Unconventional and Highly Selective CO Adsorption in ... · using the Micromeritics software. Adsorption isotherms at 25 °C, 35 °C, and 45 °C were measured using a recirculating

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Supporting Information for:

Unconventional and Highly Selective CO2 Adsorption in Zeolite SSZ-13

Matthew R. Hudson,1,2

Wendy L. Queen,1 Jarad A. Mason,

3 Dustin W. Fickel,

4 Raul F.

Lobo,4* and Craig M. Brown

1,5*

1National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, MD 20899-6102, USA

2Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742-2115, USA

3Department of Chemistry, University of California, Berkeley, CA 94720, USA 4Center for Catalytic Science and Technology, Department of Chemical Engineering, University

of Delaware, Newark, DE 19716, USA 5The Bragg Institute, Australian Nuclear Science and Technology Organisation, PMB1 Menai,

NSW, Australia

*Corresponding author e-mail: [email protected], [email protected]

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Contents

S1. Zeolite synthesis and cation exchange experimental

S2. Adsorption isotherms, isosteric heat of adsorption and IAST selectivity calculations

S3. Powder neutron diffraction details

S4. Modeling of the CO2 and N2 interaction with the 8-ring window

S5. References

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S1. Zeolite Preparation and Cation Exchange

Structure-Directing Agent Synthesis.

The structure-directing agent (SDA) used in the synthesis of SSZ-13 was N,N,N-trimethyl-

1-adamantanamine iodide (TMAAI).1 TMAAI was synthesized by adding 10 g of 1-

adamantanamine (97%, Sigma-Aldrich*) to 24.8 g of methanol (Fisher Scientific) and stirring

until the solid is dissolved. Next, 29 g of tributylamine (98.5%, Sigma-Aldrich) was added to the

solution and stirred for 15 min. The solution was then placed in an ice bath, and 28.4 g of methyl

iodide (99.5% Sigma-Aldrich) was added dropwise into the solution. This solution was stirred

for 5 days at RT. After the addition of 100 mL of diethyl ether (Fisher Scientific) to precipitate

the product, the solution was further stirred for 30 min. The product was then vacuum-filtered

with more diethyl ether and dried at room temperature overnight.

Zeolite Synthesis.

SSZ-13 was synthesized using a procedure similar to that reported by Zones.2 First, 5 g of

sodium silicate (Sigma Aldrich) and 0.16 g of NaOH (Fisher Scientific) were added to 12 g of

water. The resulting solution was stirred at room temperature for 15 min; then, 0.5 g of NH4-Y

(Zeolyst CBV100) was added to the solution and stirred for 30 min. Next, 0.8 g of N,N,N-

trimethyl-1-adamantanamine iodide was added to the solution and stirred for another 30 min.

The resulting solution was then transferred into Teflon-lined auto- claves and heated at a

temperature of 140 °C under rotation for 6 days. The product was recovered by vacuum

filtration, washed with deionized water, and dried at room temperature. The as-made product was

* Certain commercial suppliers are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by NIST nor does it imply that the materials, equipment, or software identified are necessarily the best available for the purpose.

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then calcined in air at 550 °C for 8 h. and heated at a temperature of 150 °C under rotation for 6

days. The product was recovered by vacuum filtration, washed with deionized water, and dried at

room temperature. After calcination, all zeolite samples were ion-exchanged in a 0.1 M solution

of NH3NO3 (Fisher Scientific) at 80 °C for 8 h and dried in air at room temperature.

Copper Ion Exchange.

A 0.5 L solution of 0.1 M Cu(II)SO4 was made by adding 7.98 g of copper(II) sulfate

(Sigma-Aldrich) to 0.5 L of water. The pH of the solution was then adjusted to 3.5 by the

addition of nitric acid (Fisher Scientific). NH4-SSZ-13 (0.91 g) was then added to the CuSO4

solution. This solution was stirred in an oil bath at 80 °C for 1 h. Solutions were then vacuum-

filtered with deionized water, and the resulting Cu-zeolite products were dried at room

temperature.

Initial Characterization.

