A density functional theory study of formaldehyde adsorption on ceria

Molecular adsorption of formaldehyde on the stoichiometric CeO2(1 1 1) and CeO2(1 1 0) surfaces was studied using periodic density functional theory. Two adsorption modes (strong chemisorbed and weak physisorbed) were identified on both surfaces. This is consistent with recent experimental observations. On the (1 1 1) surface, formaldehyde strongly chemisorbs with an adsorption energy of 0.86 eV to form a dioxymethylene-like structure, in which a surface O lifts from the surface to bind with the C of formaldehyde. A weak physisorbed state with adsorption energy of 0.28 eV was found with the O of formaldehyde interacting with a surface Ce. On the (1 1 0) surface, dioxymethyelene formation was also observed, with an adsorption energy of 1.31 eV. The weakly adsorbed state of formaldehyde on the (1 1 0) surface was energetically comparable to the weak adsorption state on the (1 1 1) surface. Analysis of the local density of states and charge density differences after adsorption shows that strong covalent bonding occurs between the C of formaldehyde and surface O when dioxymethylene forms. Calculated vibrational frequencies also confirm dioxymethylene formation. Our results show that as the coverage increases, the adsorption of formaldehyde on the (1 1 1) surface becomes weak, but is nearly unaffected on the (1 1 0) surface.