Collaborative Research Centre 546

"Structure, Dynamics and Reactivity of Aggregates of Transition Metal Oxides"

Project A4
 

General information
 

Title:

DFT calculations on structure, vibrational spectra and reactivity of different vanadium oxide aggregates

Research areas:

Theoretical chemistry, quantum chemistry

Leader:

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 previous funding period finite-size models for vanadium oxide species on SiO₂ supports have been designed and successfully tested. In cooperation with projects B1 and B3 we were able to solve the problem of the correct assignment of Raman bands to isolated monomeric and dimeric vanadium oxide species on SiO₂ and Al₂O₃ supports.
The structure predictions for V₂O₅ clusters in the gas phase, previously made by DFT, have been confirmed by spectroscopic experiments in project A3 and by ab initio calculations in project A1.
Dissociation of the vanadyl (V=O) bond has been chosen as test reaction for reactivity differences between gas phase V₂O₅ clusters and cluster ions, V₂O₅ surface species on supports and surfaces of crystalline V₂O₅. The observed support effects can be explained by supression of structure relaxations that are possible in crystalline V₂O₅ and by electronic site isolation.
In the next period quantum chemical studies will focus on elementary catalytic steps and again, comparison will be made between gas phase clusters (see also projects A2 and A3), supported species and surfaces of bulk materials (projects B2 and B3) . The studies on supported species, in additon to SiO₂ and Al₂O₃, will include a support material that is known to increase the activity of the catalyst compared to pure V₂O₅ such as TiO₂. Different local structures of the supporting oxides will be studied by QM/MM hybrid methods. The following reactions will be considered: oxidation of methanol to formaldehyd (some results already available) and oxidative dehydrogenation of propane yielding propene. To deepen the understanding of reactivity, some comparison will be made with other transition metal oxides (Niobium, Molybdenum).

Publications