Powder X-ray diffraction (XRD) data were collected on a Philips X’pert diffractometer

using a Cu KR source. The patterns were obtained from 5 to 50�2θ using a step size of 0.02�2θ

and 2 s per step. Scanning electron microscopy (SEM) images and energy-dispersive X-ray spec-

troscopy (EDAX) chemical analysis were obtained on a JEOL JSM7400F microscope.

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S2. Adsorption Experimental Details.

Low-Pressure Gas Sorption Measurements.

UHP-grade (99.999% purity) carbon dioxide, nitrogen, and helium were used for all

adsorption measurements. Gas adsorption isotherms for pressures in the range 0-1.1 bar were

measured using a Micromeritics ASAP 2020 instrument.* Samples of H-SSZ-13 and Cu-SSZ-13

were transferred to preweighed analysis tubes, which were capped with a Transeal. The samples

were evacuated on the ASAP until the outgas rate was less than 2 mTorr/min. The evacuated

analysis tubes containing degassed samples were then carefully transferred to an electronic

balance and weighed to determine the mass of sample (134 mg for H-SSZ-13 and 130 mg for

Cu-SSZ-13). The tube was transferred back to the analysis port of the gas adsorption instrument.

The outgas rate was again confirmed to be less than 2 mTorr/min. Langmuir surface areas were

determined by measuring N2 adsorption isotherms in a 77 K liquid nitrogen bath and calculated

using the Micromeritics software. Adsorption isotherms at 25 °C, 35 °C, and 45 °C were

measured using a recirculating dewar (Micromeritics) connected to a Julabo F32-MC isothermal

bath.* After each isotherm measurement, the sample was evacuated under dynamic vacuum,

until the outgas rate was less than 2 mTorr/min, prior to continuing on to the next measurement.

*The identification of any commercial product or trade name does not imply endorsement or recommendation by the National Institute of Standards and Technology.

Fitting of Isotherms.

The measured experimental pure component isotherms for CO2 and N2, in terms of

excess loadings, were first converted to absolute loadings. The absolute adsorbate loadings were

obtained using the following procedure. The fluid densities at any given temperature were

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determined using the NIST Thermochemical Properties of Fluid Systems.3 Subsequently, these

values were multiplied by the pore volume of each material to obtain the loadings in the “bulk”

of the pore space. The pore volumes of Cu-SSZ-13 and H-SSZ13 used for this purpose were

0.253 cm3/g and 0.272 cm3/g, respectively, based on the N2 adsorption data at 77 K. Addition of

the loadings in the “bulk” to the experimentally determined “excess” loadings yields the

“absolute” component loadings. All isotherm fits, and subsequent analyses to determine

selectivities and isosteric heats of adsorption, were carried out using absolute loadings.

The absolute component loadings were fitted with either a single-site Langmuir model or

dual-site Langmuir model. For N2 adsorption at 298 K, there are no discernible isotherm

inflections in either Cu-SSZ-13 or H-SSZ13, and the single site Langmuir model (Equation 1)

was used for the isotherm fitting. The single-site Langmuir fit parameters are specified in Table

S1.

q =qsatbp

1+ bp (1)

For adsorption of CO2, the dual-site Langmuir model (Equation 2) was used to

individually fit the adsorption data for each material at 298 K, 308 K, and 318 K. The dual-site

Langmuir parameters are specified for Cu-SSZ-13 and H-SSZ-13 in Table S2 and S3,

respectively.

q ≡ qA +qB =qsat,AbA p

1+ bA p+

qsat,BbB p

1+ bB p (2)

IAST Selectivity Calculations.

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In order to determine the selectivity factor, Sads, for binary mixtures using pure

component isotherm data, it is necessary to use an adsorption model, such as ideal adsorbed

solution theory (IAST),4 since collection of experimental data for a mixed component gas cannot

be conveniently and rapidly performed.5 The accuracy of the IAST procedure has already been

established for the adsorption of a wide variety of gas mixtures in different zeolites.6

The IAST estimations of adsorption selectivities for CO2 over N2 were calculated for an

idealized flue gas mixture composed of 0.15 bar CO2 and 0.75 bar N2 to be 72.0 and 73.6 for Cu-

SSZ-13 and H-SSZ-13, respectively. The selectivity factor is defined according to Equation 3

where qi is the molar uptake predicted by IAST based on the fits to the isotherm data and pi is the

partial pressure of component i.

