Methanol Adsorption on the Clean CeO₂(111) Surface:  A Density Functional Theory Study

Molecular and dissociative adsorption of methanol at various sites on the stoichiometric CeO₂(111) surface have been studied using density functional theory periodic calculations. At 0.25 monolayer (ML) coverage, the dissociative adsorption with an adsorption energy of 0.55 eV is slightly favored. The most stable state is the dissociative adsorption of methanol via C−H bond breaking, forming a coadsorbed hydroxymethyl group and hydrogen adatom on two separate O_3C surface sites. The strongest molecular adsorption occurs through an O−Ce_7C connection with an adsorption energy of 0.48 eV. At methanol coverage of 0.5 ML, the dissociative adsorption and the molecular adsorption became competitive. The adsorption energy per methanol molecule for both adsorption modes falls into a narrow range of 0.46−0.55 eV. As methanol coverage increases beyond 0.5 ML, the molecular adsorption becomes more energetically favorable than the dissociative adsorption because of the attractive hydrogen bonding between coadsorbed methanol molecules. At full monolayer, the adsorption energy of molecular adsorption is 0.40 eV per molecule while the adsorption energy for total dissociative adsorption of methanol is only 0.17 eV. The results at different methanol coverages indicate that methanol can adsorb on a defect-free CeO₂(111) surface, which are also consistent with experimental observations.