Hybrid DFT small-cluster model of CO oxidation on CeO2/(110)

Abstract

Only a few studies have examined oxidation of CO on pure CeO2. Here we describe reaction on the (110) surface of CeO2 with DFT and B3LYP calculations of small clusters, Ce5O12 and Ce6O12. We identified a weak adsorption site (0.21 eV) on top of a cerium atom and a strong site (2.31 eV) binding two oxygens to form a carbonate species. These energies are in accord with previous reports including GGA + U. Increasing the cluster size from Ce5O12 and Ce6O12 to Ce9O12 had no significant effect on the outcome. In addition a Mars-van Krevelen type reaction cycle is investigated involving the reaction of CO with a surface oxygen. A secondary pathway was discovered forming a very stable carbonate species, with the reversible reaction having a high activation barrier. This study is the first to find evidence of an activation barrier for the formation of a carbonate species as an alternative pathway to the desorption of CO2 on CeO2/(110), which would otherwise block the surface activity. We find the approach of modelling catalyst activity using a reduced cluster of atoms is accurate, flexible and advantageous.