Sads =q1 q2

p1 p2

(3)

Isosteric Heat of Adsorption Calculations.

The Clausius-Clapeyron equation was used to calculate the enthalpies of adsorption for

CO2 on Cu-SSZ-13 and H-SSZ-13, using the dual-site Langmuir fits for each material at 298 K,

308 K, and 318 K,

ln P( )n= Qst R( ) 1 T( )+C

where P is the pressure, n is the amount adsorbed, T is the temperature, R is the universal gas

constant, and C is a constant. The isosteric heat of adsorption, -Qst, was subsequently obtained

from the slope of plots of (ln P)n as a function of 1/T. At low coverage, the isosteric heats of

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adsorption for Cu-SSZ-13 and H-SSZ-13 were calculated to be 33.1 and 34.0 kJ/mol,

respectively (Figure S4).

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Table S1. Single-site Langmuir parameters for adsorption of N2 in Cu-SSZ-13 and H-SSZ-13 at

298 K.

Cu-SSZ-13 H-SSZ-13

qsat (mmol/g) 3.50 3.94

b (bar-1) 0.102 0.0800

Table S2. Dual-site Langmuir parameters for adsorption of CO2 in Cu-SSZ-13 at 298 K, 308 K,

and 318 K.

298 K 308 K 318 K

qsat,A (mmol/g) 1.52 1.31 1.25

bA (bar-1) 14.43 9.96 6.84

qsat,B (mmol/g) 3.64 3.69 3.67

bB (bar-1) 1.77 1.31 0.994

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Table S3. Dual-site Langmuir parameters for adsorption of CO2 in H-SSZ-13 at 298 K, 308 K,

and 318 K.

298 K 308 K 318 K

qsat,A (mmol/g) 1.51 1.34 1.06

bA (bar-1) 12.57 8.63 6.37

qsat,B (mmol/g) 4.24 4.23 4.28

bB (bar-1) 1.56 1.16 1.06

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Figure S1. Experimental data for adsorption of N2 in Cu-SSZ-13 and H-SSZ-13 at 298 K. The continuous solid lines are the single-site Langmuir fits using the parameters specified in Table S1.

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Figure S2. Experimental data for adsorption of CO2 in Cu-SSZ-13 at 298, 308, and 318 K. The continuous solid lines are the dual-site Langmuir fits using the parameters specified in Table S2.

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Figure S3. Experimental data for adsorption of CO2 in H-SSZ-13 at 298, 308, and 318 K. The continuous solid lines are the dual-site Langmuir fits using the parameters specified in Table S3.

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Figure S4. Isosteric heats of adsorption for CO2 in Cu-SSZ-13 (green) and H-SSZ-13 (blue), as obtained from dual-site Langmuir fits to the gas adsorption data collected at 298, 308 and 318 K. Low-coverage -Qst for Cu- and H-SSZ-13 are 33.1 and 34.0 kJ/mol, respectively.

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S3. Diffraction Details.

Neutron scattering measurements were conducted on the high-resolution diffractometers BT1, at

the National Institute of Standards and Technology Center for Neutron Research (NCNR)7, for

bare and CO2 gas-dosed Cu-SSZ-13 and H-SSZ-13. Neutron powder diffraction (NPD)

measurements were completed using a Ge(311) monochromator with a 75º take-off angle,

λ = 2.0787(2) Å, and in-pile collimation of 15 minutes of arc were used. Data were collected

over the range of 1.3–166.3º 2θ with a step size of 0.05º via 32 detectors with the sample at

approximately 4 K. A closed-cycle He refrigerator (CCR) was used for temperature control.

