The amount of oxygen vacancy was correlated with the Ce3+ concentration. As a result, the concentration of oxygen vacancy in Ru/CeO2 and CsRu/CeO2 catalysts was analyzed by XPS, following the method descried in reference [33], [34], [35]. The XPS high-resolution spectrum of Ce 3d was shown in Fig. 8. The peaks fitting was performed in MultiPak, original from the equipment’s company. Shirley-type background was used to remove the background from the spectrum before the peak fitting. The Ce 3d XPS region was fitted using the 10 peaks model as suggested in reference [33], [34], [35]. Those 10 peaks are originated from different Ce oxidation states (Ce3+ and Ce4+) and their 4f configurations which can be used to determine the percentage contributions of Ce3+ and Ce4+ ions (Table 2). The oxygen vacancy concentration was calculated by the ratio of the Ce3+ XPS peak area to the area of all Ce 3d peaks.

https://www.sciencedirect.com/science/article/pii/S0021951722002536

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