[Ifeffit] white line intensity v. edge position in determining oxidation state of Re

[Bare, Simon R]

Edward:

For rhenium the examples published in the literature use the first
inflection point to define the oxidation state. Indeed for a set of
rhenium oxides of formal oxidation state 4, 6 and 7 there is close to a
linear relationship of formal oxidation state with edge position. We
have collected such data several times.

Regarding your other point about the white line intensity of rhenium
nanoparticles, this has been the subject of some recent research of
ours. We are close to submitting a manuscript where we discuss this
point for rhenium supported on alumina. We also observe the same
phenomena that you describe: even though the rhenium is formally
reduced, the white line intensity is substantially more intense that the
equivalent metal reference. Until this manuscript is ready I refer you
to an older publication: J. Phys. Chem. 95 (1991) 225-234 by Fung et al.
where they also note the same.
We have also done some FEFF8 XANES calculations of small Re clusters and
there is a clear trend of increasing white line intensity with
decreasing cluster size.

I would be willing to share our rhenium reference spectra if you contact
me directly.


Simon R. Bare
 
Senior R&D Associate
UOP LLC
25 East Algonquin Road
Des Plaines, IL 60017-5017
Phone - 847.391.3171
Cell - 630.842.6890
Fax - 847.391.3719
simon.bare at uop.com
www.uop.com
 
 
 

-----Original Message-----
From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Edward
L. Kunkes
Sent: Thursday, May 17, 2007 10:29 AM
To: ifeffit at millenia.cars.aps.anl.gov
Subject: [Ifeffit] white line intensity v. edge position in determining
oxidation state of Re

Hi everyone,


 I am trying to determine the oxidation state of Re in PtRe
nanoparticles catalysts supported on carbon.
The ReLIII edge was measured before and after an in-situ reduction in
hydrogen.
Can anyone suggest Which characteristic of the edge is more related to
oxidation state ? Is it the 
integrated white-line intensity or the position of the edge(point of
maximum derivative). The edge 
position of the ReLIII edge of my particles is the same as that of Re
foil, however the
white line instensity is significanty higher. For the non-reduced PtRe
particles, the edge position is
similar to that of ReO2 (with a larger white line intensity). 


 Also, does anyone have any Data on Re-foil, HReO4 and ReO2 so that i
can compare it to the data
i measured for my standards ?


 Thank you very much for your help


-Edward Kunkes 
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