Degassed Cu-SSZ-13 (1.29 g) and H-SSZ-13 (1.01g) samples were transferred into cylindrical

vanadium cans of length 50 mm and diameter 10.8 mm inside a dry He-filled glovebox, sealed

with an In o-ring to a capillary gas line and valve, and mounted to sample sticks equipped with a

stainless-steel gas line with an additional valve for use in the CCR. Residual helium was

removed from the sample at room temperature by use of a turbo-molecular pump prior to neutron

scattering measurements. The process of CO2 loading for the diffraction experiments has been

described previously.8-11 After collecting data on the bare sample, the sample is heated to ca. 250

K and a calculated amount of CO2, based on the total number of metal sites in the sample, is

loaded into a known volume at room-temperature. The volume is opened to the sample and the

gas allowed to equilibrate. The temperature is then slowly decreased to 4 K. The pressure gauge

was monitored to determine that all of the CO2 was adsorbed into the sample.

Additional data were collected on the ECHIDNA instrument, at the Opal research reactor

and operated by the Bragg Institute within the Australian Nuclear Science and Technology

Organisation (ANSTO)12, for bare and N2 gas-dosed Cu-SSZ-13. An evacuated sample of Cu-

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SSZ-13 weighing 0.92 g, was transferred to a vanadium cell in an Ar-filled glovebox. The cell

was equipped with heaters for the gas line and valve to allow rapid uniform sample temperatures

to be reached. The high-intensity diffractometer was configured with a Ge(331) monochromator

using a take-off angle of 140° with no secondary collimation, resulting in a La11B6 callibrated

wavelength of 2.4399 Å. Diffraction data were collected at 10 K for the bare Cu-SSZ-13 and

with a N2 loading of 1.5 N2 per Cu2+. For the nitrogen loading, the cryostat and sample were

heated to 80 K to facilitate adsorption of the 99.999% pure N2 gas.

All NPD data were analyzed using the Rietveld method as implemented in

EXPGUI/GSAS13,14. Synchrotron X-ray diffraction data used as the starting geometry for the

subsequent Rietveld refinements of the Cu-SSZ-13 neutron data,15 with an existing neutron

diffraction derived model used as the starting geometry for the H-SSZ-13 refinements.16 Since

the sample of H-SSZ-13 was not deuterated for the NPD, the incoherent proton background in

the data is more pronounced, resulting in a larger degree of uncertainty in atom positions; in

particular for the weak coherent scattering from H-atom.

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Table S4. Atomic parameters from Rietveld refinement of Cu-SSZ-13 data [NCNR, BT1]

(Trigonal, R-3m, a = 13.5484(6) Å, c = 15.082(1) Å, V = 2397.5(2) Å3). Goodness-of-fit parameter χ2 = 0.986. Composition (Al2.988Si33.012Cu1.543O72.0).

X Y Z Occupancy U(ISO) (ÅÅÅÅ2) Multiplicity

Al -0.0015(7) 0.2290(6) 0.0997(6) 0.083 0.009(2) 36 O1 0.9046(4) 0.0954(4) 0.1166(8) 1 0.044(3) 18 O2 0.9747(6) 0.3081(6) 0.1667 1 0.034(3) 18 O3 0.1220(4) 0.2439(8) 0.1272(8) 1 0.043(3) 18 O4 0 0.2670(6) 0 1 0.028(3) 18 Cu 0 0 0.118(4) 0.25(2) 0.05(2) 6 Si -0.0015(7) 0.2290(6) 0.0997(6) 0.917 0.009(2) 36

Table S5. Atomic parameters from Rietveld refinement of Cu-SSZ-13 at a loading of 0.5 CO2

molecules per Cu2+ site [NCNR, BT1] (Trigonal, R-3m, a = 13.5573(7) Å, c = 15.066(1) Å, V =

2398.1(2) Å3). Goodness-of-fit parameter χ2 = 1.048. The refined composition is (Cu-SSZ-13): 0.57 CO2 per Cu2+.


