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

Abstract

Our recent work has reported that higher propylene selectivity and improved stability can be achieved by combining redoxactive VO x and basic In 2 O 3 for CO 2 -assisted oxidative dehydrogenation of propane (CO 2 -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 O 2 . Detailed characterizations have been performed to reveal the catalyst structure−performance relationship, including chemisorption (NH 3 /CO 2 -temperature-programmed desorption, NH 3 /CO 2 -TPD), H 2 -temperature-programmed reduction (H 2 -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 In 2 O 3 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 CO 2 -ODHP.

Revealing the mechanism of VOx/Ti3AlC2 for the dehydrogenation of propane

“…In conclusion, the configurations of VO x /Ti 3 AlC 2 catalysts are reasonably proposed based on previous reports 19,31,37,53 and the analysis of XRD, SEM, TEM, Raman, H 2 -TPR and XPS results. As shown in Fig.…”

Insights into the Molecular Structure of MoOx Catalysts via Static and Transient Raman Experimentation

“…This feature has been the focus of several literature reports due to its distinct behavior under the reaction conditions, and it is believed that it is associated with the stretching modes of Mo−O−X configurations, where X can be either another molybdenum atom (bridging bond in oligomers) and/or the cation of the support (anchoring bond). 7,23,32,41,48,49,52,53,55,63,73,74,83,86,87 Structural implications of this band are discussed in more detail in later sections.…”

“…Among the strategies to understand the issue of heterogeneity in dispersed oxide sites, in situ vibrational spectroscopy ,− has proved to be a powerful tool, able to provide molecular-level information on the structural response of deposited oxometallic phases. Particularly, both Raman and infrared (IR) spectroscopies have revealed that the arrangement of dispersed oxo-molybdenum species can vary greatly, especially when deposited on different metal oxide supports.…”