SFB 546 II-III: Periodic DFT calculations on structure, dynamics and reactivity of vanadium oxide aggregates (TP C 5)


In the first two funding periods vanadium oxide films and clusters on alpha±-Al2O3(0001) as well as the single-crystal V2O5(001) surface were examined concerning their reducibility. A substantial aspect of these investigations was the analysis of the stability of supported vanadium oxide aggregates and defective V2O5(001) surfaces of different composition as a function of temperature and the oxygen partial pressure (and additionally the vanadium chemical potential vanadium (or concentration) in the case of the supported systems) with the help of statistical thermodynamics. The phase diagrams show that under reducing conditions (e.g., UHV and 800 K) vanadyl oxygen atoms (O=V) are a prevalent feature of the stable surfaces termination of alpha±-Al2O3 supported species, which explains experimental findings of the TP C1 and B1. The formation of isolated defects on the V2O5(001) surface is energetically less costly than on the investigated supported systems. A reason for it is the delocalization of the two electrons that results in the valence change V-V to V-IV of two cations per defect instead of creating a V-III-centre. The progressive reduction of the V2O5-surface proceeds via the formation of defect pairs and rows oriented along the [010] direction, which can represent the initial stage of a fairly extended surface reduction. Investigations at (001) the surface of the V2O5 gamma-polymorph permitted forecasts over the reactivity of the model catalysts examined in TP B2.
In the next period the investigation of the support effect will be continued to deepen our understanding of possible structure-reducibility and/or reactivity relationships. Oxide supports such as TiO2, ZrO2 and CeO2 will be considered, since these lead to a higher chemical activity of the catalysts than pure V2O5. The emphasis will be on the chemisorption (e.g. of H, H2, methanol) and reactivity investigations. As reactions, the oxidation from adsorbed H2 to H2O and from methanol to formaldehyde, which leads both to an O-defect and an adsorbed H2O are of interest. The investigations will be performed using the Nudged Elastic Band approach. For the localization of transition structures results of the TP A4 will be of great value. Beyond that the question about the stability of other surface orientations of the V2O5 for different temperatures and H2O is partial pressure of interest.

Principal Investigators
Sauer, Joachim Prof. Dr. rer. nat. Dr. h.c. (Details) (Collaborative Research Centre 546 'Transitional Metal Oxide Aggregates')

Duration of Project
Start date: 07/2002
End date: 06/2011

Last updated on 2020-10-03 at 16:30