Al -0.0001(7) 0.2308(6) 0.1006(5) 0.083 0.016(2) 36 O1 0.9039(3) 0.0961(3) 0.1177(6) 1 0.031(3) 18 O2 0.9769(5) 0.3103(5) 0.1667 1 0.020(2) 18 O3 0.1222(3) 0.2444(7) 0.1287(7) 1 0.033(3) 18 O4 0 0.2666(6) 0 1 0.023(2) 18 Cu 0 0 0.121(3) 0.25(2) 0.05(2) 6 Si -0.0001(7) 0.2308(6) 0.1006(5) 0.917 0.016(2) 36 C 0.16667 0.33334 0.33334 0.090(6) 0.01(3) 9

O5 0.120(3) 0.240(6) 0.351(5) 0.090(6) 0.03(3) 18

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Al -0.0012(7) 0.2298(6) 0.1000(5) 0.083 0.011(2) 36 O1 0.9046(4) 0.0954(4) 0.1182(7) 1 0.034(3) 18 O2 0.9766(5) 0.3100(5) 0.1667 1 0.020(2) 18 O3 0.1213(4) 0.2426(7) 0.1279(7) 1 0.036(3) 18 O4 0 0.2662(6) 0 1 0.024(2) 18 Cu 0 0 0.127(3) 0.25(2) 0.07(2) 6 Si -0.0012(7) 0.2298(6) 0.1000(5) 0.917 0.011(2) 36 C1 0.16667 0.33334 0.33334 0.157(7) 0.01(4) 9 O5 0.126(2) 0.251(5) 0.351(4) 0.157(7) 0.04(3) 18





Al 0.0003(7) 0.2296(6) 0.0992(5) 0.083 0.006(2) 36 O1 0.9038(4) 0.0962(4) 0.1179(7) 1 0.033(3) 18 O2 0.9759(6) 0.3093(6) 0.1667 1 0.019(2) 18 O3 0.1214(4) 0.2427(8) 0.1284(7) 1 0.040(3) 18 O4 0 0.2658(6) 0 1 0.026(2) 18 Cu 0 0 0.128(3) 0.25(2) 0.04(2) 6 Si 0.0003(7) 0.2296(6) 0.0992(5) 0.917 0.006(2) 36 C1 0.1667 0.3334 0.3334 0.251(8) 0.03(2) 9 O5 0.117(2) 0.234(4) 0.354(3) 0.251(8) 0.07(2) 18

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Table S8. Atomic parameters for Rietveld refinement for bare H-SSZ-13 [NCNR, BT1]

(Trigonal, R-3m, a = 13.6848(8) Å, c = 15.000(2) Å, V = 2432.7(3) Å3). Goodness-of-fit parameter χ2 = 1.153. The refined composition is Al2.988Si33.012H3.096O83.985.


Al 0.0006(7) 0.2302(5) 0.1012(5) 0.086 0.004(1) 36 O1 0.9013(3) 0.0987(3) 0.1159(5) 1 0.014(2) 18 O2 0.9753(5) 0.3087(5) 0.1667 1 0.014(2) 18 O3 0.1209(4) 0.2417(7) 0.1335(7) 1 0.019(3) 18 O4 0 0.2616(6) 0 1 0.026(2) 18 Si 0.0006(7) 0.2302(5) 0.1012(5) 0.914 0.004(1) 36 H1 -0.03(4) 0.645(3) -0.01(4) 0.04(2) 0.15(2) 36 H2 0.891(9) 0.78(2) 0.81(2) 0.081(3) 0.13(2) 18

Table S9. Atomic parameters for Rietveld refinement for H-SSZ-13 at a loading of 2.0 CO2

molecules per H+ [NCNR, BT1] (Trigonal, R-3m, a = 13.686(2) Å, c = 14.975(2) Å, V = 2428.9(4) Å3). Goodness-of-fit parameter χ2 = 1.032. The refined composition is H-SSZ-13 : 1.94 CO2 per H+.


