Structure and activity of mixed VO_x-CeO₂ domains supported on alumina in cyclohexane oxidative dehydrogenation

Alumina-supported VO_x-CeO₂ materials are synthesized by atomic layer deposition (ALD) and evaluated in cyclohexane oxidative dehydrogenation (ODH). The order of deposition of the two metal oxides by ALD influences the size, geometry and oxidation state of the resulting surface species as indicated by Raman spectroscopy coupled with density functional theory (DFT) calculations and XPS. The individual contributions of VO_x and CeO₂ surface sites to the cyclohexane ODH reaction mechanism are investigated through a comparison of the catalytic activity of the supported mixed metal oxide materials, VO_x/Al₂O₃, VO_x/CeO₂ and a bare CeO₂ support. The highest activity is observed for CeO₂, and different surface active sites are distinguished by introducing cyclohexane and cyclohexene in the reactant feed mixture. The catalytic behavior is dependent on the nature of V–O–S (S, Support) bonds, and small clusters of CeO₂ on Al₂O₃ favor total oxidation, similar to exposed CeO₂ sites in VO_x/CeO₂.