Infrared Spectroscopy of H2 in MOFs - Oberlin

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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