Investigation of the CO₂ Activation and Regeneration of Reduced VOₓ/CeO₂ Catalysts Using Multiple In Situ Spectroscopies

Ceria‐supported vanadium oxide (VOₓ/CeO₂) is an important catalyst for various oxidation reactions. Recently, vanadia has emerged again as a less toxic alternative to CrOₓ‐based catalysts for the CO₂‐assisted oxidative dehydrogenation (ODH) of alkanes. To establish a mechanistic understanding of catalyst regeneration during CO₂ exposure, often described as the rate‐limiting step of these reactions, we investigated the regeneration of VOₓ/CeO₂ catalysts with different vanadia loadings using multiple in situ spectroscopies, that is, multi‐wavelength Raman, UV‐Vis, IR and X‐ray photoelectron spectroscopy. Time‐dependent analysis reveals that ceria is only partially regenerated in the bulk but fully regenerated in the subsurface. At the surface, stable carbonates form at vacancies, which are able to regenerate the lattice and deactivate ceria surface oxygen. The VOₓ/CeO₂ samples show a loading‐dependent behavior, with low‐loaded samples regenerating vanadia only partially, due to the high concentration of monomers, while at higher loadings, vanadia can be almost fully regenerated due to the higher nuclearities being thermodynamically more stable. Ceria is regenerated faster than vanadia, indicating that vanadia regenerates by oxygen spill‐over from the ceria lattice. Our results provide important mechanistic insight into CO₂ activation over supported vanadia catalysts, which is of great relevance for CO₂‐assisted ODH reactions.