(583ad) A DFT Theoretical Study of Ethylbenzene Dehydrogenation to Styrene With CO2 Over V2O5(001)

The dehydrogenation of ethylbenzene (EB) to produce styrene (ST) in the presence of CO₂ instead of steam is remarkable energy saving and environmentally friendly. Various catalysts are active for the dehydrogenation of EB in CO₂. Among these catalysts, the supported V catalysts exhibit good performance. However, the V catalysts have weak stability, mainly due to the reduction of high valence V species and the lattice oxygen loss. These inferences are only based on the experimental analysis.

As the V₂O₅(001) is the most stable surface of V₂O₅ crystal, the first detailed periodic density function theoretical (DFT) study were employed to explore the mechanism for EB dehydrogenation and the role of CO₂ on V₂O₅(001) surface, in order to elucidate the cause of the catalyst deactivation. Two mechanisms, namely the coupling mechanism and the redox cycle mechanism, are traditionally proposed for EB dehydrogenation with CO₂. Various active sites and reaction mechanisms were examined. Results showed that the first C-H bond activation was the rate limiting step of the reaction. The most feasible pathway for the C-H bond activation was predicted to take place at the bridging V-O-V site, the less active site was the vanadyl V=O site. Then, the H atoms were abstracted by lattice O to form H₂O, leading to the reduction of V₂O₅(001) surface. As CO₂ decomposition was hindered by the relatively high activation energies, CO₂ cannot serve as the oxidant to recover the surface to keep the redox cycle. Above all, the V catalyst should introduce the materials with the oxygen storage/release capacity to get the high catalysts stability.