An isotope-free transient kinetic approach to probe reactivity during the oxidative scission of ketones over VO_X/ γ-Al₂O₃

Although the oxidative scission mechanism of carbonyl compounds over alumina-supported vanadium oxides has been extensively studied, quantifying surface kinetic parameters under steady-state conditions remains challenging with conventional techniques such as temperature-programmed desorption (TPD). In this work, we establish an isotope-free transient kinetic approach to investigate the oxidative scission of ketones over VO_X/γ-Al₂O₃ with surface vanadium loadings ranging from 0.03 to 8 V·nm^{− 2}. Before kinetic measurement, the materials were characterized by Raman and UV-vis spectroscopy. Vanadium species on the inert support were found to exist as isolated tetrahedral VO₄ units at loadings below 0.8 V·nm^{− 2}, polymeric vanadate networks (V–O–V) at 0.8–4 V·nm^{− 2}, and crystalline V₂O₅ appearing only above monolayer coverage (≥8 V·nm^{− 2}). Two unlabeled ketones with similar structures were selected as probe reactants, enabling the determination of key kinetic parameters, including the quantity of surface intermediate, mean residence time, surface coverage, and site time yield. The transient profiles revealed two distinct turnover regimes. Specifically, rapid turnover sites were responsible for aldehyde and acid production, and slow turnover was associated with the delayed desorption of unreacted 5-nonanone. Correlating the microkinetic parameter with spectroscopic characterization demonstrated that polymeric vanadate species render the catalyst with the highest oxidative scission activity and site time yields, whereas isolated VO₄ units and V₂O₅ can limit the reactivity. The isotope-free transient approach provides a reliable methodology for quantifying microkinetic parameters under steady-state conditions and offers mechanistic insights into structure-reactivity relationships in VO_X/γ-Al₂O₃ catalyst.