[Ifeffit] Ifeffit Digest, Vol 113, Issue 18
Michael Weir
mgweir at gmail.com
Mon Jul 30 15:47:44 CDT 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,
<ifeffit-request at millenia.cars.aps.anl.gov>wrote:
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> Today's Topics:
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> 1. Re: Ifeffit Digest, Vol 113, Issue 17 (Branko Zugic)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 30 Jul 2012 12:00:37 -0400
> From: Branko Zugic <brankozugic at gmail.com>
> To: ifeffit at millenia.cars.aps.anl.gov
> Subject: Re: [Ifeffit] Ifeffit Digest, Vol 113, Issue 17
> Message-ID:
> <CAOJ5_YxOhbiN8zJfi_xG8+NSVuhnfTydyR==
> xc61Uov-CwdhMw at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> 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,
> <ifeffit-request at millenia.cars.aps.anl.gov>wrote:
>
> > Send Ifeffit mailing list submissions to
> > ifeffit at millenia.cars.aps.anl.gov
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> > To subscribe or unsubscribe via the World Wide Web, visit
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> > or, via email, send a message with subject or body 'help' to
> > ifeffit-request at millenia.cars.aps.anl.gov
> >
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> > When replying, please edit your Subject line so it is more specific
> > than "Re: Contents of Ifeffit digest..."
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> >
> > Today's Topics:
> >
> > 1. Re: Modeling Pt/C Catalyst Under WGS Conditions
> > (Anatoly I Frenkel)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Sat, 28 Jul 2012 01:02:23 +0000
> > From: Anatoly I Frenkel <afrenke2 at yu.edu>
> > To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> > Subject: Re: [Ifeffit] Modeling Pt/C Catalyst Under WGS Conditions
> > Message-ID: <98fc47e6-bd47-4c56-8fb2-3385fa7dbbbe at 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 <Branko.Zugic at tufts.edu>
> > To: "ifeffit at millenia.cars.aps.anl.gov" <
> ifeffit at 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 at tufts.edu<mailto:Branko.Zugic at tufts.edu>,
> > brankozugic at gmail.com<mailto:brankozugic at gmail.com><mailto:
> > brankozugic at gmail.com>
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>
>
>
> --
> PhD Candidate
> Tufts University, Chemical and Biological Engineering
> 4 Colby Street, Room 226
> Medford, MA 02155
> Ph: (O) 617 627 4338 (C) 508 414 8555
> Email: Branko.Zugic at tufts.edu, brankozugic at gmail.com
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