In Situ XAS Investigations of Chemical Oscillations in the Oxidation of Co on Supported Pd Catalysts

Abstract

AbstrPct. Self-sustained temperature as well as rate oscillations during the oxidation of CO at atmospheric pressure on sup ported Pd catalysts were studied in-sifu at the Pd K edge by employing energvdispersive XAS. From the absorption speca phase transition from palladium oxide to palladium clusters can be excluded as driving force of the observed oscillations. Nevertheless a constant phase correlation between edge position and the observed temperature oscillations could be revealed. This points toward a periodical surface oxidation 1 reduction process in phase with deactivation I activation cycles of the catalyst. Furthermore, an oscillatory behaviour in height and position of the first Pd peak could be seen in the radial distribution fun* tion. From theoretical cluster calculations using FEFF6 it can be deduced, that the evaluated oscillations in Pd wordination number and Pd-Pd distance indicate an oscillatory change of surface coverage h m CO to oxygen and vice-versa. Taking these swfacewverage oscillations and the periodical oxidation 1 reduction into account, a surface activation 1 deactivation process is proposed as kinetic mechanism for the observed chemical oscillations.

An investigation of structure, magnetic properties and magnetoresistance of Ni films prepared by sputtering

“…EXAFS is another effective way to obtain some information of the microstructure [18]. The EXAFS data of Ni films were analyzed using a standard WinXAS 97 procedure [19,20]. A cubic spline fit was used to remove the non-oscillatory background.…”

Structural and Electronic Properties of Sol−Gel Titanium Oxides Studied by X-ray Absorption Spectroscopy

“…The latter data were therefore more suitable for detailed consideration of the XANES while for EXAFS analysis we have analyzed data recorded with both Si(111) and Si(220) monochromators. Normalization of the spectra was performed using the program WINXAS, which fits a zero-order spline to a specified region after the edge step. Analysis of the EXAFS was performed with the programs XFIT and FEFFIT .…”

The “Realstruktur” of the System La2-xSrxCu1-yRuyO4-δ Studied by Rietveld and Extended X-ray Absorption Fine Structure Spectroscopy

“…For the evaluation of the EXAFS data, the program WinXAS was used. The preedges were normalized for absorbance by fitting the spectral region from 8.7 to 8.9 keV (Ru, 21.9−22.05 keV) with a Victoreen function and subtracting this as background absorption.…”