General information
| Title: | Periodic DFT calculations on structure, dynamics and reactivity of vanadium oxide aggregates |
| Research areas: | Theoretical chemistry |
| Leader: | Dr. Maria Veronica Ganduglia-Pirovano Humboldt-Universität, Institut für Chemie Unter den Linden 6 10099 Berlin Sitz: Brook-Taylor-Str. 2, 12489 Berlin Telefon: 030-2093-7139 Telefax: 030-2093-7136 E-Mail-Adresse: vgp@chemie.hu-berlin.de |
Prof. Dr. Joachim Sauer Humboldt-Universität, Institut für Chemie Unter den Linden 6 10099 Berlin Sitz: Brook-Taylor-Str. 2, 12489 Berlin Telefon: 030-2093-7134 Telefax: 030-2093-7136 E-Mail-Adresse: sek.qc@chemie.hu-berlin.de |
Abstract:
In the first two funding periods vanadium oxide
films and clusters on α±-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 α±-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 VV to VIV of two cations per defect instead of
creating a VIII-center. 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
γ-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