A study was made of the effect of gold doping on oxygen vacancy formation and

CO adsorption on the (110) and (100) surfaces of ceria by using density functional

theory, corrected for on-site Coulomb interactions (DFT+U). The Au dopant

substitutes a Ce atom in the surface layer, leading to strong structural distortions.

The formation of one oxygen vacancy near a dopant atom was energetically

“downhill” while the formation of a second vacancy around the same dopant

requires energy. When the surface was in equilibrium with gaseous oxygen at 1atm

and room temperature there was a 0.4 probability that no oxygen atom left the

neighborhood of a dopant. This means that the sites where the dopant has not lost

oxygen were very active in oxidation reactions. Above 400K almost all dopants

have an oxygen vacancy next to them and an oxidation reaction in such a system

takes place by creating a second vacancy. The energy required to form a second

vacancy was smaller on (110) than on (100). On the (110) surface, it was much

easier to form a second vacancy on the doped surface than the first vacancy on the

undoped surface. The energy required to form a second oxygen vacancy on (100)

was comparable to that of forming the first vacancy on the undoped surface. Thus

doping made the (110) surface a better oxidant but it has a small effect on the

oxidative power of the (100) surface. On the (110) surface CO adsorption results in

formation of a carbonate-like structure, similar to the undoped surface, while on the

(100) surface direct formation of CO2 was observed, in contrast to the undoped

surface. The Au dopant weakens the bond of the surrounding oxygen atoms to the

oxide making it a better oxidant, facilitating CO oxidation.

Vacancy Formation and CO Adsorption on Gold-Doped Ceria Surfaces. M.Nolan,

V.S.Verdugo, H.Metiu: Surface Science, 2008, 602[16], 2734-42