CO₂-Assisted Oxidative Dehydrogenation of Propane over VO_x/In₂O₃ Catalysts: Interplay between Redox Property and Acid−Base Interactions

In this work, a series of VO_x-loaded In₂O₃ catalysts were prepared, and their catalytic performance was evaluated for CO₂-assisted oxidative dehydrogenation of propane (CO₂-ODHP) and compared with In₂O₃ alone. The optimal composition is obtained on 3.4V/In₂O₃ (surface V density of 3.4V nm⁻²), which exhibited not only a higher C₃H₆ selectivity than other V/In catalysts and In₂O₃ under isoconversion conditions but also an improved reaction stability. To elucidate the catalyst structure−activity relationship, the VO_x/In₂O₃ catalysts were characterized by chemisorption [NH₃-temperature-programmed desorption (TPD), NH₃-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), CO₂-TPD, and CO₂-DRIFTS], H₂-temperature-programmed reduction (TPR), in situ Raman spectroscopy, UV−vis diffuse reflectance spectroscopy, near-ambient pressure X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and further examined using density functional theory. The In−O−V structure and the extent of oligomerization, which play a crucial role in improving selectivity and stability, were identified in the VO_x/In₂O₃ catalysts. In particular, the presence of surface VO_x (i) inhibits the deep reduction of In₂O₃, thereby preserving the activity, (ii) neutralizes the excess basicity on In₂O₃, thus suppressing propane dry reforming and achieving a higher propylene selectivity, and (iii) introduces additional redox sites that participate in the dehydrogenation reaction by utilizing CO₂ as a soft oxidant. The present work provides insights into developing selective, stable, and robust metal-oxide catalysts for CO₂-ODHP by controlling the conversion of reagents via desired pathways through the interplay between acid−base interactions and redox properties.