robert a. schoonheydt center for surface chemistry and catalysis k.u. leuven
DESCRIPTION
ULTRAVIOLET-VISIBLE-NEAR INFRARED (UV-VIS-NIR) SPECTROSCOPY ELECTRON PARAMAGNETIC RESONANCE (EPR) or ELECTRON SPIN RESONANCE (ESR) OF ZEOLITES. Robert A. SCHOONHEYDT Center for Surface Chemistry and Catalysis K.U. Leuven Kasteelpark Arenberg 23, 3001 Leuven Belgium - PowerPoint PPT PresentationTRANSCRIPT
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Robert A. SCHOONHEYDT
Center for Surface Chemistry and CatalysisK.U. LeuvenKasteelpark Arenberg 23, 3001 LeuvenBelgium
•ULTRAVIOLET-VISIBLE-NEAR INFRARED (UV-VIS-NIR) SPECTROSCOPY
•ELECTRON PARAMAGNETIC RESONANCE (EPR) or ELECTRON SPIN RESONANCE (ESR)
OF ZEOLITES
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OUTLINE
1. Principles of UV-VIS-NIR- physical basis- methodology
2. In-situ UV-VIS3. Optical and fluorescence microscopies4. Principles of EPR
- physical basis- methodology
5. In-situ EPR6. Pulse EPR7. Coordination of transition metal ions (TMI) 8. Conclusions
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UV-VIS-NIR
Wavelength nm 200 375 750 2500
Wavenumber cm-1 50000 26664 13300 4000
Frequency Hz 1.5x1015 8x1014 4x1014 1.2x1014
UV VISIBLE NIR
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What do we measure ?
Molecules: unsaturated
* and n * transitionsEnergy level diagramme
Bonding
Bonding
Nonbonding
Antibonding
Antibonding
*
π*
π
π
n
*
*
π π
*
n
π *
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Transitions Metal Ions
d – d transitionsLigand- to Metal Charge Transfer(LMCT)
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Transitions Metal Ions
d – d transitionsMetal - to Ligand Charge Transfer(MLCT)example: [Cr(benzene)2]+
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UV - VIS - NIR: Methodology
Powdered samples Diffuse Reflectance Spectroscopy (DRS)Principle
x
I
JI + I
J + J
I0
x
J0
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Ideal Case: Kubelka – Munck formula
kc
S
K
R
RRF
2
1 2
K : Kubelka-Munck absorption coefficientS : Kubelka-Munck scattering coefficient
scattering intensity from infinitely thick sample
scattering intensity from infinitely thick white standardR∞ =
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Conditions for use of K M-formula
•diffuse monochromatic irradiation•isotropic scattering•infinite sample thickness•low concentration of absorbing centers•uniform distribution of absorbing centers•absence of fluorescence
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UV – VIS – NIR: instrumentation
•Every compagny has a UV-VIS-NIR spectrophotometer withtwo sources ( Nerst glower, D2 lamp) and two detectors (PbS, PM).
•Integration sphere for DRS
•White standards: MgO, BaSO4, HALON.
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IN – SITU UV-VIS-NIR
Most sensitive region: VISIBLE low background sensitive detection: PM
Praying Mantis Optical fibre technology
Gas inlet
Gas outlet
h
Optical fiber
GCComputer
Multi-channeldetector
UV-vis sourceOven
Reactor
Catalyst bed
Quartz wool
High-temp. probeFlow in
Flow out
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IN – SITU UV-VIS-NIR
Examples: d d (pseudo)tetrahedral Co2+
O Cr6+ charge transfer (chromate, dichromate)
O Cu2+ bis(µ-oxo)dicopper
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AlPO4-5AFI
OO
O OO OAl AlP
OO OO
-1 +1 -1
OO
O OO OAlP
OO OO
-2 +1 -1
Co2+Isomorphoussubstitution
Co
Microporous crystalline metal-containingAluminiumphosphates:isomorphous substitution
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500 1000 1500 2000 2500
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
24u
16u
0u
25°c
synthesis CoAPO-5
abso
rban
ce
wavelength
Abs
orba
nce
Wavelength (nm)
CoAPO-5: in situ synthesis
Synthesis time
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CoAPO-5 synthesis: spectra at RT
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Chromate reduction with CO in zeolite Y
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10000 20000 30000 40000 50000
CZ-31-0.16 CZ-31-0.34 CZ-31-0.58
abso
rptio
n (a
.u.)
wavenumber (cm-1)
bis( µ-oxo )dicopper in ZSM-5
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OPTICAL and FLUORESCENCE MICROSCOPIES
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Intergrowth structure of ZSM-5
Accessibility?
