Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 59: Oxides and Insulators: Clean Surfaces
O 59.6: Vortrag
Donnerstag, 29. März 2007, 17:00–17:15, H41
Identification of reactive oxygen sites at surfaces of MoO3 by polarization–resolved NEXAFS spectra: theoretical studies — •Matteo Cavalleri and Klaus Hermann — Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany
The identification of reactive oxygen sites at metal oxide surfaces and the characterization of their physical properties is of great importance for an understanding of the catalytic activity of such materials and, thus, for a rational design of more efficient and selective catalysts. Here we evaluate Near–Edge X–Ray Absorption Fine Structure (NEXAFS) spectra, based on density functional theory and appropriate surface clusters, to study and discriminate non–equivalent oxygen centers present at surfaces of catalytically relevant molybdenum oxides. For the (010) surface of bulk MoO3 this technique is able to unambiguously distinguish between singly coordinated molybdenyl oxygen covering the topmost molybdenum layers and other oxygen centers of similar local environment, differing only by their spatial orientation in the crystal. Theoretical predictions are also successfully used to identify and interpret characteristic features in the NEXAFS spectrum that arise from defects and oxygen vacancies1. Upon comparison between measured and computed NEXAFS spectra for different photon polarization directions it is also possible to validate proposed structures of thin MoO3 films at the Au(111) surface.
1 M. Cavalleri, K. Hermann, S. Guimond, Y. Romanyshyn, H. Kuhlenbeck and H.–J. Freund, submitted to Cat. Today (2006)