Highly Selective Sorption and Separation of CO2 from a Gas Mixture

Article pubs.acs.org/JPCC

Highly Selective Sorption and Separation of CO2 from a Gas Mixture of CO2 and CH4 at Room Temperature by a Zeolitic Organic− Inorganic Ionic Crystal and Investigation of the Interaction with CO2 Ryo Eguchi, Sayaka Uchida,† and Noritaka Mizuno* Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan S Supporting Information *

ABSTRACT: Mixed gas cosorption and gas chromatographic investigations demonstrate that a zeolitic organic−inorganic ionic crystal K2[Cr3O(OOCH)6(4-etpy)3]2[α-SiW12O40]·2H2O [1·2H2O] (etpy = ethylpyridine) with a pore diameter of 3.5 Å possesses high separation ability of carbon dioxide (kinetic diameter 3.3 Å) over methane (3.76 Å) at room temperature in the presence of water vapor. Monte Carlo simulation combined with density functional theory calculation suggests that carbon dioxide molecules diffuse into the one-dimensional channels and interact initially with the potassium ions and then with the oxygen atoms of silicododecatungstates, which are confirmed with carbon dioxide sorption enthalpy and in situ IR spectroscopy.

1. INTRODUCTION Carbon dioxide (CO2) separation is currently of great importance in terms of environmental protection and industrial processes.1 Especially, separation of CO2 from a gas mixture of CO2 and methane (CH4) is an essential process for natural gas purification and landfill-gas separation.2 Amine solutions have commonly been used to capture CO2 (chemical absorption),1 while these processes possess critical disadvantages such as toxicity, corrosiveness, and high energy for regeneration. Therefore, environmentally friendly and economically feasible techniques are required. Porous materials are promising alternatives for the CO2 separation because physical adsorption is energetically more efficient compared with chemical absorption. Zeolites have been studied as CO2 adsorbents, while the separation ability is low, high temperature (>573 K) is required for regeneration, and adsorption capacity is strongly reduced by the presence of a small amount of water vapor (1.4 wt %).3 Metal organic frameworks (MOFs) have also been studied as CO2 adsorbents, and high CO2 adsorption capacity and separation ability are achieved by the adjustment of pore sizes,4 basic, open metal, and polar sites,5−8 and unique structural flexibilities,9,10 while some MOFs are unstable under humid conditions.11−13 Since water vapor is usually contained in natural gas and other industrial gas resources, stability of adsorbents toward the water vapor is an important factor. Various porous materials have been reported as adsorbents for the separation of CO2 from a gas mixture of CO2 and CH4 (Table S1), but there are only a few reports demonstrating gas separation ability in the presence of water vapor.14−17 Polyoxometalates (POMs) are anionic nanosized metal− oxygen clusters and suitable inorganic building blocks to form nanostructured compounds because of their discrete structures © 2012 American Chemical Society

and interesting acid−base, redox, and photochemical properties.18 Therefore, complexation of POMs with appropriate molecular cations can create functional materials with structural diversities.19−24 We have recently reported the structure and gas sorption properties of a flexible organic−inorganic ionic crystal of K2[Cr3O(OOCH)6(4-etpy)3]2[α-SiW12O40] (etpy = ethylpyridine) [1].25 Structural flexibility and strong electrostatic field that are characteristic of organic−inorganic ionic crystals enable the highly selective sorption of CO2 over acetylene (C2H2) with very similar physical properties. However, high temperature (373 K) was needed for the complete desorption of solvent and guest molecules and the reuse of 1. While continuing our research on this system, we have found out that the treatment of K2[Cr3O(OOCH)6(4etpy)3]2[α-SiW12O40]·6H2O [1·6H2O] in vacuo or under dry N2 or He gases at room temperature forms a rigid porous (i.e., zeolitic) ionic crystal K2[Cr3O(OOCH)6(4-etpy)3]2[α-SiW12O40]·2H2O [1·2H2O] with a pore diameter of 3.5 Å (Figures S1−S4). In this paper we report that 1·2H2O shows highly selective sorption and separation of CO2 from a gas mixture of CO2 and CH4 even at room temperature and investigate the interaction of 1·2H2O and CO2.

