Robert A. SCHOONHEYDT

Center for Surface Chemistry and CatalysisK.U. LeuvenKasteelpark Arenberg 23, 3001 LeuvenBelgium

Robert.schoonheydt@biw.kuleuven.ac.be

•ULTRAVIOLET-VISIBLE-NEAR INFRARED (UV-VIS-NIR) SPECTROSCOPY

•ELECTRON PARAMAGNETIC RESONANCE (EPR) or ELECTRON SPIN RESONANCE (ESR)

OF ZEOLITES

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

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

What do we measure ?

Molecules: unsaturated

* and n * transitionsEnergy level diagramme

Bonding

Bonding

Nonbonding

Antibonding

Antibonding

*

π*

π

π

n

*

*

π π

*

n

π *

Transitions Metal Ions

d – d transitionsLigand- to Metal Charge Transfer(LMCT)

Transitions Metal Ions

d – d transitionsMetal - to Ligand Charge Transfer(MLCT)example: [Cr(benzene)2]+

UV - VIS - NIR: Methodology

Powdered samples Diffuse Reflectance Spectroscopy (DRS)Principle

x

I

JI + I

J + J

I0

x

J0

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∞ =

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

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.

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

IN – SITU UV-VIS-NIR

Examples: d d (pseudo)tetrahedral Co2+

O Cr6+ charge transfer (chromate, dichromate)

O Cu2+ bis(µ-oxo)dicopper

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

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

CoAPO-5 synthesis: spectra at RT

Chromate reduction with CO in zeolite Y

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

OPTICAL and FLUORESCENCE MICROSCOPIES

Intergrowth structure of ZSM-5

Accessibility?

Applications

Oligomerization of furfurylalcohol in ZSM-5 and mordenite

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

oligomerization of styrene: absorption spectra

Decomposition of template molecules in CrAPO-5

Decomposition of template molecules and intergrowth structures

CrAPO-5 SAPO-34 SAPO-5 ZSM-5

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

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

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

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

Resonance cavities

EPR: METHODOLOGIES

-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 .......

EPR: Quantitative

)1(

)1(

SS

SS

g

g

I

INN rrr

rr

In situ EPR

Set-up

FeAPO-5

Example: calcination of FeAPO-5

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.

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

TRANSITION METAL IONS IN ZEOLITES

Coordination to lattice oxygens

Characteristics•Low coordination number

•Free coordination sites

•Low symmetry

Examples: Cu2+, Co2+

Cu2+: DRS + EPR

ZSM-5 Zeolite A

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

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

Coordination to six-rings in LTA and FAUCu2+

Cu2+:orbital interactions between d(Cu2+) and p(0)

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

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

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

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

Cu2+in Zeolite: O Cu2+ charge transfer

ν (cm-1) = 30,000[χopt(0)-χopt(Cu2+)]

cm-1/1

000

DRS spectrum of Co2+in Zeolite A

DRS spectrum of Co2+in Zeolite Y and its decomposition

DRS spectrum of Co2+in LTA and FAU:visible region

Co2+in FAU: interpretation

LF: trigonal Co2+

T: pseudo-tetrahedral Co2+ in site I’

HF: pseudo-octahedral Co2+ in site I

Coordination sites in pentosil zeolites(ZSM-5, MOR, FER)

Co2+ spectra in pentasil zeolites(ZSM-5, MOR, FER)

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+

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

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