Unraveling the Low-Temperature Redox Behavior of Ultrathin Ceria Nanosheets with Exposed {110} Facets by in Situ XAFS/DRIFTS Utilizing CO as Molecule Probe

Ultrathin ceria nanosheets with exposed reactive {110} facets are synthesized to evaluate the influence of its unique nanostructure on the low-temperature redox behavior. Via a systematic comparison of the ceria nanosheets with nanorods and nanoparticles, we demonstrate that the nanosheets show the enhanced redox reaction activity and the reduced reduction temperature. Through in situ XAFS experiments, we disclose that the ultrathin nanosheets intrinsically decrease the coordination number of Ce atoms and increase the disorder of ceria face-centered cubic fluorite structure, ultimately enhance the oxygen reactivity as well as mobility. Remarkably, the nanosheets exhibit the temperature-independent reducibility between 150 and 250 degrees C. Through in situ DRIFTS experiments, we demonstrate that the unidentate carbonates are probably the most active surface carbonates species on the redox reaction. The bidentate carbonates are speculated to be the main carbonate species as CO molecules adsorb and diffuse on the nanosheets surface. The blue shift of the band of the unidentate carbonates species on the nanosheets is consistent with the enhanced oxygen reactivity. We combine the oxygen reactivity with the variation of carbonate species to unravel the integral low-temperature redox behavior of the ultrathin ceria nanosheets.