Re: [Ifeffit] Ifeffit Digest, Vol 113, Issue 18

30 Jul 2012


      Hello Branko,
   I've worked a little bit with small Pt nanoparticles and I think I may
see a problem.  In the project file you sent us, you choose an Rbkg of 1.6
for your nanoparticles but 1.0 for the foil.  The Pt-O bonds at ~ 2 A end
up at about 1.5/1.55 A in the Fourier Transform, so your choice of Rbkg is
suppressing the real signal in that region.  I'd look again with a lower
Rbkg if you haven't already (1.2 is a good starting point).
   I didn't see your Pt-O standards in the project.
   Also keep in mind that Artemis will plot individual paths from the FEFF
calculation, which is really useful for determining if a specific path has
a strong contribution to your fit or if a pair of paths will be difficult
to distinguish.
   I hope that helps!
      Michael Weir


On Mon, Jul 30, 2012 at 9:01 AM,
wrote:
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Today's Topics:
1. Re: Ifeffit Digest, Vol 113, Issue 17 (Branko Zugic)
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Message: 1
Date: Mon, 30 Jul 2012 12:00:37 -0400
From: Branko Zugic 
To: ifeffit@millenia.cars.aps.anl.gov
Subject: Re: [Ifeffit] Ifeffit Digest, Vol 113, Issue 17
Message-ID:
        
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Hi Anatoly,
I've only tried approximating using the short bond at 2 A up until now.
Below are the spectra that I'm trying to interpret. These are merged QEXAFS
data taken at increasing temperature under WGS conditions. Perhaps I
haven't processed them well enough? There certainly seem to be changes
taking place during the course of reaction, which I'm trying to interpret.
Given that the material starts out very well dispersed (I've observed many
sub-nm Pt clusters via ac-STEM) and grow to 1-2 nm particles during
reaction, I would expect to observe corresponding structural changes during
reaction. I also observe significant changes in the EXAFS spectra when
alternating between WGS gas and He - hence my thought to including some
kind of Pt-C and Pt-O paths, similar to those used in the Ir4(CO)12 work.
Thanks for any help!
Branko
On Sat, Jul 28, 2012 at 1:00 PM,
wrote:
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Today's Topics:
1. Re: Modeling Pt/C Catalyst Under WGS Conditions
      (Anatoly I Frenkel)
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Message: 1
Date: Sat, 28 Jul 2012 01:02:23 +0000
From: Anatoly I Frenkel 
To: XAFS Analysis using Ifeffit 
Subject: Re: [Ifeffit] Modeling Pt/C Catalyst Under WGS Conditions
Message-ID: <98fc47e6-bd47-4c56-8fb2-3385fa7dbbbe@blur>
Content-Type: text/plain; charset="utf-8"
Maybe your system is more complex? Have you included a long Pt-O bond at
around 2.5 A or just a short one at around 2A? Hard to help without
seeing
what the problem is.
Anatoly
Sent from my mobile phone, please forgive typos
-----Original message-----
From: Branko Zugic 
To: "ifeffit@millenia.cars.aps.anl.gov" <
ifeffit@millenia.cars.aps.anl.gov
...
Sent: Fri, Jul 27, 2012 15:28:37 GMT+00:00
Subject: [Ifeffit] Modeling Pt/C Catalyst Under WGS Conditions
Hello,
I am trying to interpret some in-situ Quick-EXAFS and EXAFS data that I
took under water-gas shift conditions (CO + H2O diluted in He) on some
Pt/C
catalysts. I'm finding that the Pt-Pt and Pt-O fits using foil data, Pt-O
standards, and quick 1st shell approximations for Pt-O aren't that great.
After looking through the literature I came across some papers (i.e.
http://pubs.acs.org/doi/abs/10.1021/jp983283e) that use the Ir-O and
Ir-C
interactions from Ir4(CO)12 to approximate Pt-O and Pt-C interactions. I
then found some crystallographic tables for Ir4(CO)12 (below), but it's
unclear to me whether I can use this to create an atoms inp file (and
whether the data is for the structure I'm looking for or the referenced
Ir(CO)3). So far I've had no luck.
Is this a reasonable approach to this problem? Is the information I have
enough to do this? Any suggestions as to where I may be able to find the
crystallographic data I am looking for?
Branko Zugic
--
PhD Candidate
Tufts University, Chemical and Biological Engineering
4 Colby Street, Room 226
Medford, MA 02155
Ph: (O) 617 627 2267 (H) 508 414 8555
Email: Branko.Zugic@tufts.edumailto:Branko.Zugic@tufts.edu,
brankozugic@gmail.commailto:brankozugic@gmail.com