2. EXPERIMENTAL SECTION 2.1. Syntheses of 1·4CH3OH, 1·6H2O, and 1·2H2O. In 100 mL of 1,2-dichloroethane, [Cr 3 O(OOCH) 6 (4ethylpyridine)3](ClO4)·nH2O (0.50 g) was dissolved. To this solution, CH3COOK (0.50 g) dissolved in a minimum amount Received: June 15, 2012 Revised: July 10, 2012 Published: July 10, 2012 16105

dx.doi.org/10.1021/jp305890s | J. Phys. Chem. C 2012, 116, 16105−16110

The Journal of Physical Chemistry C

Article

of methanol (ca. 2 mL) was added followed by filtration to remove KClO4 (solution A). In 200 mL of methanol, H4SiW12O40·nH2O (0.75 g) and CH3COOK (0.50 g) were dissolved (solution B). Solution B was added to solution A with vigorous stirring, and the resulting solution was kept at room temperature for 24 h. Brown crystals of 1·4CH3OH were isolated in ca. 60% yield. Details of the crystal structure of 1·4CH3OH have been reported in ref 25. Compound 1·4CH3OH spontaneously transformed into 1·6H2O under an ambient atmosphere (298 K and P/P0 = 0.4) without any structure changes. FT-IR: 1641 (br, νasym(CO2)), 1378 (m, νsym(CO2)), 972 (m, νasym(WOt)), 924 (s, νasym(Si−O)), 887 (w, νasym(W−Oc−W)), 803 (br, νasym(W−Oe−W)), 636 (m, νasym(Cr3O)) cm−1. Elemental analysis calcd. for 1·6H2O: C 14.14, H 1.71, N 1.83, Cr 6.80, K 1.70, Si 0.61, W 48.09; found: C 14.48, H 1.80, N 1.75, Cr 6.96, K 1.75, Si 0.63, W 48.28. The mass (MS) spectra of 1·6H2O under a dry He flow at 303 K for 3 h showed that water (HO: m/z = 17 and H2O: m/z = 18) existed while methanol (CH3O: m/z = 31) did not exist (Figure S1). Thermogravimetry (TG) showed that 4 mol mol−1 of water (weight loss of 1.8 wt %) was desorbed by the treatment to form 1·2H2O. The TG-MS spectra of 1·2H2O under a dry He flow at 303−773 K showed the existence of 2 mol mol−1 of water, and these water molecules were completely desorbed at 373 K (weight loss of 0.8 wt %; Figure S2), while the in situ powder XRD measurement indicated a structure change after the treatment. 2.2. TG-MS Measurements. TG measurements were performed with a Thermo Plus 2 thermogravimetric analyzer (Rigaku Corp.) using α-Al2O3 as a reference under a dry He flow (250 mL min−1). Gases at the outlet were analyzed with a GCMS-QP5050 instrument (Shimadzu). 2.3. Powder XRD Measurements. Powder XRD patterns were measured with a XRD-DSCII (Rigaku Corp.) by using Cu Kα radiation (λ = 1.540 56 Å, 50 kV−300 mA) at 298−303 K. Diffraction data were collected in the range of 2θ = 3°−20° at 0.01° point and 5 s step−1. The measurements for 1·6H2O and 1·2H2O were carried out under an ambient atmosphere and a dry N2 flow, respectively. 2.4. CO2 Sorption Kinetics and Gas Sorption Measurements. About 20 mg of 1·6H2O was treated under a dry He flow at 306 K for 3 h to form 1·2H2O. The amounts of CO2 sorption were measured at 306 K with a Thermo Plus 2 thermogravimetric analyzer (Rigaku Corp.) using α-Al2O3 as a reference. Experimental profiles were fitted with the Fickian diffusion model26 and the least-squares method. The average particle radius of 1·2H2O obtained from microscopic images was 4.5 × 10−3 cm (Figure S5). Sorption isotherms of N2, O2, CO2, and CH4 were measured with a Belsorp instrument (BEL Japan Inc.). About 0.15 g of 1·6H2O was treated in vacuo at 303 K for 3 h to form 1·2H2O. The sorption equilibrium was judged by the following criteria: ±0.3% of pressure change in 5 min. 2.5. Mixed Gas Cosorption Measurements. Measurements were carried out with a Belsorp-VC instrument (BEL Japan Inc.). About 1.0 g of 1·6H2O was treated in vacuo at 303 K for 3 h to form 1·2H2O. A gas mixture of CO2 and CH4 (with or without 0.1 wt % of water vapor) was exposed to 1·2H2O. After reaching equilibrium (ca. 3 h), the sorbed amount of each gas was estimated based on the volumetric method by the analysis of the gases before and after the exposure by a micro gas chromatograph.

