Origin of the Activity Trend in the Oxidative Dehydrogenation of Ethanol over VO x /CeO 2 **

Abstract Supported vanadia (VO x ) is a versatile catalyst for various redox processes where ceria‐supported VO x have shown to be particularly active in the oxidative dehydrogenation (ODH) of alcohols. In this work, we clarify the origin of the volcano‐shaped ethanol ODH activity trend for VO x /CeO x catalysts using operando quick V K‐ and Ce L 3 ‐ edge XAS experiments performed under transient conditions. We quantitatively demonstrate that both vanadium and cerium are synergistically involved in alcohol ODH. The concentration of reversible Ce 4+ /Ce 3+ species was identified as the main descriptor of the alcohol ODH activity. The activity drop in the volcano plot, observed at above ca. 3 V nm −2 surface loading (ca. 30 % of VO x monolayer coverage), is related to the formation of spectator V 4+ and Ce 3+ species, which were identified here for the first time. These results might prove to be helpful for the rational optimization of VO x /CeO 2 catalysts and the refinement of the theoretical models.