No Slide Titleweb.mit.edu/sequestration/talloires/2_to_page_pdfs/Talloires_Snurr.pdfR.Q. Snurr, M. O’Keeffe, J. Kim, O.M. Yaghi, “Ultra-high porosity in metal-organic frameworks,”

Molecular Modeling and Design of Metal-Organic Frameworks

for CO2 Capture

Randy Snurr

Department of Chemical & Biological Engineering Northwestern University, Evanston, IL 60208

http://zeolites.cqe.northwestern.edu

Adsorption Separations

PSA, TSA, VSA

Adsorption separations• are widely used in processes such as

air separation• can be more energy efficient than

traditional distillation separations• can be based on differences in

adsorption thermodynamics (more common) or rates of diffusion (less common)

A key issue is the choice of the adsorbent

Novel adsorbent

“Nanotechnology for Carbon Dioxide Capture,” R.R. Willis, A.I. Benin, R.Q. Snurr, A.O. Yazaydin, in Nanotechnology for the Energy Challenge, J. Garcia-Martinez, Ed., Wiley-VCH, 2010.

Use specific transition-metal coordination chemistry:

Metal corners and organic linkers can be chosen to yield a wide variety of porous, crystalline structures� Pores or cavities of controlled sizes� Wide variety of chemical functionalities

A Building-block Approach to Materials Synthesis

+

Metal-Organic Frameworks

3D frameworks

• crystalline

• very open structures

• potential applications in energy storage, sensing,adsorption separations, and catalysis

Snurr, Hupp, Nguyen, 2004

Potential foradsorptionapplications

Example: IRMOFs IsoReticular Metal-Organic Frameworks

=

Zn4O

=

O O

OO

O O

OO

O

O

O O

OO

IRMOF-1 IRMOF-4 IRMOF-10

Omar Yaghi, Univ. California, Los Angeles

IRMOFs

Pyridine-only frameworks are generally unstable against channel collapse. However, a family of mixed-ligand MOFs shows permanent microporosity.

(1) Carboxylate paddle-wheel-type

coordination of Zn(II) pairs

2D sheets

(2) Pyridine/Zn linkages

open frameworks

[Ma, Mulfort, Hupp, Inorg. Chem. 2005

Mixed-Ligand MOFs

MOF-177

Diversity of MOFs

MOF-177

HKUST-1MIL-103

MIL-53

Molecular Tinker Toys

H. Furukawa, N. Ko, Y.B. Go, N. Aratani, S.B. Choi, E. Choi, A.Ö. Yazaydin, R.Q. Snurr, M. O’Keeffe, J. Kim, O.M. Yaghi, “Ultra-high porosity in metal-organic frameworks,” Science, in press.

Ultra-High Surface Area

• Extended linker lengths

• MOF-210 has the largest specific surface area reported to date: 6240 m2/g BET.

• These large-pore MOFs have very high capacity for CO2 at higher pressures.

Materials Design

?

Can tune material properties via synthesis• pore size• linker functionality• open-metal sites• extraframework cations or anions

Can also modify MOFs after their synthesis

• Screening of MOFs for CO2 Capture with Molecular Modeling– Model development– Test of model versus experiment– Screening results

• Identify candidate MOFs• What do we learn?

• Post-Synthesis Modification of MOFs for Improved CO2 Uptake

• Summary and Outlook

Outline

Simulation Model

• MOF atoms are held fixed at their crystallographic coordinates.

• Lennard-Jones parameters taken from the DREIDING force field.

• Charges on framework atoms from quantum chemical calculations.

� Atomistic representation of MOFs

� Atomistic representation of guest CO2 molecules• CO2/CO2 parameters taken from

TraPPE force field that matches bulk vapor/liquid equilibria*

• Lennard-Jones + Coulomb-0.35 -0.35+0.7

1.16 Å

* Potoff, Siepmann, AIChE J., 2001.

A phase equilibrium problem

At equilibrium:

TI = TII

PI = PII

µIi = µII

i for all species i

(or fiI = fiII for all species i)

Molecular Simulation of Adsorption

MOF phase, II

Fluid phase, I

Grand Canonical Monte Carlo (GCMC)

� adsorbed phase in equilibrium with bulk fluid

� µ, V, T constant as in adsorption experiments

� number of molecules fluctuates

� random moves

insertions

deletions of molecules

µ T

HKUST-1 ZIF-8

Yazaydin, Snurr, Park, Koh, Liu, LeVan, Benin, Jakubczak, Lanuza, Galloway, Low, Willis, J. Am. Chem. Soc., 2009.

CO2 Adsorption in MOFs

298 K IRMOF-1

Walton, Millward, Dubbeldam, Frost, Low, Yaghi, Snurr, J. Am. Chem. Soc., 2008.


