Origin of the Activity Trend in the Oxidative Dehydrogenation of Ethanol over VO_x /CeO₂

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 L₃ - 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 Ce⁴⁺ /Ce³⁺ 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 V⁴⁺ and Ce³⁺ species, which were identified here for the first time. These results might prove to be helpful for the rational optimization of VO_x /CeO₂ catalysts and the refinement of the theoretical models.