Doping of gold into ceria-based materials has been reported to greatly promote the catalytic activity for the low-temperature water-gas-shift (WGS) reaction. How exactly this promotion takes place and what kind of reaction mechanism, redox or formate, is valid for the Au-CeO₂ catalyst, is currently being debated in literature. Raman spectroscopy is a powerful technique for both structural detection in the lattice of metal oxides, and for the adsorbed surface oxygen species. In this paper, we use in-situ Vis-Raman measurement, with a green excitation of 488 nm wavelength, as a probing tool to study Au-CeO2 catalysts under either CO (1%CO/He) or WGS (1%CO+3%H₂O/He) conditions. The tested samples were prepared by co-precipitation (CP), urea gelation-coprecipitation (UGC) or deposition-precipitation (DP), and calcined in air at different temperatures (uncalcined, 200 and 400 °C). The main focused Raman bands located at ca. 460, 600, 820 and 1170 cm^-1 are related to the lattice CeO₂ T2G, oxygen vacancy, surface peroxide (O₂^2-) and superoxide (O₂^-) species, respectively. Typically, the 400 °C-calcined Au(0.5at%)-CeO₂ sample did not show any surface oxygen peaks at room temperature in air. After purging it in 1%CO/He gas at room temperature for 50 min, the surface peroxide peak appeared. As the temperature was raised, the amount of surface peroxide species dropped quickly, and was depleted completely at 100 °C. Upon cooling down, the surface peroxide peak was not recovered. The intensity of the oxygen vacany peak was almost the same throughout the whole measurement, while the lattice CeO₂ T2G peak became broader and shifted to lower wavenumber. A rather broad peak appeared at around 1100 cm^-1, which can be attributed to the second order CeO₂ 2LO peak. The in-situ Raman test under WGS condition diaplayed a different feature for the surface peroxide peak of this sample. As the temperature was raised, the amount of surface peroxide species dropped gradually from 100 °C, and was depleted completely at 200 °C. During cooling down in the reaction mixture, the peroxide peak was totally recovered at 100 °C and partially recovered at 30 °C, due to the water effect. These and complementary results will be presented to show that the surface oxygen species plays a crucial role for the WGS reaction on the gold doped ceria catalyst.

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