Monolayer Detection of Supported Fe and Co Oxides on Ceria To Establish Structure–Activity Relationships for Reduction of NO by CO

A series of ceria-supported iron and cobalt oxide catalysts were synthesized with incremental metal loadings to determine within a narrow range the monolayer surface coverage. Onset of monolayer formation was monitored utilizing X-ray diffraction and Raman spectroscopy to identify the presence of microcrystalline Fe–oxide and Co–oxide phases. Formation of Fe 2 O 3 and Co 3 O 4 microcrystalline phases was found on the 5.40 Fe/nm 2 FeOx/CeO 2 and 2.58 Co/nm 2 CoOx/CeO 2 catalysts, respectively, and thus those surface densities approximate the monolayer coverage. The surface sensitivity of this approach was confirmed by corroborating the results with surface characterization by X-ray photoelectron spectroscopy. Catalytic activity testing was performed to illustrate the importance of establishing the monolayer coverage of each independent ceria-supported oxide system, that is, maximizing the number of metal–oxygen–support interfacial bonds. Steady-state activities for reduction of NO by CO in the presence of a stoichiometric amount of oxygen were monitored at 275 °C. Indeed, the maximum areal activity of the catalysts (0.0116 and 0.0386 μmol NO/m 2 /s) was found at or slightly above the approximated monolayer coverages for both supported iron or cobalt oxide catalysts, respectively. These results represent a broadening of the knowledge of monolayer oxide systems on the catalytically interesting CeO 2 support, and are expected to guide rational design of future improved catalysts for the industrially useful reaction of reduction of NO by CO in the presence of oxygen.