The active role of the support in propane ODH over VOx/CeO2 catalysts studied using multiple operando spectroscopies

Abstract

Because of the relevance of supported vanadia catalysts for the oxidative dehydrogenation (ODH) of alcohols and short alkanes, a detailed mechanistic understanding, including the role of the support, is of great importance. In this work, we address the ODH of propane over ceria-supported vanadia (VOx/CeO2) catalysts, especially regarding the active participation of ceria and the synergy effect between ceria and vanadia. A combination of operando multi-wavelength Raman-, operando UV-Vis- and operando IR spectroscopy is applied, including the targeted use of different Raman excitation wavelengths to selectively enhance vibrational features through resonance from vanadia (514 nm) and the ceria support (385 nm). Our operando results show that surface lattice oxygen from ceria is crucial for the selective oxidation of propane while the structure of vanadia seems to stay unchanged during the reaction. Rather vanadia structures play an indirect role in increasing the overall selectivity of the reaction. The surface oxygen defects of ceria are affected by the interaction with vanadia monomeric species in direct proximity, owing to an irreversible occupancy of the vacancies by vanadia monomers, which slows down the overall oxygen dynamics and thereby decreases the amount of CO2 produced. Dimeric and oligomeric vanadia species weaken the adsorption of propane onto the ceria surface, further increasing the selectivity. Our mechanistic insights demonstrate the synergy effect between vanadia and ceria in oxidation reactions and provide an experimental basis for a detailed understanding of the role of the support in VOx/CeO2 and other supported vanadia catalysts.