IDECAT WP3 Seminar - Max Planck Societypubman.mpdl.mpg.de/pubman/item/escidoc:737860:1/component/esci… · IDECAT WP3 Seminar Prag November 28,2006 ... extrapolation of Schram's

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IDECAT WP3 Seminar

Prag

November 28,2006

High pressure XPS: A tool for the investigation of heterogeneous catalytic processes

A. Knop-Gericke , D.Teschner, H. Bluhm, M. Hävecker

([email protected])

Fritz-Haber-Institut, Berlin, Department of Inorganic Chemistry

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• Very few methods can investigatethe solid-gas interfaceat high pressures- non-linerar optics (SFG, SHG)- scanning probe microscopies- X-ray diffraction

Why in situ XPS ?Why in situ XPS ?

15

10

5

-40 -20 0 20

temperature (ºC)

vapo

rpr e

s sur

e(t o

r r)w

ater Tm

• Photoelectron spectroscopy is very powerful⇒ Goal: XPS at pressures of at least 5 torr

• Many processes cannot beinvestigated in UHV:“Pressure Gap”- environmental chemistry- catalysis- corrosion- electrochemistry- biological samples

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Fundamental limit:elastic and inelasticscattering of electronsin the gas phase

Technical issues: - Differential pumping to keep analyzer in high vacuum- Sample preparation and control in a flow reactor

In situ XPS: obstaclesIn situ XPS: obstacles

30x10-21

25

20

15

10

5

0Io

niza

tion

cros

s se

ctio

n (m

2 )

101

102

103

104

105

106

Electron kinetic energy (eV)

in situSEM in situ

TEM

in situEXAFSin situ

XPS

O2 exp. data from Schram et al. (1965) extrapolation of Schram's data

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• Photons enterthrough a window

• Electrons and a gasjet escape throughan aperture tovacuum

In situ XPS: basic conceptIn situ XPS: basic concept

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H. Siegbahn et al., J. Electron Spectrosc. Relat. Phenom. , 319 (1973)2

• H. Siegbahn et al. (1973- )• M.W. Roberts et al. (1979)• M. Faubel et al. (1987) • M. Grunze et al. (1988)• P. Oelhafen (1995)

H. Siegbahn et al., J. Electron Spectrosc. Relat. Phenom. , 205 (1981)24

In situ XPS instruments: previous designsIn situ XPS instruments: previous designs

In situ XPS using differentially pumped electrostatic lensesIn situ XPS using differentially pumped electrostatic lenses

D.F. Ogletree, H. Bluhm, G. Lebedev, C.S. Fadley, Z. Hussain, M. Salmeron, Rev. Sci. Instrum. 73 (2002) 3872.

to pump to pump

X-rays from synchrotron

Gas phase composition canbe measured by XPS.gas phase signal: 1 torr·mm ~ a few monolayers

CloseClose--up of sampleup of sample--first aperture regionfirst aperture region

gas

z

d

hν

e-

p0

1.0

0.5

0.0-2 -1 0 1 2

z [d]

p/p 0

z=2 mm

d=1 mm

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In situ XPS systemIn situ XPS system

Experimental cellsupplied by gas lines (p0)

X-rays enter the cell at 55° incidence through an SiNx window(thickness ~ 1000 Å)

Analyzerinput lens

Focal point of analyzerinput lens

First differentialpumping stage (10-4p0)

Second differentialpumping stage (10-6p0)

Third differentialpumping stage (10-8p0)

Hemisphercalelectronanalyzer(10-9p0)

mass spectrometerand additional pumping

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IntroductionIntroduction

Literature carbon laydown selective hydrogenation“similar” catalysts different activity & selectivity

(structure sensitivity?)

Selectivity issue: what defines selectivity?

[ ]+ H2

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SummarySummary

1. Subsurface H : effective for alkene-to-alkane but also for alkyne-to-alkane transformation

2. Surface H : could be selective (spillover)3. Different reaction orders in the different selectivity regimes &

Abrupt changes between regimes4. C uptake is significantly more in the selective regime

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Reaction in the mbar p region (inReaction in the mbar p region (in--situ XPS)situ XPS)

-~2~20~5Selectivity

Pentane [%]

100~98~80~95Selectivity

Pentene [%]

<1~2.5~5~ 10Conversion

[%]

Pd(111)Pd foil3% Pd/Al2O35% Pd/CNT

+ H2

Recation conditions: C5/H2 = 1:9, 1 mbar, 358 K

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InIn--situ XPS: situ XPS: Pd 3d (hPd 3d (hνν: : 720 eV)720 eV)

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InIn--situ XPS: situ XPS: Pd 3d depth profilingPd 3d depth profiling

Not only adsorbate-induced surface core level

shift !