0 20 40 60 80 100 1200

200

400

600

800

1000

1200

1400

1600

1800

2000

CO

2 Loa

ding

, mg/

g

Pressure, kPa

195K 233K 208K 273K 218K GCMC

0 800 1600 2400 32000

200

400

600

800

1000

1200

1400

1600

CO

2 Loa

ding

, mg/

g

Pressure, kPa

MOF-177 IRMOF-3 GCMC

Systematic Comparison with Experiment

Farrusseng, Daniel, Gaudillere, Ravon, Schuurman, Mirodatos, Dubbeldam, Frost, Snurr, Langmuir, 2009.

N2 CH4

Kr CO2

Xe

0 -5 -10 -15 -20 -25 -300

-5

-10

-15

-20

-25

-30

�H s

imul

atio

n / K

J.m

ol-1

�H experimental / KJ.mol-10 -5 -10 -15 -20 -25 -30

0

-5

-10

-15

-20

-25

-30

�H s

imul

atio

n / K

J.m

ol-1

�H experimental / KJ.mol-1

N2

CH4

KrCO2

Xe

n-C4H10

i-C4H10

IRMOF-1 IRMOF-3

Screening MOFs for CO2 Capture

� Given the large number of possible MOF topologies, linkers, and metal nodes, there are an almost unlimited number of MOFs that could be synthesized.

� Screening and understanding of the fundamental structure/function relationships are, thus, very important for developing new processes based on MOFs.

� Choose a diversity of materials for screening to help improve our understanding of CO2 capture in MOFs.

CO2/MOF Screening Collaboration

� Team Approach– Synthesis– Characterization– Testing– Modeling

� Team Members– Richard Willis, Annabelle Benin, Syed Faheem, John Low at

UOP LLC, Des Plaines, IL– Adam Matzger at University of Michigan, Ann Arbor– Douglas LeVan at Vanderbilt University– Stefano Brandani at University of Edinburgh– Ozgur Yazaydin at Northwestern University


14 MOFs

� Mg\DOBDC� Ni\DOBDC� Co\DOBDC� Zn\DOBDC� Pd(2-pymo)2

� HKUST-1� UMCM-150(N)2

� UMCM-150� MIL-47� ZIF-8� IRMOF-1� IRMOF-3� UMCM-1� MOF-177

M\DOBDC (1D Channels)

Pd(2-pymo)2

(Narrow pores)

UMCM-1(High surface area)

HKUST-1(Side pockets)

Experimental CO2 uptake at 0.1 bar and 298 K

M\DOBDC MOFs perform particularly well.� MOFs with large free volume

perform the worst at low pressure.

� MOFs having coordinatively unsaturated metal sites (open-metal sites) demonstrate the best performance.




Yazaydin et al., J. Am. Chem. Soc., 2009.

No correlation with SA

No correlation with free volume

There is a strong correlation between CO2 uptake and heat of adsorption at low pressure.


CO2 density profile in Mg\DOBDC at 0.1 bar from simulations.

Location of adsorbed CO2 molecules in Ni\DOBDC from X-ray diffraction data and IR spectroscopy.

Dietzel, Johnsen, Fjellvag, Bordiga, Groppo, Chavan, Blom, Chem. Comm. 2008.

Why do M\DOBDCs perform better than other MOFs which also have open-metal sites?


Why do M\DOBDCs perform better than other MOFs which also have open-metal sites?

MOF Sites / nm2 Sites / nm3

Mg\DOBDC 3.031 7.074

Ni\DOBDC 2.655 7.298

Co\DOBDC 2.559 7.109

Zn\DOBDC 2.798 7.564

HKUST-1 1.400 3.730

UMCM-150 0.738 2.015

UMCM-150(N)2 0.764 2.036

Surface and free volume density of metal atoms in MOFs with open-metal sites

Simulation versus Experiment

Experiment GCMC

Mg-MOF-74 1 2

Ni-MOF-74 2 3

Co-MOF-74 3 5

Zn-MOF-74 4 4

Pd(2-pymo)2 5 1

HKUST-1 6 6

UMCM-150(N2) 7 9

UMCM-150 8 8

MIL-47 9 7

ZIF-8 10 11

IRMOF-3 11 10

UMCM-1 12 12

MOF-177 13 13

IRMOF-1 14 14

This diverse set of MOFs is a stringent test of simulation.

• Ranking from simulation is very close to that from experiment.

• The top 5 MOFs are correctly identified by the simulations.

Simulation versus Experiment

Simulation vs. experiments at room temperature

� There is generally good agreement between predicted and measured adsorption, R2 = 0.67.

� One exception is the M\DOBDC samples, particularly at 0.1 bar (open blue circles). If the M\DOBDC data at 0.1 bar are excluded, R2 = 0.79.

� The simulations perform well, with a level of agreement that is satisfactory for screening purposes.