Al 0.004(1) 0.231(3) 0.1027(7) 0.086 0.003(2) 36 O1 0.9007(4) 0.0993(4) 0.1167(7) 1 0.001(3) 18 O2 0.9787(8) 0.3121(8) 0.1667 1 0.006(3) 18 O3 0.1192(6) 0.238(2) 0.137(2) 1 0.028(5) 18 O4 0 0.264(2) 0 1 0.054(5) 18 Si 0.004(1) 0.231(3) 0.1027(7) 0.914 0.003(2) 36 H1 -0.04(3) 0.063(3) -0.02(3) 0.04 0.2(2) 36 H2 0.9(1) 0.79(2) 0.81(2) 0.081 0.2(2) 18 C1 0.1667 0.3334 0.3334 0.34(1) 0.05(2) 9 O5 0.105(2) 0.211(3) 0.364(2) 0.34(1) 0.09(2) 18

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Table S10. Atomic parameters for Rietveld refinement for an evacuated sample of Cu-SSZ-13

[ANSTO, ECHIDNA] (Trigonal, R-3m, a = 13.5202(5) Å, c = 15.0818(9) Å, V = 2387.5(2) Å3). Goodness-of-fit parameter χ2 = 1.729.


Al 0.0002(5) 0.2290(4) 0.0960(5) 0.086 0.01(2) 36 O1 0.9053(3) 0.0947(3) 0.1153(5) 1 0.040(3) 18 O2 0.9724(4) 0.3058(4) 0.1667 1 0.034(2) 18 O3 0.1213(3) 0.2426(5) 0.1296(5) 1 0.051(3) 18 O4 0 0.2672(4) 0 1 0.016(2) 18 Cu 0 0 0.130(2) 0.26(2) 0.02(2) 6 Si 0.0002(5) 0.2290(4) 0.0960(5) 0.914 0.01(2) 36

Table S11. Atomic parameters for Rietveld refinement for Cu-SSZ-13 at a loading of 1.5 N2

molecules per Cu2+ [ANSTO, ECHIDNA] (Trigonal, R-3m, a = 13.5233(5) Å, c = 15.072(1) Å, V = 2387.1(2) Å3). Goodness-of-fit parameter χ2 = 1.921. The refined composition is Cu-SSZ-13 : 1.38 N2 per Cu2+.


Al -0.0013(6) 0.2258(5) 0.0963(5) 0.086 0.005(1) 36 O1 0.90615(29) 0.09385(29) 0.1153(5) 1 0.017(3) 18 O2 0.9721(5) 0.3055(5) 0.1667 1 0.040(3) 18 O3 0.12109(29) 0.2421(6) 0.1282(6) 1 0.041(3) 18 O4 0 0.2671(4) 0 1 0.054(5) 18 Cu 0 0 0.130(2) 0.26(2) 0.01(1) 6 Si -0.0013(6) 0.2258(5) 0.0963(5) 0.086 0.005(1) 36

N1 0.102(1) 0.204(2) 0.334(2) 0.157(3) 0.033(8) 18 N2 0.078(2) 0.156(4) 0.400(3) 0.079(1) 0.04(1) 36

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Figure S5. Neutron powder diffraction data collected for bare Cu-SSZ-13 at 4K. Green lines, crosses, and red lines represent the background, experimental, and calculated diffraction patterns, respectively. The blue line represents the difference between experimental and calculated patterns. The final Rietveld goodness-of-fit parameter was χ2 = 0.986.

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Figure S6. Neutron powder diffraction data collected for Cu-SSZ-13 loaded with 1.0 CO2 molecules per Cu2+ at 4K. Green lines, crosses, and red lines represent the background, experimental, and calculated diffraction patterns, respectively. The blue line represents the difference between experimental and calculated patterns. The final Rietveld goodness-of-fit parameter was χ2 = 1.071.

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Figure S7. Neutron powder diffraction data collected for Cu-SSZ-13 loaded with 1.5 CO2 molecules per Cu2+ at 4K. Green lines, crosses, and red lines represent the background, experimental, and calculated diffraction patterns, respectively. The blue line represents the difference between experimental and calculated patterns. The final Rietveld goodness-of-fit parameter was χ2 = 1.098.

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Figure S8. Neutron powder diffraction data collected for bare H-SSZ-13 at 4K. Green lines, crosses, and red lines represent the background, experimental, and calculated diffraction patterns, respectively. The blue line represents the difference between experimental and calculated patterns. The final Rietveld goodness-of-fit parameter was χ2 = 1.153.

