Origin of the high activity of mesoporous CeO₂ supported monomeric VO_x for low-temperature gas-phase selective oxidative dehydrogenation of benzyl alcohol: Role as an electronic "hole"

Herein, we report a newly developed mesoporous VO_x-CeO₂ catalyst with dominant monomeric VO_x species, which can promote the gas-phase ODH reaction of benzyl alcohol-to-benzaldehyde (BA-to-BAD) by molecular oxygen at a surprisingly low temperature range of 203-243 °C, with a high mass-specific activity of ∼25 mmol·g_cat^-1·h^-1 and TOF of 1367 h^-1. To the best of our knowledge, it appears to be the most effective transition metal oxides catalyst for the BA-to-BAD reaction in the gas phase. Experimental measurements and density functional theory (DFT) calculations suggest that the activities of VO_x-CeO₂ catalysts strongly depend on the polymeric states of surface VO_x, with monomeric VO_x giving much better performance than bigger VO_x clusters. It is important to highlight that a specific monomeric VO₃ species, only occurring under the reaction conditions, is identified for the first time to have the key influence on BA oxidation. Moreover, it has been found that the origin for the unique activity of such monomeric VO_x-CeO₂ can be attributed to its electronic "hole" structure.