You right too assuming that there is an H2 adsorbed. In reality, this is a sample catalyst of 1%Pt supported in Al2O3 that was treated in H2. The data of EXAFS was colleted at 500ºC in an flux of H2. It is a catalysts prepared by impregnation method. In the fit model I assuming that is possible to has a oxigen neighbor to Pt, therefore, there is a PtO2 model atom to do the fit. They work well with one path unless by the peak at 1A. I already thought to assuming a H atom neighbor to Pt but, I not find a good model to this. Do you have some idea if is possible to do that? Do you belives that I should take more than one path for Pt-Pt distance?

2009/1/13 Carlo Segre <segre@iit.edu>

Hi Kleper:

There is a single Pt-Pt path in your fit. This is effectively a fcc Pt
distance of 2.77. I see several problems:

This spectrum has distances which are much shorter than 2.77 and so I
would expect that this single path would not be a very good fit. I am not
sure if the peak around 1.1A is real, but it could be given the hydrogen
that you indicate is present in the file name. What is clear is that the
bigger peaks are not Pt-Pt peaks at all. The Pt-Pt peak will usually
appear around 2.5A in Chi(R).

The second thing that I noticed, is that you must have a problem with your
installation of the software because I just took your file and executed
the fit and did not get the strange values for Chi^2 and reduced Chi^2
that you have posted. The value for amp is negative, indicating that the
path is not a good model, but the Chi^2 I got was around 1000.

I can't tell much form the name of your file but I suspect that you have
Pt-Al and possibly Pt-H distances in your sample. Do you have any other
information about this sample?

Carlo

--
Carlo U. Segre -- Professor of Physics
Associate Dean for Special Projects, Graduate College
Illinois Institute of Technology
Voice: 312.567.3498 Fax: 312.567.3494
segre@iit.edu http://www.iit.edu/~segre segre@debian.org

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