In-situ Characterisation of vanadium-phosphorus-oxide (VPO) catalysts for n-butane oxidation by...

In-situ Characterisation of In-situ Characterisation of vanadium-phosphorus-oxide (VPO) catalysts for n-butane vanadium-phosphorus-oxide (VPO) catalysts for n-butane

oxidation by applying X-ray absorption spectroscopyoxidation by applying X-ray absorption spectroscopy

M. HäveckerM. Hävecker, R. W. Mayer, A. Knop-Gericke, H. Bluhm, R. Schlögl, R. W. Mayer, A. Knop-Gericke, H. Bluhm, R. Schlögl

Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany

DFG Schwerpunktprogramm Workshop, Blankensee, 25.-26. April 2002

M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany

n-Butane Oxidation to MAn-Butane Oxidation to MAby Vanadium Phosphorus Catalystsby Vanadium Phosphorus Catalysts

+ 3,5 O2 + 4 H2O

1,5 Vol% air

C4H10 + 6,5 O2 4 CO2 + 5 H2O

C4H10 + 4,5 O2 4 CO + 5 H2O

VPO

400 °C, 1 bar O

O

O

Maleic Anhydride (MA)


Experimental TechniqueExperimental Technique

Near

Edge

X-ray

Absorption

Fine

Structure

X-ray absorption spectroscopy

local process related to site- and symmetry selected DOS

A. Knop-Gericke et al., Nucl. Instr. Meth. A 406 (1998) 311M. Hävecker et al., Angew. Chem. 110 (1998) 2049; Int. Ed. 37 (1998) 206

The Light Source: Synchrotron RadiationThe Light Source: Synchrotron Radiation


Support for dynamic surface conceptSupport for dynamic surface concept

Comparing VPO catalysts of different catalytic performance

Comparing VPO catalysts of different catalytic performance

Changes of NEXAFS under n-butane oxidation conditions

Changes of NEXAFS under n-butane oxidation conditions

BerlinerElektronenspeicherringgesell-schaft für Synchrotronstrahlung

(Photographs: Luftbild u. Pressefoto R.Grahn)


V L- and O K-absorption edgeV L- and O K-absorption edge

510 520 530 540 550

Photon Energy / eV

0

1

2

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L + O K-edges Vac, RT

VPO

V2O5

V L-edges O K-edge

V L3V L2

O-V

O-PV L3


The VPO V LThe VPO V L33-NEXAFS-NEXAFS

512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge

V1

V2

V3

V5

V4 V6

V7

Analysis of spectral shape by unconstrained least squares fit

M. Abbate et al., J. Electron Spectrosc. Rel. Phenom., 62 (1993) 185M. Hävecker et al., J. Electron Spectrosc. Rel. Phenom., in press

V valenceV valence

Details of the local chemical bonding

Details of the local chemical bonding

Local geometric structure

Local geometric structure


Catalytic Activity Catalytic Activity

0 1000 2000 3000 4000 5000

cycles

0

10

20

30

PT

R-M

S R

espo

nse

m/e

=99

100

200

300

400

Tem

pera

ture

/ °

C

Product Analysis by Online Proton Transfer Reaction Mass Spectrometry (PTR-MS) I(m/e=99) : Maleic Anhydride (MA)

Desorption PeakDesorption Peak

const. MA Yieldconst. MA Yield

flow of 1.2 vol % C4H10 / 20 vol % O2 / 78.8 % He

flow of 1.2 vol % C4H10 / 20 vol % O2 / 78.8 % He

Ptot = 2 mbarPtot = 2 mbar

RT to 400 °CRT to 400 °C


0,300

0,350

0,400

0,450

0,500

0,550

rel.

sp

ec

tra

l In

ten

sit

y

Spectrum Number

Changes in NEXAFSChanges in NEXAFSwhile heatingwhile heating

PTR-MS Response MA

Decrease w

hile activeD

ecrease while active

Relative spectral Intensity of V5 at V L3-edge

512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge

V5


0,15

0,2

0,25

0,3

0,35

0,4

Re

so

na

nc

e P

os

itio

n (

+5

17

eV

)

