Density Functional Theory plus U Study of Methanol Adsorption and Decomposition on CuO Surfaces with Oxygen Vacancy

Abstract

The adsorption and decomposition of methanol (CH3OH) and methoxy radical (CH3O) on CuO(111) were investigated via density functional theory calculations with a Hubbard U correction. The configurations and electronic structures of CH3OH and CH3O adsorbed on CuO(111) surfaces were analyzed. CH3OH molecules were preferentially adsorbed on Cu top sites with OMeOH atoms and H-O3C bonds formed simultaneously. Adsorption on Cu3C sites was more stable than on Cu4C sites, with higher binding energy and shorter Cu-OMeOH and H-OCuO bonds. Stable configurations were also achieved with OMeOH-H bond scission, which were only found on Cu3C and O3C sites. On surfaces with oxygen vacancies, adsorption configurations did not change a lot, while there was increased adsorption energy with shorter bond lengths of Cu-OMeOH and H-OCuO and longer bond lengths of H-OMeOH, indicating the formation of oxygen vacancies enhanced the CH3OH adsorption and H-OMeOH bond scission, and thus accelerated CH3OH decomposition. The dissociative adsorption configuration MeOH-ov3C5 had the highest adsorption energy, at –0.71 eV, with the H-OCuO bond length at 1.00 Å and H-OMeOH at 1.70 Å. Compared with CH3OH, the adsorption energy of CH3O was much higher and reached –1.52 eV in MeO-3C2. The Cu-OMeO and C-OMeO bond distances were 1.80 Å and 1.40 Å, respectively, which were both shorter than CH3OH adsorption. The formation of oxygen vacancies significantly enhanced CH3O adsorption, as CH3O moved to a vacancy and bound with three Cu atoms by OMeO, whose adsorption energy increased to –3.19 eV. Other configurations had OMeO binding with two Cu3C atoms and formed a bridging bond, with adsorption energies of –2.53 and –2.61 eV.