Transcript Document 7382297

Solid-state NMR studies on
microporous and mesoporous materials
concerning their structure, acidity and
catalytic activity
 1H MAS NMR spectra including TRAPDOR
 29Si MAS NMR
 27Al 3QMAS NMR
 27Al MAS NMR
 1H MAS NMR in the range from 160 K to 790 K
Dieter Freude, Institut für Experimentelle Physik I der Universität Leipzig
METU-Center Workshop on Solid State NMR, 1 November 2007
1H
MAS NMR spectra, TRAPDOR
Without and with dipolar dephasing by 27Al high power irradiation and difference spectra are
shown from the top to the bottom. The spectra show signals of SiOH groups at framework
defects, SiOHAl bridging hydroxyl groups, AlOH group.
2.2 ppm
4.2 ppm
2.9 ppm
2.2 ppm
H-ZSM-5
activated
at 550 °C
1.7 ppm
2.9 ppm
1.7 ppm
H-ZSM-5
activated 4.2 ppm
at 900 °C
without dephasing
with dephasing
4.2 ppm
2.9 ppm
2.9 ppm
4.2 ppm
difference spectra
10
8
6
4
2
 / ppm
0
2
4
10
8
6
4
2
 / ppm
0
2 4
1H
MAS NMR of porous materials
Disturbed bridging OH groups in zeolite
H-ZSM-5 and H-Beta
SiOH
Bridging OH groups in small channels
and cages of zeolites
SiOHAl
Bridging OH groups in large channels
and cages of zeolites
SiOHAl
Cation OH groups located in sodalite
cages of zeolite Y and in channels of
ZSM-5 involved in hydrogen bonds
CaOH, AlOH,
LaOH
OH groups bonded to extra-framework aluminium
species located in cavities or channels involved in
hydrogen bonds
AlOH
Silanol group at the externel surface
or at lattice defects
SiOH
Metal or cation OH groups in large cavities
or at the outer surface of particles
7
6
5
4
3
MeOH
2
ppm
1
0




29Si
MAS NMR spectrum of silicalite-1
SiO2 framework consisting of 24 crystallographic different silicon sites per unit cell (Fyfe 1987).
29Si
MAS NMR
Q0
alkali and
alkaline earth silicates
Q1
Q2
Q3
Q4
Q3
Si(3Si, 1OH)
Si(4 Al)
Si(3 Al)
Q4
aluminosilicate-type
zeolites
Si(2 Al)
Si(1 Al)
Si(0 Al)
Q

zincosilicate-type
zeolites
VP-7, VPI-9
Si(2 Zn)
4
Si(1 Zn)



ppm




27Al
3QMAS NMR study of AlPO4-14
1/ ppm
0
position 5
10
20
position 3
30
position 1
40
position 2
2/ ppm 40
30
20
10
0
AlPO4-14, 27Al 3QMAS spectrum (split-t1-whole-echo, DFS pulse) measured at 17.6 T with a
rotation frequency of 30 kHz.
The parameters CS, iso = 1.3 ppm, Cqcc = 2.57 MHz, h = 0.7 for aluminum nuclei at position 1, CS, iso = 42.9 ppm,
Cqcc = 1.74 MHz, h = 0.63, for aluminum nuclei at position 2, CS, iso = 43.5 ppm, Cqcc = 4.08 MHz, h = 0.82,
for aluminum nuclei at position 3, CS, iso = 27.1 ppm, Cqcc = 5.58 MHz, h = 0.97, for aluminum nuclei at position 5,
CS, iso = 1.3 ppm, Cqcc = 2.57 MHz, h = 0.7 were taken from Fernandez et al.
27Al
MAS NMR spectra
of a hydrothermally treated zeolite ZSM-5
four-fold
coordinated
five-fold
coordinated
six-fold
coordinated
nL = 195 MHz
nRot = 15 kHz
nL = 130 MHz
nRot = 10 kHz
100
80
60
40
20
 / ppm
0
20
40
60
A signal narrowing by MQMAS or DOR is useless, if the line
broadening is dominated by distributions of the chemical shifts.
27Al
MAS NMR
6-fold
coordinated
aluminophosphates
aluminoborates
aluminates
aluminosilicates
4-fold
coordinated
5-fold
coordinated
aluminophosphates
aluminoborates
aluminates
aluminosilicates
aluminophosphates
aluminoborates
aluminates
3-fold
coord.
aluminosilicates
aluminosilicates
120
110 100
90
80
70
60
50
ppm
40
30
20
10
0
10
20
Mobility of the Brønsted sites
and hydrogen exchange in zeolites
H
H one-site jumps around
one aluminum atom
O
O
O
O
O
Al
Si
Si
O O
O O
O O
H H
multiple-site jumps
along several
aluminum atoms
O
NH4+
O
Al
H
O O
O
H
O
O
O
Al
Si
Si
Al
O O
O O
O O
O O
Proton mobility of bridging hydroxyl groups in zeolites H-Y and H-ZSM-5 can be monitored in
the temperature range from 160 to 790 K. The full width at half maximum of the 1H MAS NMR
spectrum narrows by a factor of 24 for zeolite H-ZSM-5 and a factor of 55 for zeolite 85 H-Y.
Activation energies in the range 20-80 kJ mol have been determined.
Narrowing onset and correlation time
fwhm of the sideband envelope / kHz
40 °C
10
20
120°C
17 kHz
10
n = nrigid/2
3,2 kHz
1
n = nrigid/2
2H
1H
MAS NMR, zeolite H-Y, loaded
with mit 0.6 NH3 per cavity
MAS NMR, deuterated
zeolite H-ZSM-5, loaded with
0.33 NH3 per crossing
1
0,1
1,5
2,0
2,5
3,0
3,5 4,0 4,5
1000 T 1/ K1
5,0
5,5
2,5
3,0
3,5
4,0
4,5
5,0
1
1
1000 T  / K
5,5
6,0
The correlation time corresponds to the mean residence time of an ammonium ion at an
oxygen ring of the framework.
tc 
1
1 n rigid
NMR, H-Y: at50 °C tc=5 µs
1H NMR, H-Y: at 40 °C t =20 µs
c
2H NMR, H-ZSM-5: at 120 °C t =3,8 µs
c
2H
1D 1H EXSY (exchange spectroscopy)
p/2
p/2
t1
p/2
tm
FID
t2
time
0
EXSY pulse sequence
Evolution time t1 = 1/4 Dn .
Dn denotes the frequency difference of the exchanging species.
MAS frequency should be a multiple of Dn
Two series of measurements should be performed at each temperature:
Offset Dn right of the right signal and offset Dn left of the left signal.
Result of the EXSY experiment
Intensity
ammonium ions
Stack plot of the spectra of zeolite
H-Y loaded with 0.35 ammonia
molecules per cavity. Mixing times
are between tm = 3 ms and15 s.
OH
97 °C
 / ppm 10
0
2
4
6
8
10
12
0
2
4
6
8
10
12
0
Intensities of the signals of ammonium
ions and OH groups for zeolite H-Y
loaded with 1.5 ammonia molecules per
cavity. Measured at 87 °C in the field of
9,4 T. The figure on the top and bottom
correspond to offset on the left hand side
and right hand side of the signals,
respectively.
mixing time tm / s
Basis of the data processing
diagonal peaks
I AA (t m ) 

