title: Application of AXAFS spectroscopy to transition-metal oxides: influence of the nearest and next nearest neighbour shells in vanadium oxides.
abstract: The influence of changes in coordination number, interatomic distances, and oxidation state on the intensity and centroid position of the Fourier transform (FT) of the atomic X-ray absorption fine structure (AXAFS) peak of vanadium oxide bulk model compounds and alumina-supported vanadium oxide clusters has been investigated. Using Na3VO4 and V2O5 as model compounds, it has been shown that the nearest neighbour shells have a pronounced influence on the AXAFS intensity; specifically, a 40 % decrease in intensity was observed between these two compounds. Secondly, the influence of partial reduction of the vanadium oxide species has been determined; this led to a 50 % decrease in the AXAFS intensity and to an increase in the centroid position. Furthermore, the influence of the vanadium oxide loading has been assessed. A non-linear relationship between the vanadium oxide loading and the AXAFS intensity has been found, indicating that the AXAFS intensity is sensitive to the formation of V-O-V bridging bonds between the vanadium VO4 clusters. The results show that AXAFS can be used to probe the relative energy level of the vanadium valence orbitals.
authors: Inorganic Chemistry and Catalysis Group, Department of Chemistry, Utrecht University, 3508 TB Utrecht, The Netherlands.
authors: Daphne E
authors: DE
authors: Keller
authors: Bert M
authors: BM
authors: Weckhuysen
authors: Diek C
authors: DC
authors: Koningsberger