On the Nature of the Unusual Redox Cycle at the Vanadia Ceria Interface

This work investigates the effect of changing the vanadia/support interface on the redox properties of the material for the oxidative dehydrogenation reaction of small alkanes. In particular, ternary V2O5/CeO2/SiO2 catalysts are compared to vanadia on ceria and CeVO4 catalysts. Modifications in the CeO2 phase by the effect of the silica support and the creation of new V-Ce-Si interfaces induce substantial changes in the phases and behavior of vanadium species as well as CeO2, thus modifying the reaction mechanism. Powerful characterization techniques, XRD, in situ XANES, and Raman, as well as studies of ethane oxidative dehydrogenation catalytic activity provide a solid description of the phenomena associated with the different interfaces on a molecular level. Bulk CeO2 entities react with the vanadium species, leading to the formation of vanadate inhibiting the redox pair of V. These centers are very active but selective to ethane total oxidation. However, smaller ceria domains achieved by dispersion on a silica support do not undergo this solid-state reaction, resulting in new contacts with different behavior where both V and Ce participate. The extent of the participation and the reactivity depends also on the dispersion of both the ceria and the vanadium species. Vanadium polymeric species are more selective to ethene when dispersed on ceria entities with an epitaxial relationship between ceria and the underlying silica, which largely influences the properties of relatively small 3D-Ce particles and modifies the oxygen lattice lability. Therefore, how the electronic and structural properties of the support materials are modified affects vanadia reactivity, determining, in turn, the type and distribution of the V-O-Ce species, which might be the reason for the variation in reactivity and selectivity.