(583ad) A DFT Theoretical Study of Ethylbenzene Dehydrogenation to Styrene With CO2 Over V2O5(001)
AIChE Annual Meeting
Wednesday, November 6, 2013 - 6:00pm to 8:00pm
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.