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Applications
Oligomerization of furfurylalcohol in ZSM-5 and mordenite
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Applications
Oligomerization of styrene in ZSM-5
R R
R
R
R R
R R
R R
H++
A
Trimetric ologomers
E
+
+ +
B
B D
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oligomerization of styrene: absorption spectra
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Decomposition of template molecules in CrAPO-5
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Decomposition of template molecules and intergrowth structures
CrAPO-5 SAPO-34 SAPO-5 ZSM-5
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ELECTRON PARAMAGNETIC RESONANCE
magnetic moment of the unpaired elelctron
= dimensionless spin angular momentum vector of the electronS2 = s(s+1) s = ½SZ =ms ms = 1/2, -1/2
= Borhmagneton
g, spectroscopic splitting factor = 2.0023ħ = h/2πγ = gyromagnetic ratio
S
zShzSgzµ
ShSgµ
2
2
124102741,92
JTxem
he
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ZEEMAN INTERACTIONZEEMAN INTERACTION
EZ = -µZB0 = gβB0ms
ms = ½: 1/2g βB0
ms = -½: -1/2g βB0
Resonance condition: hν = E = gβB0
ms = 1/2
ms = - 1/2
E = gβB0
E
B0
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EPR: powder spectraEPR: powder spectra
All possible orientations of the spins Each orientation has its own resonance condition Spectra are superpositions of all those individual spectra
isotropic
axially symmetric
orthorhombic
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EPR: Measurement of g valuesEPR: Measurement of g values
measurement at constant frequency and varying magnetic field
g = = 7,145x10-9 ν/B0 to be measured with gaussmeter
to be read from microwave bridge
reference: DPPH gr = 2,0036 (diphenylpicrylhydrazine)
0B
Bgg r
r
Band name band range, GHz
L 1.5S 2.6-4C 4-6X 8.2-12.4K 18-26.5Q 33-50V 50-75W 75-100
0B
h
rrBgBgh
0
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Resonance cavities
EPR: METHODOLOGIES
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-Hyperfine interaction: unpaired electron-nuclear spin: I mI = I, I - 1,…..,- I each energy level of the electron is split according to m I
selection rule for EPR: ms = 1: mI = 0
- S > ½ more than one unpaired electron: ZERO FIELD SPLITTING
- QUADRUPOLAR INTERACTION: nuclear spins with I > 1/2
EPR: Spin Hamiltonian
-SPIN HAMILTONIAN
IPISDSIASBgSH .......
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EPR: Quantitative
)1(
)1(
SS
SS
g
g
I
INN rrr
rr
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In situ EPR
Set-up
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FeAPO-5
Example: calcination of FeAPO-5
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PULSE EPR
D. Goldfarb, Weizmann Institute, Israel
ESEEM: electron spin echo envelope modulation
ENDOR: electron nuclear double resonance
Examples:
1. Interaction of Cu2+ with Al nuclei in the zeolite lattice
2. Copper –histidine complexes in supercages of zeolite Y.
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Copper – histidine complexes in supercages of zeolite Y
gا gاا Aاا(mT) d – d (cm-1)
A 2.054 2.31 15.8 15200
B 2.068 2.25 18.3 15600
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TRANSITION METAL IONS IN ZEOLITES
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Coordination to lattice oxygens
Characteristics•Low coordination number
•Free coordination sites
•Low symmetry
Examples: Cu2+, Co2+
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Cu2+: DRS + EPR
ZSM-5 Zeolite A
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Zeolite g A/mT g A/mT
mordenite 2.327 15.42 2.062 1.49
ZSM 5 2.277 16.82 2.057 1.19
A, X, Y 2.387 12.20 2.069 1.34
Y, chabasite 2.336 15.85 2.070 1.93
d-d transitions/cm-1
mordenite 12500 13700 14800
ZSM 5
A, X, Y 10400 12300 14800
Y, chabasite 10800 12900 14800
Cu2+: Summary of EPR parameters and d – d transitions
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Coordination of Co2+ and Cu2+ to sixrings: LF or AOM
