coordinate Mn (Mn4-top) and 5-fold coordinate Mn (Mn5-top). The relative adsorption energies (E_ads) of these gases on the Mn4-top site and Mn5-top site are in the orders NH₃ (E_ads = −1.02 eV) > NO (E_ads = −0.96 eV) and NH₃ (E_ads = −0.63 eV) > NO (E_ads = −0.49 eV). The N-H and N–O bond lengths, Mulliken charges and the densities of states of the NH₃ and NO molecules are discussed after adsorption. The calculated results indicate that the coordination number of surface Mn ions has a significant influence on the adsorption capacity. Furthermore, the analysis of the results of the density of states determinations shows that when NH₃ and NO are adsorbed with the NH₃-Mn and NO-Mn configurations, the bonding mechanism is mainly from the interaction between the NH₃ or NO molecule and the Mn d orbital, which is the major reason for the strong chemical adsorption of NH₃ and NO.