Effect of the Molecular Structure of Surface Vanadia on Activity and Regenerability of VO_x/In₂O₃ Catalysts for CO₂-Assisted Oxidative Dehydrogenation of Propane

Our recent work has reported that higher propylene selectivity and improved stability can be achieved by combining redox-active VO_x and basic In₂O₃ for CO₂-assisted oxidative dehydrogenation of propane (CO₂-ODHP). In the present work, we continued to explore the stability and regenerability of V/In catalysts. In particular, our interest lies in identifying the effect of mono- and polyvanadate on catalytic performance and regenerability. A V/In catalyst with an increased proportion of monovanadate was prepared using the Schlenk line under moisture-free conditions (V/In-S), while the fully polymerized vanadate catalyst was prepared through a regular impregnation (V/In) for comparison. The Schlenk-line-prepared catalyst, namely, V/In-S, not only exhibits a 17-30% enhanced propylene yield at high temperatures (500-540 °C) over V/In but also presents improved stability and regenerability with nearly 88% activity recovered after regeneration in O₂. Detailed characterizations have been performed to reveal the catalyst structure-performance relationship, including chemisorption (NH₃/CO₂-temperature-programmed desorption, NH₃/CO₂-TPD), H₂-temperature-programmed reduction (H₂-TPR), and spectroscopic studies [Raman spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-vis DRS), near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS), and high-sensitivity low-energy ion scattering (HS-LEIS)]. Characterization results demonstrate that compared with polyvanadates, monovanadates lead to strengthened interaction with In₂O₃ and a more stabilized V/In surface and subsurface, as well as improved redox properties of VO_x. These advantages give rise to the observed enhancement in activity, stability, and regenerability. These findings advance the understanding of the relationship between the activity/stability and the molecular structure of surface oxide species (vanadia) and the interplay between acid-base interactions and redox properties of mixed metal-oxide catalysts for efficient CO₂-ODHP.