A Thermally Stable Cr-Cu Nanostructure Embedded in the CeO2 Surface as a Substitute for Platinum-Group Metal Catalysts

High catalytic activities for CO-O-2 and CO-NO reactions that were superior to or comparable with those of platinum-group metal catalysts were achieved by synchronous dual-mode arc plasma deposition of a very small amount of Cr and Cu (0.07 wt % each) onto CeO2, followed by subsequent thermal aging at 900 degrees C for 25 h. The turnover frequency for CO oxidation over Cr Cu/CeO2 was 3-fold higher than that over Cu/CeO2 and exceeded values for the Rh, Pd, and Pt catalysts loaded on CeO2, despite a significant decrease in the surface area from 169 to 5 m(2) g(-1) caused by thermal aging. Experimental structure characterization and density functional theory calculations based on CeO2 (111) surface slab models revealed that Cu+ substitution for surface Ce atoms leads to the formation of asymmetric 3-fold oxygen coordination sites capable of efficient CO chemisorption and catalytic activity. In addition, Cr3+ was incorporated into the surface structure of CeO2; it plays an important role in enhancing the surface concentration of Cu+. A CO oxidation rate with nearly zero partial orders with respect to O-2 and isotopic (CO)-O-16-O-18(2) reactions yielding (CO2)-O-16 as the primary product demonstrated that the reaction proceeds via the Mars-van Krevelen mechanism.