Fixed oxygens: Cu2+/Co2+ in the center of the six- ring on trigonal axis
Cu2+: doubly degenerate ground-state Jahn-Teller distorsion
Co2+: off-axial displacement by 0.078 – 0.104nm
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Coordination to six-rings in LTA and FAUCu2+
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Cu2+:orbital interactions between d(Cu2+) and p(0)
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T5 T11
T1 T4
O3T2 T8
O1
O2
O5
O4
O6
T7
2.02
2.13
2.90
3.211.98
3.09
2.12
2.41
Al
AlAl
Al
3.602.90
2.06
3.40
3.24
2.88
1.98
1.96
Al
Al
3.042.42
2.07
3.142.46
3.19
1.94
2.00
Al
2.00
3.26
2.06
2.08
3.15
2.00
2.27 3.46
Al
2.16
3.41
2.92
2.32
1.98
3.40
2.62
1.98
0 1 2
binding energyg-factors
-6512.29 2.10 2.05
-6382.29 2.09 2.05
2' 3 4
-6352.33 2.10 2.05
-4982.31 2.08 2.07
-4812.33 2.08 2.07
Cu2+in ZSM-5: α sites with zero, one and two Al’s
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O1
O2
O3
O4
O5
O6T5
T4
T7T11
T10
T1
Al Al
3.53
1.89
3.50
1.961.89
1.98Al
Al
3.55
1.87
3.36
2.08
2.11
1.88
Al
Al
3.62
2.14
1.98
1.87
1.93
3.24
Al
1.93
3.37
1.95
2.07
3.45
1.87
Al
3.57
2.09
1.96 2.06
1.86
3.22
Al
2.42
3.46
1.96
3.15 2.04
1.79
HO
4.10
0 1 2 3
binding energyg-factors
-7152.23 2.07 2.04
-6772.25 2.10 2.03
-6832.24 2.07 2.04
4 5
-5322.24 2.07 2.04
-5142.25 2.09 2.04
Cu2+in ZSM-5: β sites with zero, one and two Al’s
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T7
T12
T7
T11
T12
T10
O1
O2
O3
O5
O6
T10O4
T11
1.95 1.95
1.96 1.96
3.41
3.44
Al AlAl
Al
1.96
1.91
3.37
1.93
2.09
3.38
Al
Al
1.91
1.96
3.27
2.05
2.17
3.00
Al Al
3.29
1.98 2.10
1.972.06
3.32
Al
1.93
3.30
1.94
2.02
2.04
3.31
Al
1.90
2.08
3.28
2.07
3.09
2.02
-5052.28 2.08 2.05
-5232.27 2.06 2.06
-6562.29 2.07 2.06
654
-6622.27 2.07 2.06
-6802.26 2.07 2.05
-6982.25 2.06 2.06
binding energyg-factors
3210
Cu2+in ZSM-5: γ sites with zero, one and two Al’s
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T2
T1
T10
T6
T9 Al
2.03 2.09
1.923.08
1.92
Al
2.01 1.92
2.93 1.95
2.05
OH
1.97
1.99
3.51
4.43
3.57
Al
1.78
0 1 2
binding energyg-factors
-4822.27 2.09 2.05
-4832.25 2.08 2.05
Cu2+in ZSM-5: δ sites with zero, one and two Al’s
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Cu2+in Zeolite: O Cu2+ charge transfer
ν (cm-1) = 30,000[χopt(0)-χopt(Cu2+)]
cm-1/1
000
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DRS spectrum of Co2+in Zeolite A
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DRS spectrum of Co2+in Zeolite Y and its decomposition
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DRS spectrum of Co2+in LTA and FAU:visible region
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Co2+in FAU: interpretation
LF: trigonal Co2+
T: pseudo-tetrahedral Co2+ in site I’
HF: pseudo-octahedral Co2+ in site I
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Coordination sites in pentosil zeolites(ZSM-5, MOR, FER)
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Co2+ spectra in pentasil zeolites(ZSM-5, MOR, FER)
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CONCLUSIONS
1. Significant technical advancementDRS in situ single crystalEPR wide range of resonance frequencies
in situ pulse
2. Coordination of transition metal ions maximize coordination number site distortion number of Al tetrahedra
3. In situUV-VIS: catalyst activation: chromate Cr3+
active site: bis(µ-oxo)dicopper isomorphous substitution: Co2+
EPR: isomorphous substitution of Fe3+
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CONCLUSIONS
4. Pulse EPR:- interaction TMI – Al in lattice- coordination chemistry of Cr(histidine)x in supercages- In situ techniques and pulse EPR give nice results in well-chosen problems.- Specialists are necessary; these are not routine measurements
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Thanks to
Collaborators:(D. Packet, S. De Tavernier, M. Uytterhoeven, B. Weckhuysen, A. Verberckmoes, M. Groothaert,H. Leeman)
Collaborations:K. Pierloot and A. CeulemansK. Klier
Financial support:Concerted Research ActionFund for Scientific Research