Motivation: CO 2 capture System: Metal-Organic Frameworks Data:
Unusual blue shift of adsorbed CO 2 3 mode Room-temperature
sidebands Low-temperature bands reveal 2 nd configuration
Vibrational Shift of Adsorbed CO 2 within a Metal-Organic Framework
Outline
Slide 2
Motivation Carbon capture Separate carbon dioxide from exhaust
gases Emissions reduction accompanying switch to clean energy
sources Natural gas purification Separate CO 2 from methane (CH 4 )
Improve energy density of fuel, decrease pipe corrosion Current CO
2 separation methods are costly Harmful materials High energy costs
for regeneration A better way?
http://www.nma.org/ccs/carboncapture.as p
Slide 3
Metal-Organic Frameworks Large voids, voids of ~ 10 20 for
molecular storage and separation Complex unit cell makes
computation modeling challenging Significant van der Waals
interactions Metal ions linked by organic chains Very low density
Crystalline and tunable Vast number of possible structures
Slide 4
Honeycomb structure Metal-oxide clusters linked by Benzene
rings MOF-74 H. Wu et al. J. Phys. Chem. Lett., 1(13):19461951,
2010. Diffraction indicates CO 2 is nearly linear 2+ Unsaturated
metal ion acts as primary binding site for CO 2 2.4
Slide 5
MOF-74 Isostructural Series
http://legacy.owensboro.kctcs.edu/gcaplan/bio/Notes/BIO%20Notes%20C%20intro%20chem.htm
Same structure, different metal Mg-MOF-74, Mn-MOF-74,
Fe-MOF-74,Co-MOF-74, Zn-MOF-74
Slide 6
Slide 7
MOF-74 Selective Binding Binding energy in Mg-MOF-74 ~ 40 - 50
kJ/mol Binding energy in other MOF-74 at least 7 kJ/mol less
Difference is likely due to direct electrostatic interaction via
shorter Mg O bond Binding energy for CH 4 in MOF-74 ~ 20 kJ/mol
Difference between CO 2 and CH 4 mainly attributed to CO 2
quadrupole moment Caskey et al. J. Am. Chem. Soc., 130,10870,
(2008). H. Wu et al. J. Am. Chem. Soc., 131, 4995 (2009). Park et
al. Phys. Chem. Lett. 3, 826 (2012). Yao et al. Phys. Rev. B. 85,
64302 (2012).
Slide 8
Diffuse Reflectance Spectroscopy Light bounces around within
powder sample Very long path length enhances absorption signal
Side Bands: Translational/Librational 000 001 010 011 C 13
Slide 14
Librational Motion
Slide 15
MOF-74 H. Wu et al. J. Phys. Chem. Lett., 1(13):19461951, 2010.
2+
Slide 16
Temperature Dependence E B = 0.7 0.1 kJ/mol New band emerges
below 150 K Degeneracy ratio of ~ 2 Room temperature peaks too
broad to resolve
Slide 17
vdW-DF2 Theory Calculations Y. Yao et al. Phys. Rev. B, 85,
064302 ( 2012). Predicts sites 2.96 and 3.09 away from metal with
0.8 kJ/mol energy difference
Slide 18
Combination modes compared to Hitran Data 3 000 001 3 + Fermi
resonance 000 101 and 000 021 3 + 2 x Fermi resonance 000 201, 041,
121
Slide 19
Conclusion CO 2 in MOF-74 Mg version 3 mode unique in showing
blue shift All other modes show red shift Evidence for CO 2
librational/translational motion Evidence for a 2 nd nearly
degenerate adsorbed CO 2 configuration
Slide 20
Michael Friedman Jordan Gotdank Jesse Hopkins Brian Burkholder
Ben Thompson Chris Pierce Jennifer Schloss Undergrad Students