infrared spectroscopy of h2 in mofs - oberlin
TRANSCRIPT
Infrared Spectroscopy of H2 in MOFs 1) More than just a characterization technique
2) Experimental probe of H2∙∙∙MOF interactions
3) Requires some specialized equipment
4) Storage, quantum sieving, catalysis
5) CO2, CH4, N2, other gases
Infrared Spectroscopy! Are you crazy?
H H
Infrared Spectroscopy! Are you crazy?
The atoms are neutral
No Dipole moment
H H
Infrared Spectroscopy! Are you crazy?
Interactions with MOF can polarize H2
H H
H H
The atoms are neutral
No Dipole moment
Infrared Spectroscopy! Are you crazy?
H H
H H Interactions with MOF can polarize H2
The atoms are neutral
No Dipole moment
Infrared Spectroscopy! Are you crazy?
H H
H H Interactions with MOF can polarize H2
The atoms are neutral
No Dipole moment
H2 polarizability is almost isotropic Mostly activates pure vibrational transitions
H2 Quadrupole Mechanism
Hydrogen polarizes MOF atoms
Quadrupole moment highly anisotropic Vibrations and Ro-vibrations are activated
H2 quadrupole moment can polarize MOF atoms
Diffuse Reflectance Infrared Spectroscopy
1) Long effective optical path length
2) Powder sample require no processing
3) Typically use 10 mg of powder
4) Sample chamber can be quite small
Diffuse Reflectance Spectroscopy: Cryostat Assembly
Rev. Sci. Instr. 77, 093110 (2006)
Samples are mounted in a glove-box
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Quantum Dynamics of Adsorbed H2
• Vibration
• Rotation
• Translation Center-of-mass On the order of 100 cm-1
= 4161 cm-1 for free H2
= 59 cm-1 for free H2
( ) 02/1 vvEv +=
( ) 01 BJJEJ +=
0ν
0B
Spectroscopic notation of possible transitions
• Pure Vibrational modes called Q transitions ∆J = 0
• Q(0) and Q(1) are very close in
energy ~ 6 cm-1 apart
• Rotational Sidebands called S Transitions ∆J = 2
Q(0) 4161
S(0) 4498
ν=1 J = 0
J = 2
J = 1
J = 1
Para H2 Ortho H2 ν =0 J = 0
J = 3
Q(1) 4155
S(1) 4713
Typical Spectra for H2 in MOFs at 30 K A
bsor
banc
e
48004600440042004000Frequency (cm-1)
Q(0) and Q(1) S(0) S(1)
MOF-5
MOF-74
ZIF-8
HKUST-1
Vibrational Redshift as a Function of Binding Energy
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)
140K160K
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)
120K140K160K
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)
100K120K140K160K
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)
90K100K120K140K160K
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)
80K90K
100K120K140K160K
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)
70K80K90K
100K120K140K160K
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)
60K70K80K90K
100K120K140K160K
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)
50K60K70K80K90K
100K120K140K160K
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)
40K50K60K70K80K90K
100K120K140K160K
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)
30K40K50K60K70K80K90K
100K120K140K160K
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)
30K40K50K60K70K80K90K
100K120K140K160K
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)
30K40K50K60K70K80K90K
100K120K140K160K
20K15K
1 2 3
Temperature Dependent Spectra Co-MOF-74
Spectra as a function of concentration (Mg-MOF-74 at 35 K)
VL VS
J. Am. Chem. Soc. 2011,133, 20310
Quantum Dynamics of Adsorbed H2
• Vibration
• Rotation
• Translation Center-of-mass On the order of 150 cm-1
= 4161 cm-1 for free H2
= 59 cm-1 for free H2
( ) 02/1 vvEv +=
( ) 01 BJJEJ +=
0ν
0B
Translational mode energy (quantum sieving?)
Back of the Envelope Calculation
Eb
E=0
H2 D2
Standard Separation Techniques
Rae, H. K. Selecting Heavy Water Processes; ACS Symposium Series 68, American Chemical Society: Washington, DC1978.
Selectivity vs Translational Frequency
Dashed line shows simple back of the envelope Solid line shows full (harmonic) thermodynamic calculation
J. Am. Chem. Soc. 2013, 135, 9458−9464
H2 and D2 Mixtures in Mg-MOF-74
H2 and D2 Mixtures (After sitting at room temperature)
Mass Spectroscopy HD formation at room temperature
Mass Spectroscopy HD formation at room temperature
Pristine Air-Exposed
Mass Spectroscopy HD formation at room temperature
Pristine Air-Exposed Reactivated 180 oC
H2 and D2 Mixtures (After sitting at room temperature)
Fundamental
Overtone
Deuterium in MOF-5
Pure MOF-5 MOF-5 with D2
Inte
nsity
In
tens
ity
Frequency Shift Fundamental versus Overtone
Secondary
D2
H2
HD
D2
HD
H2
Q(1) Q(0) Fundamental
Overtone
J. Mol. Spect. 2015, 307, 20-26
Direct Experimental Evidence of Binding Mechanism?
J. Am. Chem. Soc. 136, 17827 (2014) Tsivion, Long, and Head-Gordon
How could we most directly determine the relative contribution of these three mechanisms? “More direct” implies less need for theoretical modelling.
Typical Spectra for H2 in MOFs at 30 K A
bsor
banc
e
48004600440042004000Frequency (cm-1)
Q(0) and Q(1) S(0) S(1)
MOF-5
MOF-74
ZIF-8
HKUST-1
Binding Sites in MOF-5
J.L.C. Rowsell, E.C. Spencer, J. Eckert, J. Howard, and O.M. Yaghi, Science, 309, 1350 (2005)
E. Spencer, J. Howard, G. McIntyre, J. L. C. Rowsell, and O. M. Yaghi, Chem. Commun. 3, 278 (2006).
MOF-5 Temperature Dependence
Concentration Dependence
MOF-5 with H2 Molecules at Primary Site
Stick Spectrum for Interacting ortho-H2 Pairs
Ortho to Para Conversion with Time
H2 and D2 Mixture
CO2 in Different Metal MOF-74 J. Phys. Chem. C 2015, 119, 5293-5300
Acknowledgements
Jesse Rowsell 1977-2015
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