Infrared Spectroscopy of H 2 in MOFs

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1 Infrared Spectroscopy of H 2 in MOFs 1) More than just a characterization technique 2) Experimental probe of H 2 MOF interactions 3) Requires some specialized equipment 4) Storage, quantum sieving, catalysis 5) CO 2, CH 4, N 2, other gases

2 Infrared Spectroscopy! Are you crazy? H H

3 Infrared Spectroscopy! Are you crazy? H H The atoms are neutral No Dipole moment

4 Infrared Spectroscopy! Are you crazy? H H The atoms are neutral No Dipole moment H H Interactions with MOF can polarize H 2

5 Infrared Spectroscopy! Are you crazy? H H The atoms are neutral No Dipole moment H H Interactions with MOF can polarize H 2

6 Infrared Spectroscopy! Are you crazy? H H The atoms are neutral No Dipole moment H H Interactions with MOF can polarize H 2 H 2 polarizability is almost isotropic Mostly activates pure vibrational transitions

7 H 2 Quadrupole Mechanism H 2 quadrupole moment can polarize MOF atoms Quadrupole moment highly anisotropic Vibrations and Ro-vibrations are activated Hydrogen polarizes MOF atoms

8 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

9 Diffuse Reflectance Spectroscopy: Cryostat Assembly Rev. Sci. Instr. 77, (2006)

10 Samples are mounted in a glove-box

11 This image cannot currently be displayed.

12 Quantum Dynamics of Adsorbed H 2 Vibration E v = v + 1/ 2 v ν 0 ( ) 0 = 4161 cm -1 for free H 2 Rotation E J = J ( J + 1) B 0 B 0 = 59 cm -1 for free H 2 Translation Center-of-mass On the order of 100 cm -1

13 Spectroscopic notation of possible transitions J = 3 Pure Vibrational modes called Q transitions J = 0 J = 2 ν=1 J = 0 J = 1 Q(0) and Q(1) are very close in energy ~ 6 cm -1 apart Rotational Sidebands called S Transitions J = 2 ν =0 J = 0 Q(0) 4161 S(0) 4498 J = 1 Q(1) 4155 S(1) 4713 Para H 2 Ortho H 2

14 Typical Spectra for H 2 in MOFs at 30 K Q(0) and Q(1) S(0) S(1) MOF-74 Absorbance HKUST-1 ZIF-8 MOF Frequency (cm -1 )

15 Vibrational Redshift as a Function of Binding Energy

16 Temperature Dependent Spectra Co-MOF K 20K 30K 40K 50K 60K 70K 80K 90K 100K 120K 140K 160K Frequency (cm -1 )

17 Spectra as a function of concentration (Mg-MOF-74 at 35 K) J. Am. Chem. Soc. 2011,133, V L VS

18 Quantum Dynamics of Adsorbed H 2 Vibration E v = v + 1/ 2 v ν 0 ( ) 0 = 4161 cm -1 for free H 2 Rotation E J = J ( J + 1) B 0 B 0 = 59 cm -1 for free H 2 Translation Center-of-mass On the order of 150 cm -1

19 Translational mode energy (quantum sieving?)

20 Back of the Envelope Calculation E=0 E b H 2 D 2

21 Standard Separation Techniques Rae, H. K. Selecting Heavy Water Processes; ACS Symposium Series 68, American Chemical Society: Washington, DC1978.

22 Selectivity vs Translational Frequency J. Am. Chem. Soc. 2013, 135, Dashed line shows simple back of the envelope Solid line shows full (harmonic) thermodynamic calculation

23 H 2 and D 2 Mixtures in Mg-MOF-74

24 H 2 and D 2 Mixtures (After sitting at room temperature)

25 Mass Spectroscopy HD formation at room temperature

26 Mass Spectroscopy HD formation at room temperature Pristine Air-Exposed

27 Mass Spectroscopy HD formation at room temperature Pristine Air-Exposed Reactivated 180 o C

28 H 2 and D 2 Mixtures (After sitting at room temperature)

29 Deuterium in MOF-5 Pure MOF-5 MOF-5 with D 2 Intensity Fundamental Intensity Overtone

30 Frequency Shift Fundamental versus Overtone J. Mol. Spect. 2015, 307, Q(1) Q(0) Secondary D 2 HD H 2 D 2 HD Fundamental Overtone H 2

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32 Direct Experimental Evidence of Binding Mechanism? How could we most directly determine the relative contribution of these three mechanisms? J. Am. Chem. Soc. 136, (2014) Tsivion, Long, and Head-Gordon More direct implies less need for theoretical modelling.

33 Typical Spectra for H 2 in MOFs at 30 K Q(0) and Q(1) S(0) S(1) MOF-74 Absorbance HKUST-1 ZIF-8 MOF Frequency (cm -1 )

34 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).

35 MOF-5 Temperature Dependence

36 Concentration Dependence

37 MOF-5 with H 2 Molecules at Primary Site

38 Stick Spectrum for Interacting ortho-h 2 Pairs

39 Ortho to Para Conversion with Time

40 H 2 and D 2 Mixture

41 CO 2 in Different Metal MOF-74 J. Phys. Chem. C 2015, 119,

42 Acknowledgements Jesse Rowsell

43 Undergraduate Students on Our Papers Kelty Allen Ross Myers Jenny Schloss Jesse Hopkins Patrick Landreman John Matters Brian Burkholder Michael Friedman Ben Thompson Chris Pierce Elizabeth Gilmour Jocienne Nelson