Effect of Structural Evolution of Gold Species Supported on Ceria in Catalyzing CO Oxidation

The intrinsic reactivity of atomically dispersed gold catalysts for low-temperature (L-T) CO oxidation remains an elusive issue. Here, two kinds of atomically dispersed gold with different loadings supported on nanoceria prepared via a deposition precipitation method were evaluated as catalysts for L-T CO oxidation. Much distinct differences in catalyzing CO oxidation behaviors were exhibited on the two kinds of gold catalysts. These weakly anchored gold species in the 1% Au/CeO2 (1 wt % gold loading) catalyst revealed increasing reactivity under the reaction condition, while these strongly anchored ones in the 0.5% Au/CeO2 (0.5 wt % gold loading) catalyst were inactive. For the 1% Au/CeO2 catalyst, in situ diffuse reflectance infrared spectroscopy (DRIFTS) proved gold species transformation from Aun+ (1 <= n < 3) to Au delta+ (0 < delta < 1), and simultaneously, aberration-corrected scanning transmission electron microscope measurements confirmed that partial atomically dispersed gold species transformed into gold clusters. While for 0.5% Au/CeO2, atomically dispersed Aun+ (1 <= n < 3) hardly varied in catalyzing CO oxidation at room temperature (RT). CO adsorption tests by in situ DRIFTS combining with the kinetics measurements demonstrated that these formed Au delta+ sites were much superior in adsorbing CO molecules than monodispersed Aun+ atoms at RT. Therefore, the gap in capturing CO molecules intrinsically resulted in the distinct catalytic performance for clustered Au delta+ (0 < delta < 1) and atomically dispersed Aun+ (1 <= n < 3).