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QEXAFS at the superXAS beamline

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IXS group

Senior scientists:M. HarfoucheM. Nachtegaal

Ph.D. students:E.M. AlayonJ. Frommer (ETHZ)??

Technician:??

SNF Postdoc:E. Kleimenov

SLS support:P. Jaloscha Controls (X02DA, X07LA)B. Meyer Technician (X05LA)M. Williman Electrical Engineer(X05LA)C. Frieh Electrical Engineer (X07LA)

ACCEL instruments:Markus Schwoerer-Boehning (beamline construction)Riccardo Signorato (ray tracing)

Acknowledgements

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M-XASFEMTO

superXAS

PHOENIX replaces LUCIA

PolLux

nanoXAS2009

Swiss Light Source

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superXAS4.5-40keV

microXAS4-23keV

PHOENIX0.4-8keV

PolLux0.2-1.1keV

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Super? … Swiss Light Source

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Brilliance at SLS Super bend source, (2.9 Tesla)

Flux at SLS Super bend source, (2.9 Tesla)

XAS at a `XAS at a `superbendsuperbend` ` portport

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Beamline layout

• First mirror: vertically collimating mirror (Pt, Rh, bare Si) placed in FE• Fixed exit DCM, with Si (111) and Si (311)• QEXAFS DCM• Second mirror: toroidal mirror (Pt, Rh)

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Energy resolution

7.8559E+11 12

7.8253E+11 11.5

7.7096E+11 11

7.5566E+11 10.5

6.8859E+11 10

6.8849E+11 9.5

6.2625E+11 9

5.6253E+11 8.5

4.7324E+11 8

3.8716E+11 7.5

2.9711E+11 7

2.0941E+11 6.5

1.3472E+11 6

With calibrated Si diode- Rh mirror coatings- Moved off the rocking curve- not corrected for 50 cm air path

Measured flux

Performance of the beamline

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Timeline superXASDesign study: January-July 2005Contract ACCEL January 2006First light: April 2007Commissioning October-December 2007User operation: since January 2008

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Monochromator for time resolved studies

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Raw absorption data of the L-edges of a platinum foil, 2 Hz oscillation frequency

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5 Hz oscillation frequency

Cu K-edge

measured at 2 Hz compared to the result using a conventional monochromator

Fe K-edge

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Quick EXAFS data aquisition

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Performance of the beamline

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CO oxidation: 2CO + O2 2CO2

From the 2007 Nobel prize acceptance speech of Ertl

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What do we know from surface science studies

Two activity regimes: -Low activity: metallic surface, poisoned with CO-High activity: surface reconstruction, chemisorbed O, oxidized surface, still metalReaction mechanism: Langmuir-Hinshelwood

In the real world: - Technical catalysts are nano-sized and on support materials gap- Technical catalysts operate under atmospheric pressure conditions pressure gap

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CO oxidation on supported Pt nanoparticles: closing the pressure and materials gap

Rate of oxidation of carbon monoxide over 2 wt.-% Pt/Al2O3 during heating at oxygen to carbon monoxide ratios of 1 (green), 2 (blue), and 5 (pink).

HERFD, ID26 (ESRF)Ignition/extinction

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11580 11600 11620

0.9

1.2

1.5

Energy/eV

(a)

normalized absorption

470 471 472 473 474 47540

50

60

70

80

90

100

Temperature/ K

(b)

CO Coversion %

CO oxidation on supported Pt nanoparticles: Quick-EXAFS

PtO2Pt metal

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CO oxidation on supported Pt nanoparticles:Reaction mechanism

J. Singh, E.M. Alayon, M. Tromp, O.V. Safonova, P. Glatzel, M. Nachtegaal, R. Frahm, J. A. van Bokhoven (2008) Angewandte Chemie – Int. Ed. 47, 9260-9264

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What is the role of the support?

Pt/TiO2 (pink),s-Pt/Al2O3 (black), b-Pt/Al2O3 (red), and Pt/SiO2 (green)

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What is the role of the support?

Pt/Al2O3Ignition at 226oC

Pt/TiO2Ignition at 188oC

Pt/SiO2Ignition at 299oC

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What is the structure of the oxide (Pt/Al2O3)?

Path CN DWP R(Å) ΔEo (eV) Goodness of fit GasPt-Pt 5.5 0.004 2.72 1.7 5.0 HePt-Pt 5.7 0.005 2.77 0.5 14.9 CO/O2Pt-O 1.3 0.002 1.96 3.6 36.7 CO/O2Pt-Pt 5.2 0.005 2.72

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Proposed reaction scheme

E.M. Alayon, J.Sing, M. Nachtegaal, M. Harfouche, J. A. van Bokhoven (2009) Journal of Catalysis, in press

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Current upgrades

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3D XAS

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X-ray emission spectroscopy

High energy resolution XAS, X-ray emission spectroscopy, hard X-ray resonance inelastic X-ray scattering, site selective EXAFS

- Fluorescence detection with sub eV resolution- Commissioning in April this year

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superXAS

- Energy range: 4.5-40 keV, ΔE/E = 2.10-4

- Flux: ~1012 photons/second (super cooled bending magnet)

- Variable spot size: 10 x 2 mm, 90 x 90 μm

- Ge-13 element detector, 25 cm harmonic rejection mirror

- Quick scanning monochromator (max speed 12 Hz), Quick scanning mode with DCM (few seconds)

- Gas infrastructure (gas warning system, fume hood, several in situ cells, laboratory, glove box, MS, mass flow controllers)

- In situ X-ray emission spectroscopy

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Thank you!