Berlin 2015 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

O: Fachverband Oberflächenphysik

O 6: Catalysis

O 6.1: Vortrag

Montag, 16. März 2015, 10:30–10:45, MA 043

Support Effect in Oxide Catalysis: Methanol Oxidation on Vanadia/Ceria — Thomas Kropp, •Joachim Paier, and Joachim Sauer — Institut für Chemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany

We present a detailed mechanistic description of the methanol oxidation to formaldehyde at the VO_x/CeO₂(111) catalytic system employing the DFT+U approach as well as hybrid functionals to assess selected results. Compared to clean ceria (and depending on the pathway), depositing VO₂ on the surface does not affect significantly intrinsic barriers (1.3 eV) in the rate-determining H-transfer. It rather substantially increases the adsorption energy, which in turn leads to negative apparent barriers. The previously discussed pseudo vacancy, a structural feature of VO_x-decorated ceria, appears to be a favorable adsorption site for the methanol. Its dissociative adsorption at this very site, which is created by a oxygen spillover process from the support to the catalyst, was found to be as exothermic (-1.9 eV) as its adsorption at vanadium, i.e. insertion into the V-O_surf bond, since both processes heal the aforementioned pseudo vacancy. Besides the above mentioned ease in transferring electrons from V 3d states to Ce 4f states, the pseudo vacancy is inherently related to surface morphology and represents another cooperative effect between catalyst and surface. Both, a highly exothermic adsorption step as well as a lowering of the activation energy in the rate-determining step explain the higher activity of VO_x/CeO₂(111) compared to an inert SiO₂ support.