infrared study of molecular hydrogen adsorption in metal-organic frameworks undergrad students...
Post on 19-Jan-2016
226 Views
Preview:
TRANSCRIPT
Infrared Study of Molecular Hydrogen Adsorption in Metal-Organic Frameworks
Undergrad StudentsMichael FriedmanJesse HopkinsBrian BresslauerBen ThompsonJordan Gotdank
Phys. Rev. B. 81, 104305 (2010)
Motivation: Hydrogen Storage for Fuel Cells
High Pressure
350-700 bar
Liquid Hydrogen
Metal-Organic Frameworks
Binding Energy too Weak
van der Waals Interactions
5 -10 kJ/mol
30 - 40 kJ/mol is ideal value
Act like a 3-D “Tinker Toy”
Metal ions linked by organic chains
Vast number of possible structures
Voids of ~ 10 – 20 Å
Loading Isotherm at 77 K
MOF-74
Infrared Spectroscopy to Study Adsorbed H2???
• Problem: H2 not infrared active: no dipole moment
• Matrix - H2 interactions induce dipole moments
• Spectrum is very sensitive to the intermolecular potential
• Problem: spectra are very weak
Diffuse Reflectance Spectroscopy
• Light bounces around
within powder sample
• Very long path length
enhances absorption signal
• Problem: requires large
collecting optics
Diffuse Reflectance Spectroscopy: Cryostat Assembly
Rev. Sci. Instr. 77, 093110 (2006)
Infrared Selection Rules for Adsorbed H2 (cold)
• Pure Vibrational modes called Q transitions J = 0
• Rotational Sidebands called S Transitions J = 2
• Q(0) and Q(1) should be very close in energy ~ 6 cm-1 apart
Q(0)S(0)
J = 0
J = 2
J = 1
J = 1
Para H2 Ortho H2
J = 0
J = 3
Q(1)
S(1)
Typical Spectra for H2 in MOFs at 30 KA
bso
rban
ce
48004600440042004000Frequency (cm
-1)
Q(0) and Q(1) S(0) S(1)
MOF-5
MOF-74
ZIF-8
HKUST-1
MOF-74 (M2C8H2O6) where M can be Mn, Fe, Co, Ni, and Zn
~1 nm
Neutron Diffraction Shows H2 sites
Typical Spectra for H2 in MOFs at 30 KA
bso
rban
ce
48004600440042004000Frequency (cm
-1)
Q(0) and Q(1) S(0) S(1)
MOF-5
MOF-74
ZIF-8
HKUST-1
Typical Spectra for H2 in MOFs at 30 KA
bso
rban
ce
48004600440042004000Frequency (cm
-1)
Q(0) and Q(1) S(0) S(1)
MOF-5
MOF-74
ZIF-8
HKUST-1
Pure Vibrational Q-region of H2 : Zn_MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Pure Vibrational Q-region of H2 in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Pure Vibrational Q-region of H2 in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Pure Vibrational Q-region of H2 in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2Liu et al. Langmuir 24, 4772 (2008)
Pure Vibrational Q-region of H2 in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Pure Vibrational Q-region of H2 in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Pure Vibrational Q-region of H2 in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
1 Q(1) gas phase
Q(0) gas phase
2
T
Pure Vibrational Q-region of H2 in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
1 Q(1) gas phase
Q(0) gas phase
2
T
MOF-74 Hydrogen Sites (Neutron Diffraction)
Primary Sites Separated by ~ 5 Å
Primary Sites Separated by ~ 5 Å
Primary-Secondary Separation ~ 2.9 Å
MOF-74 Hydrogen Sites (Neutron Diffraction)
Pure Vibrational Q-region of H2 in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
1 Q(1) gas phase
Q(0) gas phase
2
T
Para Enhanced H2 (J =0) in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
1 Q(1) gas phase
Q(0) gas phase
2
T
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
1 Q(1) gas phase
Q(0) gas phase
2
T
Para Enhanced H2 (J =0) in MOF-74 at 30 KA
bso
rban
ce (
a.u
.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
Q(1) gas phase
Q(0) gas phase
2
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
1 Q(1) gas phase
Q(0) gas phase
2
T
Ab
sorb
ance
(a.
u.)
4200416041204080
Frequency (cm-1)
1 Q(1) gas phase
Q(0) gas phase
2
T
Ortho to Para Conversion with TimeA
bso
rban
ce (
a.u
.)
412041104100409040804070
Frequency (cm-1)
5 minutes 15 minutes 25 minutes 35 minutes 100 minutes
Q(1)
Q(0)
MOF-74 Metal Ion Comparison
Ab
sorb
ance
42004150410040504000Frequency (cm
-1)
Zn
Mn
Co
Ni
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Primary Site - Metal Separated by 2.6 Å
Secondary Site – Metal Separated by 4.3 Å
MOF-74 Metal Hydrogen Distance
Ab
sorb
ance
42004150410040504000Frequency (cm
-1)
Zn
Mn
Co
Ni
Irving-Williams SeriesSc Ti V Cr Mn Fe Co Ni Cu Zn
Irving-Williams Ligand Stability Mn < Fe < Co < Ni > Zn
Vibrational Red-Shift vs Binding Energy
12
10
8
6
4
2
0
Bin
ding
Ene
rgy
(kJ/
mol
)
120100806040200
Redshift (cm-1)
Mn-MOF-74Co-MOF-74
Ni-MOF-74
Zn-MOF-74
HKUST-1
MOF-5
ZIF-8
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
160K
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
140K
160K
1
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
120K
140K
160K
1
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
100K
120K
140K
160K
1
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
90K
100K
120K
140K
160K
1
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
80K
90K
100K
120K
140K
160K
1
2
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
70K
80K
90K
100K
120K
140K
160K
12
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
60K
70K
80K
90K
100K
120K
140K
160K
12
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
50K
60K
70K
80K
90K
100K
120K
140K
160K
12
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
40K
50K
60K
70K
80K
90K
100K
120K
140K
160K
1 2
3
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
30K
40K
50K
60K
70K
80K
90K
100K
120K
140K
160K
1 23
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
30K
40K
50K
60K
70K
80K
90K
100K
120K
140K
160K
20K
1 2 3
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
416041404120410040804060404040204000
Frequency (cm-1
)
30K
40K
50K
60K
70K
80K
90K
100K
120K
140K
160K
20K
15K
1 2 3
Temperature Dependent Spectra Co-MOF-74
Overtones of H2 in MOF-74
0.6
0.4
0.2
0.0
Ab
sorb
ance
80007000600050004000Frequency (cm
-1)
Overtones of H2 in MOF-74
Ab
sorb
ance
-250 -200 -150 -100 -50 0Frequency (cm
-1)
Ab
sorb
ance
-120 -100 -80 -60 -40 -20 0Frequency (cm
-1)
Fundamental Red Shift Overtone Red Shift
Intense overtone peak only present for exposed metal site
Conclusion
• Diffuse Reflectance Infrared Spectroscopy ideal for probing adsorbed H2
• Concentration dependent spectra provide information about the nature of the binding site
• In MOF-74 vibrational red-shift follows Irving Williams sequence Zn < Mn < Co < Ni
• Intense overtone peak for H2 in exposed metal site
• Data analysis qualitatively ok. Need real modeling
top related