PTR-MS Response MA

Shift to low

er Ene rgy

Shift to lo w

er Ene rgy

Spectrum Number

Energy Position of V5 at V L3-edge

512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge

Changes in NEXAFSChanges in NEXAFSwhile heatingwhile heating


Changes in NEXAFS:Changes in NEXAFS:Relative spectral IntensityRelative spectral Intensity

0,75

0,8

0,85

0,9

0,95

1

heating cooling heating cooling

rel. Intensity of V5

512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge

heating: RT 400°Ccooling: 400°C RT

before first heating cycle =! 1

norm

. Inten

sity

V5


-80

-60

-40

-20

0heating cooling heating cooling

Changes in NEXAFS:Changes in NEXAFS:Resonance PositionResonance Position

rel. Position of V5 before first heating cycle =! 0


512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge

rel. Position

(meV

)


1

1,2

1,4

1,6

1,8

heating cooling heating cooling

Changes in NEXAFS:Changes in NEXAFS:Relative spectral IntensityRelative spectral Intensity

rel. Intensity of V6 before first heating cycle =! 1


norm

. Inten

sity

512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge

V6


-120

-100

-80

-60

-40

-20

0heating cooling heating cooling

Changes in NEXAFS:Changes in NEXAFS:Resonance PositionResonance Position



rel. Position

(meV

)

512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge


0,00

0,10

0,20

0,30

0,40

0,50

rel.

spec

tral

Inte

nsi

ty

V1 V2 V3 V4 V5 V6 V7

CAT63 RT

CAT62 RT

Comparison:Comparison:Catalysts of different performanceCatalysts of different performance

Investigation of 2 catalysts of different intrinsic catalytic activity

higher catalyticactivity

YMA (CAT62) = 1.5 x YMA (CAT63) J. A. Lopez Sanchez et al., to be published


0,75

0,8

0,85

0,9

0,95

1


512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge


heat.: RT 400°Ccool.: 400°C RT

higheractivity

norm

. Inten

sity CAT62: high activityCAT63: low activity


11,11,21,31,41,51,61,71,8



higheractivity

norm

. Inten

sity

512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge


CAT62: high activityCAT63: low activity


-120

-100

-80

-60

-40

-20

0


512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge


higheractivity

rel. Position

(meV

)





-180-160-140-120-100-80-60-40-20

0


higheractivity

rel. Position

(meV

)

512 514 516 518 520

Photon Energy / eV

0

2

4

6

Tot

al E

lect

ron

Yie

ld (

norm

. u.

) V L3-edge




SummarySummary

NEXAFS changes, at least partially reversible under n-butane oxidation conditions (resonance intensity, resonance position)

NEXAFS changes, at least partially reversible under n-butane oxidation conditions (resonance intensity, resonance position)

Observation of dynamic rearrangements (electronic and/or geometric structure) of VPO catalyst under n-butane oxidation conditions

Observation of dynamic rearrangements (electronic and/or geometric structure) of VPO catalyst under n-butane oxidation conditions

in line with: N.-Y. Topsøe et al., Cat. Lett. 76 (2001) 11 (vanadia DeNOx catalysts)in line with: N.-Y. Topsøe et al., Cat. Lett. 76 (2001) 11 (vanadia DeNOx catalysts)

Support for dynamic surface conceptSupport for dynamic surface concept

J.- C. Volta., Catal. Today, 32 (1996) 29J.- C. Volta., Catal. Today, 32 (1996) 29

Do structural rearrangements determine the catalytic activity?Do structural rearrangements determine the catalytic activity???


Thanks !Thanks !

The University of Wales:

G. J. Hutchings

J. A. Lopez-Sanchez

The University of Wales:

G. J. Hutchings

J. A. Lopez-Sanchez

BESSY staffBESSY staff

FHI

Evgueni Kleimenov

Detre Teschner

FHI

Evgueni Kleimenov

Detre Teschner

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