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Figure S9. Neutron powder diffraction data collected for H-SSZ-13 loaded with 2.0 CO2 molecules per H+ at 4K. Green lines, crosses, and red lines represent the background, experimental, and calculated diffraction patterns, respectively. The blue line represents the difference between experimental and calculated patterns. The final Rietveld goodness-of-fit parameter was χ2 = 1.032.

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Figure S10. Neutron powder diffraction data collected for evacuated (bare) Cu-SSZ-13 loaded at 4K. Green lines, crosses, and red lines represent the background, experimental, and calculated diffraction patterns, respectively. The blue line represents the difference between experimental and calculated patterns. The final Rietveld goodness-of-fit parameter was χ2 = 1.729.

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Figure S11. Neutron powder diffraction data collected for Cu-SSZ-13 loaded with 1.5 N2 molecules per Cu+ at 4K. Green lines, crosses, and red lines represent the background, experimental, and calculated diffraction patterns, respectively. The blue line represents the difference between experimental and calculated patterns. The final Rietveld goodness-of-fit parameter was χ2 = 1.921.

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S4. Describing the CO2/N2 interaction with the 8-ring window.

Interaction of a point quadrupole with the electric field of a charged ring.

Model of the interaction of CO2 with an 8-ring window in a zeolite structure.

If one considers CO2 as a point quadrupole and the 8-ring window as a continuous charged ring of ~ 2Å

in radius,

The energy of interaction of a linear quadrupole Q with an inhomogeneous electric field with potential V

is given by:

εQ =1

2Q∂2

V

∂z2

εQ =1

2Q∂EZ

∂z

EZ =δV

δz

where εQ= energy of quadrupole interaction, Q is magnitude of the linear quadrupole, V is the electric

potential and Ez is the electric field along the z axis, where z is perpendicular to the plane of the a

charged ring or radius r=a.

For a charged ring, along the axis of the ring:

EZ=

kqz

z2 + a

2( )3

2

δEz

δz= kq

1

z2 + a2( )3

2−

3z2

z2 + a2( )5

2

where q is the total charge on the ring, k is the reciprocal of 4πe0 (electric permittivity in vacuum) and

the plot of the electric field gradient then gives Figure S11, for a=2 Å.

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Figure S12. Plot of the electric field gradient a a function of distance from the center of the ring.

This means there is a minimum energy for a positive Q, and a negatively charged ring sin(q)=-1 at

the center of the ring, that there is a small activation energy to reach this position, and that the

minimum is sharp. Based on the above equations to maximize the energy we need to reduce the radius

of the ring a or maximize the charge on the ring q. The charge on the ring can be, in principle, increased

by decreasing the Si/Al ratio of the zeolite, however, the size of the zeolite pore cannot physically be

reduced below an 8-ring based on the dimensions of the CO2 molecule and the available space in the

window.

This also means that there is maximum energy for a negative Q. Consequently, molecules such as

H2, C2H4 and C2H2 will be ‘repelled’ by the 8-ring windows. This may be good or bad depending on the

target situation. For the case of CO2 and N2, both have a quadrupole of the same sign (-14.3 x 10-40 C m2

and -4.6 x 10-40 C m2, respectively) so both are attracted to the center of the 8-ring window by varying

strengths.

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Competition between dipole and quadrupole forces

One of the interesting qualities of the 8-ring window revealed by this model is that it is selective for

molecules with quadrupoles and that molecules with large dipole moments, but weak quadrupole

moments, are not attracted to it. This can be seen in Figure S12 where the energy between an electric

field and a dipole aligned along the ring centerline is plotted. Here we can see that the minimum energy

position for a dipole is not at the center of the ring, but away of the center of the ring by a distance

r/sqrt(2). Note that in this graph the electric field is asymmetric, but the energy would be symmetric

because the dipole would rotate immediately to keep the positive end of the dipole close to the ring.

