Crucial role of H and O spillover in VOx/CeO2 catalysts reduction and re-oxidation during the ODH reaction

Abstract

Ceria-supported monomeric vanadia (VOx/CeO2) catalysts show outstanding activity in oxidative dehydrogenation (ODH) in the CO2 atmosphere. This work reports the density functional theory calculations exploring the reduction and reoxidation mechanisms in the Mars-van-Krevelen cycle for the ODH over VOx/CeO2(111). Intriguingly, a new phenomenon was observed in the reduction of VO2/CeO2(111), the H species generated by CH bond activation on the VOx cluster could spill over to CeO2 with a minimum barrier, enabling the reduction to occur at CeO2 substrate. Subsequently, the formed H2O releases and causes a structure evolution, resulting in VO2/CeO2(111) reduction to VO/CeO2(111). However, this H spillover is hard to be detected at the interface of VO/CeO2(111), VOx/TiO2(101), and VOx/α-Al2O3(001) due to a higher barrier, indicating that the H spillover is related to the electron acceptability of substrate and the structure of VOx cluster. Moreover, O spillover from CeO2 is noticed at the interface of VOx/CeO2(111) in the reoxidation process, causing the V oxidation to VO. However, VO reoxidation to VO2 is thermodynamically and dynamically unfavorable. Therefore, the structure VO/CeO2(111) seems to be conserved in the steady-state reaction process. This paper would provide key insights for understanding the structure evolution of catalyst in the ODH.