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

Abstract

In this work, a series of VOx-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 VOx/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 VOx/In2O3 catalysts. In particular, the presence of surface VOx (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.