Figure S13. Plot of the electric field gradient and the electric field at the centerline of a charged ring of

2Å in diameter. x = electric field gradient, + = electric field. Note that the two axes are different and

that the electric field is antisymmetric around the origin.

S31

DFT Calculations.

DFT single-point energies were calculated using a 6-311g(d,p) basis set at fixed integer steps (10 degrees) for small gas molecules passing through an isolated 8-ring window of SSZ-13 using the GAUSSIAN03 (rev. E06)17 software program to determine the rough affinity for adsorption in or near the ring window. As with the point-charge description of the 8-ring window, there is a preference for CO2 and N2 in the window (with the N2 also exhibiting a second energy minima at 120°) and small hydrocarbons and H2 being energetically opposed (energy maxima) to locating in the center of the window.

S32

Figure S14. Plot of potential energy (in a.u.) as a function of angle (in degrees) out of the plane of the 8-ring window for the “ideal” geometry of CO2.

-46.5 kJ/mol

-8.0 kJ/mol

S33

Figure S15. Plot of potential energy (in a.u.) as a function of angle (in degrees) out of the plane of the 8-ring window for the “ideal” geometry of N2.

Figure S16. Plot of potential energy (in a.u.) as a function of angle (in degrees) out of the plane of the 8-ring window for the “ideal” geometry of H2.

-1.7 kJ/mol

73.6 kJ/mol

S34

Figure S17. Plot of potential energy (in a.u.) as a function of angle (in degrees) out of the plane of the 8-ring window for the “ideal” geometry of C2H2.

Figure S18. Plot of potential energy (in a.u.) as a function of angle (in degrees) out of the plane of the 8-ring window for the “ideal” geometry of C2H4.

1.7 kJ/mol

4.2 kJ/mol

S35



-170.7 kJ/mol

S36

S5. References.

(1) Zones, S. I. U.S. Patent 4,544,538, 1985. (2) Zones, S. J. Chem. Soc., Faraday Trans. 1991, 87, 3709. (3) Lemmon, E. W.; McLinden, M.O.; Friend, D. G. Thermophysical Properties of Fluid Systems. In NIST

Chemistry WebBook, NIST Standard Reference Database Number 69: Linstrom, P. J.; Mallard, W. G., Eds.; National Institute of Standards and Technology: Gaithersburg MD. 2010.

(4) Meyers, A. L.; Prausnitz, J. M. AIChE J. 1965, 11, 121. (5) Talu, O. Adv. Colloid Interface Sci. 1998, 76-77, 227. (6) (a) Krishna, R.; Calero, S.; Smit, B. Chem. Eng. J. 2002, 88, 81. (b) Krishna, R.; van Baten, J. M. Chem.

Eng. J. 2007, 133, 121. (7) http://www.ncnr.nist.gov/ (8) Brown, C.; Liu, Y.; Neumann, D. Pramana 2008, 71, 755. (9) Brown, C.; Liu, Y.; Yildirim, T.; Peterson, V.; Kepert, C. Nanotechnology 2009, 20, 204025. (10) Peterson, V. K.; Liu, Y.; Brown, C. M.; Kepert, C. J. J. Am. Chem. Soc. 2006, 128, 15578. (11) Sumida, K.; Horike, S.; Kaye, S. S.; Herm, Z. R.; Queen, W. L.; Brown, C. M.; Grandjean, F.; Long, G.

J.; Dailly, A.; Long, J. R. Chem. Sci. 2010, 1, 184. (12) Liss, K.-D.; Hunter, B.; Hagen, M.; Noakes, T.; Kennedy, S. Physica B: Conden. Mat., 2006, 385-386,

1010. (13) A.C. Larson and R.B. Von Dreele “General Structure Analysis System (GSAS)”, Los Alamos National Laboratory Report LAUR, 1994, 86. (14) Toby, B. J. Appl. Crystallogr. 2001, 34, 210. (15) Fickel, D.; Lobo, R. J. Phys. Chem. C 2009, 114, 1633. (16) Smith, L.; Davidson, A.; Cheetham, A. Catal. Lett. 1997, 49, 143. (17) Gaussian 03, Revision E.06., Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;

Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong,

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