Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 13: Heterogeneous Catalysis

O 13.1: Vortrag

Montag, 25. Februar 2008, 14:00–14:15, HE 101

Geometry of silica supported vanadium oxide particles: theoretical core excitation spectra can provide new insight. — •Matteo Cavalleri and Klaus Hermann — Fritz-Haber-Institut der MPG, Berlin, Germany

The characterization of vanadia units in supported vanadium oxide catalysts is of paramount importance for an understanding of the reactive behavior of these materials.

Here we compare results from density-functional theory calculations on O 1s core excitations of small model particles with experimental data from Near-Edge X-ray Absorption Fine Structure (NEXAFS) measurements of well-known reference compounds and of real catalytic materials in order to determine structural properties of silica-supported vanadia nanoparticles. This procedure provides an unambiguous discrimination of all different oxygen species inside the particles and overcomes limitations of previous studies using vibrational spectroscopy where the particle-support interaction was found to hide essential structural information.

As a result, we are able to identify unique spectroscopic features characterizing bridging V-O-V oxygen that can be used as a fingerprint of polymeric vanadia species. The O 1s excitations of the silica support are found to contribute to the NEXAFS spectrum at higher energies compared with those of the vanadia particle such that the two contributions can easily be separated in the experiment.