NO adsorption and oxidation on Mn-doped CeO2 (111) surfaces: A DFT+U study

Abstract

The adsorption of NO molecules on Mn-doped CeO2 (111) surfaces for NO oxidation has been studied by employing the periodic density functional theory plus U (DFT+U) method. Through our calculations, it is demonstrated how Mn-doped CeO2 with superior NO oxidation activity benefits from the high mobility of the oxygen near the Mn cations. On unreduced Mn-doped CeO2 (111) surfaces, the NO molecule preferentially interacted with the first neighboring O of the Mn cation, with the N also bonding to an Mn cation (Eads = –3.30 eV) or Ce cation (Eads = –2.90 eV). When NO adsorbs on the surface of defective Mn-doped CeO2 with O2 adsorbed in advance, an ONOO* four atoms species is formed on the surface (Eads = –2.51 eV and –2.02 eV), which is an intermediate and can decompose into NO2, NO2* and O*. The adsorption structure with higher adsorption energy has a closer geometry to NO2, indicating a deeper oxidation of NO. The calculation results indicate that the presence of Mn only has a strong effect on the nearby oxygen atoms and that the Mn-doped CeO2 surface has similar properties to a noble metal in NO oxidation catalysis. In DOS plots, the spin of the electron state of the adsorption structures involving the oxidation of NO is symmetric, indicating that electron transfer occurs from the slab to NO and strong covalent bonds are formed between N and O on the slab, which can also be confirmed by the charge density difference plots.