1 











1

exp



D
t

1

exp



D
t




m
m  M A0

2 
D
D



1 



IBB (t m )   1  exp-   D t m    1   exp   D tm  MB0
2 
D
D


cross peaks
1
1
I AB (t m )  IBA (t m )  exp σ  D t m  exp σ  D t m M A 0
2
t BD
1
exp σ  D tm  exp σ  D tm MB0 1
2
t AD
1
1
2
LAA  LBB 



2
 LBB  D    LAB LAB 
2

 
1
LAA
2
dynamic matrix (without spin diffusion):
 LAA
L  
 LBA
LAB 
1 T
  R  K   1A
LBB 
 0
0  1tA
  
1 T1B   1 t A
1 tB 

 1 tB 
Laser supported 1H MAS NMR
773 K
723 K
n1/2 / kHz
10
1
673 K
623 K
573 K
423 K
297 K
40
20
0 20
 / ppm
40
0.1
1.0
1.5
2.0 2.5 3.0
1000 T  / K
3.5
Spectra (at left) and Arrhenius plot
(above) of the temperature dependent
1H MAS NMR measurements which
were obtained by laser heating. The
zeolite sample H-Y was activated at
400 °C.
Laser supported high-temperature MAS NMR
for time-resolved in situ studies of reaction steps
in heterogeneous catalysis: the NMR batch reactor
B0
MAS Rotor
 7 mm
Cryo Magnet
CO2 Laser
Proton transfer between Brønsted sites and
benzene molecules in zeolites H-Y
85 H-Y with
fully deuterated
benzene at
400 K
t
10
8
4
 /ppm
0
intensity
t /min
0
200 400
In situ 1H MAS NMR spectroscopy
of the proton transfer between
bridging hydroxyl groups and
benzene molecules yields
temperature dependent exchange
rates over more than five orders of
magnitude.
600 800
F1
92 H-Y with
benzene at
520 K with a
mixing period
of 500 ms
H-D exchange and
NOESY MAS NMR
experiments were
performed by both
conventional and
laser heating up to
600 K.
2
4
6
8
F2
8
6
4
2
 /ppm
Exchange rate
as a dynamic measure of Brønsted acidity

k /min
Arrhenius plot of the H-D
and H-H exchange rates for
benzene molecules in the
zeolites 85 H-Y and 92 H-Y.
The values which are
marked by blue or red were
measured by laser heating
or conventional heating,
respectively.

10

10
10
10
92 H-Y
85 H-Y


1.5
1.9
2.3
2.7 1000
T/K
The variation of the Si/Al ratio in the zeolite H-Y causes a change of the
deprotonation energy and can explain the differences of the exchange rate of
one order of magnitude in the temperature region of 350600 K. However, our
experimental results are not sufficient to exclude that a variation of the preexponential factor caused by steric effects like the existence of non-framework
aluminum species is the origin of the different rates of the proton transfer.
I acknowledge
support from
Horst Ernst
Clemens Gottert
Johanna Kanellopoulos
Bernd Knorr
Lutz Moschkowitz
Dagmar Prager
Denis Schneider
Deutsche Forschungsgemeinschaft
Max-Buchner-Stiftung