unconventional and highly selective co adsorption in ... · using the micromeritics software....
TRANSCRIPT
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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
S3
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+.
X Y Z Occupancy U(ISO) (ÅÅÅÅ2) Multiplicity
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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Table S6. Atomic parameters from Rietveld refinement of Cu-SSZ-13 at a loading of 1.0 CO2
molecules per Cu2+ site [NCNR, BT1] (Trigonal, R-3m, a = 13.5572(6) Å, c = 15.066(1) Å, V =
2398.1(2) Å3). Goodness-of-fit parameter χ2 = 1.071. The refined composition is (Cu-SSZ-13): 0.91 CO2 per Cu2+.
X Y Z Occupancy U(ISO) (ÅÅÅÅ2) Multiplicity
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
Table S7. Atomic parameters from Rietveld refinement of Cu-SSZ-13 at a loading of 1.5 CO2
molecules per Cu2+ site [NCNR, BT1] (Trigonal, R-3m, a = 13.557(3) Å, c = 15.060(7) Å, V =
2397.1(1) Å3). Goodness-of-fit parameter χ2 = 1.098. The refined composition is (Cu-SSZ-13): 1.48 CO2 per Cu2+.
X Y Z Occupancy U(ISO) (ÅÅÅÅ2) Multiplicity
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.
X Y Z Occupancy U(ISO) (ÅÅÅÅ2) Multiplicity
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+.
X Y Z Occupancy U(ISO) (ÅÅÅÅ2) Multiplicity
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.
X Y Z Occupancy U(ISO) (ÅÅÅÅ2) Multiplicity
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+.
X Y Z Occupancy U(ISO) (ÅÅÅÅ2) Multiplicity
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.
S22
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.
S23
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.
S24
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.
S25
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.
S26
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.
S27
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.
S29
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.
S30
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
Figure S19. 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.
Figure S20. 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.
-170.7 kJ/mol
S36
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