CO Oxidation on Inverse CeOx/Cu(111) Catalysts: High Catalytic Activity and Ceria-Promoted Dissociation of O2

A Cu(111) surface displays a low activity for the oxidation of carbon monoxide (2CO + O-2 -> 2CO(2)). Depending on the temperature, background pressure of O-2, and the exposure time, one can get chemisorbed O on Cu(111) or a layer of Cu2O that may be deficient in oxygen. The addition of ceria nanoparticles (NPs) to Cu(111) substantially enhances interactions with the O-2 molecule and facilitates the oxidation of the copper substrate. In images of scanning tunneling microscopy, ceria NPs exhibit two overlapping honeycomb-type moire structures, with the larger ones (H-1) having a periodicity of 4.2 nm and the smaller ones (H-2) having a periodicity of 1.20 nm. After annealing CeO2/Cu(111) in O-2 at elevated temperatures (600-700 K), a new phase of a Cu2O1+x surface oxide appears and propagates from the ceria NPs. The ceria is not only active for O-2 dissociation, but provides a much faster channel for oxidation than the step edges of Cu(111). Exposure to CO at 550-750 K led to a partial reduction of the ceria NPs and the removal of the copper oxide layer. The CeOx/Cu(111) systems have activities for the 2CO + O-2 -> 2CO(2) reaction that are comparable or larger than those reported for surfaces of expensive noble metals such as Rh (111), Pd(110), and Pt(100). Density-functional calculations show that the supported ceria NPs are able to catalyze the oxidation of CO due to their special electronic and chemical properties. The configuration of the inverse oxide/metal catalyst opens new interesting routes for applications in catalysis.