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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)
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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)
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
-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
heating: RT 400°Ccooling: 400°C RT
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
)
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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
heating: RT 400°Ccooling: 400°C RT
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
-120
-100
-80
-60
-40
-20
0heating cooling heating cooling
Changes in NEXAFS:Changes in NEXAFS:Resonance PositionResonance Position
rel. Position of V6 before first heating cycle =! 0
heating: RT 400°Ccooling: 400°C RT
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
0,75
0,8
0,85
0,9
0,95
1
rel. Intensity of V5 before first heating cycle =! 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
Comparison:Comparison:Catalysts of different performanceCatalysts of different performance
heat.: RT 400°Ccool.: 400°C RT
higheractivity
norm
. Inten
sity CAT62: high activityCAT63: low activity
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
11,11,21,31,41,51,61,71,8
rel. Intensity of V6 before first heating cycle =! 1
Comparison:Comparison:Catalysts of different performanceCatalysts of different performance
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
heat.: RT 400°Ccool.: 400°C RT
CAT62: high activityCAT63: low activity
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
-120
-100
-80
-60
-40
-20
0
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
Comparison:Comparison:Catalysts of different performanceCatalysts of different performance
higheractivity
rel. Position
(meV
)
heat.: RT 400°Ccool.: 400°C RT
CAT62: high activityCAT63: low activity
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
Comparison:Comparison:Catalysts of different performanceCatalysts of different performance
-180-160-140-120-100-80-60-40-20
0
rel. Position of V6 before first heating cycle =! 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
heat.: RT 400°Ccool.: 400°C RT
CAT62: high activityCAT63: low activity
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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???
M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany
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