But on-top location!

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InIn--situ XPS: situ XPS: C1s (Switching off experiments)C1s (Switching off experiments)

1: reaction mix.

2: C5 off

3: H2 off

4: C5 gas-phase

Teschner et al.

J. Catal. 242 (2006) 26-37

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InIn--situ XPS: situ XPS: Pd 3d (Switching off experiments)Pd 3d (Switching off experiments)

1: reaction mix.

2: C5 off

3: H2 off

4: reaction; high T

523 K

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InIn--situ XPS: situ XPS: Pd vs. C depth profilingPd vs. C depth profiling

100 200 300 400 500 600 700 80020

25

30

35

40

45

50

55

60

65

70A

Palladium Inelastic Mean Free Path [Å]

Car

bon

Con

tent

[%]

Electron Kinetic Energy [eV]

Experiment: 358 K Model: 358 K Model: 3.5 ML Experiment: C5 off Model: C5 off

5.25 7.15 9.05 15.15

20

25

30

35

40

45

50

55

60

65

70

75100 200 300 400 500 600 700 800

22.3513.2510.25

Electron Kinetic Energy [eV]

Car

bon

cont

ent [

%]

Carbon Inelastic Mean Free Path [Å]

Epxeriment: 523K Model: 523K Model: 4.2 ML

7.25

B

0.3 nm

1.4 nm

14 nm

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SummarySummary



Abrupt changes between regimes4. C uptake is considerably more in the selective regime 5. Pd-C surface phase forms in the early stage of selective pentyne

hydrogenation & there is significant amount of subsurface Cbelow of it

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Model (during the reaction)Model (during the reaction)

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SummarySummary



Abrupt changes between regimes4. C uptake is considerably more in the selective regime 5. Pd-C surface phase forms during selective hydrogenation of

pentyne & there is significant amount of subsurface C below of it6. Dynamic behaviour of Pd-C and subsurface C

20M. Hävecker, Surface Analysis, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany

Outlook: In situ XPS / XASOutlook: In situ XPS / XASThe future at BESSYThe future at BESSY

Installation of a beamline exclusively used for in situ spectroscopy in the soft X-ray range

Installation of infrastructure optimized for these kind of experiments on site (e.g. chemical lab, gas supply, gas analytics)

ISISS:

Innovative Station for In Situ Spectroscopy A project of BESSY and the Dep. Inorganic Chemistry, Fritz-Haber-Institut

Later, further implementation of other in situ spectroscopy techniques: multi wavelength Raman, UV-Vis, fluorescence yield ?!

Start of user operation of the beamline: 2007



ISISS:

Sketch of laboratory: dr. heinekamp, Berlin, Germany



1,0E+09

1,0E+10

1,0E+11

0 200 400 600 800 1000 1200 1400

Photon Energy / eV

flux

(pho

t./s/

0.1A

/0.1

%B

W)

1200 l/mm, 80 μm

1200 l/mm, 20 μm

600 l/mm, 80 μm

600 l/mm, 20 μm

1000

3000

5000

7000

9000

0 200 400 600 800 1000 1200 1400

Photon Energy / eV

Res

olut

ion

(E/d

E)

1200 l/mm, 80 μm

1200 l/mm, 20 μm600 l/mm, 20 μm600 l/mm, 80 μm











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Thanks to:Thanks to:

• Detre Teschner, Elaine Vass, Michael Hävecker, EvgueniKleimenov,,Spiros Zafeiratos, Péter Schnörch, Hermann Sauer, Robert Schlögl (FHI, Dept. AC)

• Mounir Chamam, Attila Wootsch (Institute of Isotops, Budapest)

• Arran S. Canning, Jonathan J. Gamman, S. David Jackson (Glasgow University)

• James McGregor, Lynn F. Gladden (Cambrigde University)

• Fred Senf, Rolf Follath, Walter Braun, Jens Blume, Jan Schmidt (BESSY)

Documents

IDECAT WP3 Seminar - Max Planck Societypubman.mpdl.mpg.de/pubman/item/escidoc:737860:1/component/esci… · IDECAT WP3 Seminar Prag November 28,2006 ... extrapolation of Schram's