Active Sites and Mechanism of the WGS Reaction Over Ceria-Based Gold Catalysts

5 Active Sites and Mechanism of the WGS Reaction Over Ceria-Based Gold Catalysts 

Additional evidence for the presence of oxygen vacancies or Ce defects on a reduced Au/ceria catalyst was produced after the admission of oxygen on preadsorbed CO over a reduced sample. An immediate depletion of the band at 2060 cm occurred, accompanied with the appearance of a new, more intense band at 2127 cm and a weak band at 2343 cm due to the formation of COg. The band at 2127 cm was due to CO co-adsorbed with oxygen species on gold step sites, close to the Ce % where oxygen 

In the spectra for MDP-prepared catalysts only a very weak and broad band at 2078 cnr was observed. The integrated area of this band was 1.72, one order of magnitude lower than the integrated area of the band at 2060 cm in the spectrum of a DP-prepared catalyst (18.31). These features are in good agreement with XPS data showing lower An concentration on the surface of the less active MDP-prepared gold-ceria catalyst. 

In situ characterization with X-ray absorption spectroscopy was used to determine the chemical state of the gold during the WGSR over an Au/ceria catalyst. The data indicated that cationic Au species present in fresh AuOyGeOg catalysts do not exist under reaction conditions and they could not be the active sites. The authors concluded that the rate-determining steps for the WGS at temperatures above 250 °C occur at the gold-ceria interface, with the active 

Theoretical studies of Au on CeOj (111), which typically consider the interaction of the surface vdth individual Au atoms, are based on periodic DFT. In the first density functional calculations to consider the adsorption of gold on ceria Liu et suggested that at the atop site of a perfect CeOj (111) terrace Au acquires some positive charge leading to a reduced Ce cation. On the basis of this assumption the authors demonstrated preferential Au adsorption 

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