Yazaydin et al., J. Am. Chem. Soc., 2009.

Limitations of the Model

Model underpredicts adsorption on the open-metal sites.

Since classical model does not include orbital interactions, this is expected.

• Screening of MOFs for CO2 Capture with Molecular Modeling– Model development– Test of model versus experiment– Screening results

• Identify candidate MOFs• What do we learn?

• Post-Synthesis Modification of MOFs for Improved CO2 Uptake

• Summary and Outlook

Outline

Post-Synthesis Modification of MOFs

Hypothesis• Fluorine groups

will increase CO2uptake

• Change in pore size may also play a role in CO2selectivity over N2

1 3

4

+

Zn(NO3)·H2O

5

100oC

150oC

1) Soak in CHCl3/4-(trifluoromethyl)pyridine

2) Heating at 100 C

Pyridine-CF3

Dimethylformamide

(DMF)

Bae, Farha, Hupp, Snurr, J. Mater. Chem., 2009.

Enhancement of CO2 / N2 Selectivity

Pressure [bar]

0 2 4 6 8

Se

lec

tivit

y [

-]

0

10

20

30

40

50

3 (with coordinated solvents)

4 (with open metal sites)

5 (with Py-CF3 ligands)

CO2 / N2 SelectivityCavity modification can be used to enhanceselectivity.

These are among the highestselectivities reported.

Need to increase the capacities.

Selectivity

Selectivities predicted from ideal adsorbed solution theory

BB

AA

y/x

y/x��

Bae, Farha, Hupp, Snurr, J. Mater. Chem., 2009.

HKUST-1 (Cu-BTC)*

� Cubic unit cell

� 0.5/0.9 nm pores

� Cu2 corners

� Benzene-1,3,5-tricarboxylate linker

� As synthesized HKUST-1 has one coordinated water molecule per Cu

� HKUST-1 has been the subject of numerous experimental and modeling studies.

*Chui, Lo, Charmant, Orpen, Williams, Science, 1999.

Effect of Coordinated Water Molecules

CO2 Simulations CO2 Experiments

Yazaydin, Benin, Faheem, Jakubczak, Low, Willis, Snurr, Chem. Mater., 2009.


298 K

HKUST-1 ZIF-8



Selectivity for CO2 over N2 from mixture GCMC simulations

� Significant increase in selectivity if water molecules are present.

� Axial ligation of coordinatively unsaturated metal sites by various molecules could open up new possibilities for tuning the adsorption behavior of MOFs for CO2 capture and other applications.


Yazaydin, Benin, Faheem, Jakubczak, Low, Willis, Snurr, Chem. Mater., 2009.

SelectivityBB

AA

y/x

y/x��

� We have screened a diverse set of 14 metal-organic frameworks for low-pressure CO2 uptake using a consistent, predictive molecular modeling approach.

� The model was validated against experiments. Given this validation, the molecular model can aid in selection of MOFs for flue gas separation by screening a large number of materials and providing insight into the mechanism of CO2 adsorption.

� Parameters from generalized force fields are usually good enough to predict experimental data. However, the model can be further improved to account for the strong interactions between open-metal sites and CO2.

� MOFs with a high density of open-metal sites are good candidates for CO2 capture from flue gas.

Summary

• Strengths of MOFs– Huge variety of potential structures– Ready functionalization– Heats of adsorption are lower than zeolites– Molecular modeling can be used for screening

• Challenges for MOFs– MOFs with high CO2 uptake tend to adsorb water– Stability in flue gas environment– Cost uncertainties

Outlook

Acknowledgments

• Post-docs– A. Özgür Yazaydin – Krista Walton (Georgia Tech)– David Dubbeldam (U. Amsterdam)

• Screening Collaborators– Rich Willis (UOP) – John Low (UOP)– Annabelle Benin (UOP) – M. Doug LeVan (Vanderbilt U.)– Stefano Bandani (U. Edinburgh) – Adam Matzger (U. Michigan)

• Other Collaborators– Omar Yaghi (UCLA) – David Farrusseng (CNRS)

• Northwestern Collaborators– Joseph Hupp – SonBinh Nguyen

• Funding– Department of Energy, NETL– Department of Energy, Basic Energy Sciences– TeraGrid Computing Resources

298 K

Walton, Millward, Dubbeldam, Frost, Low, Yaghi, Snurr, J. Am. Chem. Soc., 2008.


0.1 1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

CO

2 Den

sity

, g/c

m3

Pressure, bar

IRMOF-1 IRMOF-10 IRMOF-16�b, 298K

Documents

No Slide Titleweb.mit.edu/sequestration/talloires/2_to_page_pdfs/Talloires_Snurr.pdfR.Q. Snurr, M. O’Keeffe, J. Kim, O.M. Yaghi, “Ultra-high porosity in metal-organic frameworks,”