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Reactions of reduced cerium oxide CeO x with water are fundamental processes omnipresent in ceria-based catalysis. Using thin epitaxial films of ordered CeO x, we investigate the influence of oxygen vacancy concentration and coordination on the oxidation of CeO x by water. Upon changing the CeO x stoichiometry from CeO 2 to Ce 2 O 3, we observe a transition from a slow surface reaction to a productive H 2 -evolving CeO x oxidation with reaction yields exceeding the surface capacity and indicating the participation of bulk OH species. Both the experiments and the ab initio calculations associate the effective oxidation of highly reduced CeO x by water to the next-nearest-neighbor oxygen vacancies present in the bixbyite c-Ce 2 O 3 phase. Next-nearest-neighbor oxygen vacancies allow for the effective incorporation of water in the bulk via formation of OH – groups. Our study illustrates that the coordination of oxygen vacancies in CeO x represents an important parameter to be considered in understanding and improving the reactivity of ceria-based catalysts.
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Dvořák et al. (2018) studied this question.
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