Density functional theory study of water interactions on Mn-doped CeO2(1 1 1) surface

Abstract

Spin-polarized density functional theory (DFT + U) periodic calculations have been performed to study water adsorption and dissociation on the 12.5% Mn-doped CeO2(1 1 1) surface. Our results indicated that Mn cation is the surface active site for water adsorption and dissociation reactions. The H2O molecule preferably adsorbs on a Mn cation, causing some relaxation of the surface O-layer and, thus, facilitating the bonding of one of the HH2O with the nearest oxygen atom. After overcoming an energy barrier of 0.46 eV, the water molecule could dissociate into OH and H species. The latter configuration is about 50% more exothermic than the molecular one, suggesting the Ce0.875Mn0.125O1.9375(1 1 1) surface would be easily hydroxylated under reaction conditions. In addition, the calculations showed that water adsorption on the Mn-doped CeO2(1 1 1) surface did not favor the creation of surface oxygen vacancies as it has been reported for pure CeO2(1 1 1). On the other hand, we created a surface oxygen defect in the slab with structural oxygen vacancies and computed water interactions on the reduced surface. Although, the adsorption of OH species in the O-hole caused many surface and subsurface atomic displacements, no changes in the oxidation state of Mn and Ce cations were detected.