Water-Gas Shift Reaction on Supported Gold

3 Water-Gas Shift Reaction on Supported Gold Nanoparticles 

At temperatures above 200°C, when significant WGS activity was detected, the line shape of the Au L3 edge resembled that of pure gold. The XANES spectra in Fig. 6.4 were obtained under a reaction mixture of 5% CO and 3% HgO in He (total flow 10 ml/min).  

Similar results were found when using a 1% CO and 3% HgO in He reaction mixture. Thus, the in situ time-resolved XAS data indicate that cationic Au species cannot be the key sites responsible for the WGS activity, because they do not exist under reaction condi-tions. An identical finding has been reported for AnO / Cei xZrx02 y powder catalysts. In these catalysts, the active phase 

5 Time-resolved X-ray dilfiaction patterns collected in situ during the WGS reaction over a 5% CuO-CeOj catalyst. The transformation of CuO into Cu occurs near 200°C before significant activity for the production of Hj was observed.  

The active phase of CuO-CeOg WGS catalysts was also investigated. The results of in situ time-resolved XRD (Fig. 6.5) and XAS (not shown) point to a complete reduction of the CuO to metallic Cu before the catalysts become active for the WGS. This reduction of the CuO is consistent with the behavior observed for CuO/ZnO catalysts and other Cu-based catalysts.As in the case of AuOx-CeOg, the active phase of CuO-CeOg catalysts contains nanoparticles of the noble metal disperse d on a partially reduced ceria support. The same is valid for Pt-CeOg and Pd-CeOg catalysts. 

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