2.6. Gas Chromatographic (GC) Separation of CO2 and CH4. GC separation of a gas mixture of CO2 and CH4 using a column packed with 1·2H2O was performed with a Shimadzu GC-8A system equipped with a thermal conductivity detector. Crystals of 1·6H2O were well ground, and about 3.9 g of 1·6H2O was densely packed into the column. The fresh column of 1·6H2O was treated at room temperature by introducing a carrier gas (20 mL min−1 of a dry He flow) for more than 5 h to form 1·2H2O. The gas mixture (CO2/CH4 = 1.4:1.0 mol % with or without 3 wt % of water vapor) was injected, and the separation was carried out at room temperature. 2.7. In situ IR Spectroscopy. Compound 1·6H2O was dispersed in n-hexane, spread on a Si plate, and allowed to airdry. The Si plate was placed into a IR cell followed by the treatment in vacuo at 298 K for 3 h to form 1·2H2O. Then, a CO2 gas was introduced into the cell under controlled temperature, and IR spectra were measured with a FT-IR 460 Plus spectrometer (Jasco). The in situ IR spectrum of CO2 molecules sorbed in 1·2H2O was obtained by the subtraction of the spectra of 1·2H2O and CO2 gas from the raw spectrum. An argon gas was purged around the IR cell during the experiments because atmospheric CO2 concentration fluctuates in open systems. 2.8. Monte Carlo (MC) Simulations and Density Functional Theory (DFT) Calculations. MC simulations were carried out using the Sorption tool of Material Studio package (Accelrys Inc.) by the Metropolis MC method with universal force field.27,28 The crystal structure of 1·4CH3OH was used as a host after the removal of methanol molecules. Prior to MC simulations of CO2 sorption, the locations of the 2 mol mol−1 of water molecules in 1·6H2O were optimized. Geometrically optimized water molecules existed in the vicinity of potassium ions (K−O: ca. 2.56−2.73 Å; Figure S4). Positions of all atoms of the framework (silicododecatungstate, macrocation, and K+) and water molecules were fixed during the simulations. The reported bond length (1.16 Å) and partial atomic charges of CO2 (C = +0.70e, O = −0.35e)29 were used. Partial atomic charges of the framework and water molecules were derived from the DFT calculations as follows: (1) Template structures (silicododecatungstate and macrocation) were cut out from the crystal structure. (2) Geometrical optimization and ESP charge analysis30,31 were carried out using the Dmol3 tool32 of Materials studio package. DFT calculations were carried out at the B3LYP33 level theory with 6-311+G(d) basis sets for C and O atoms, 6-311G(d) for Si and K atoms, and the LanL2TZ(f) basis sets with effective core potentials proposed by Hay and Wadt34 for W atoms. The binding energies (Ebind) were calculated by Ebind = E(host·CO2) − E(host) − E(CO2) utilizing the counterpoise technique of Boys and Bernardi35 that corrects the basis set superposition error. These calculations were performed with the Gaussian09 program package.36

3. RESULTS AND DISCUSSION The gas sorption isotherms showed that 1·2H2O sorbed CO2 (kinetic diameter 3.3 Å),2 while CH4 (3.76 Å),2 N2 (3.64 Å),2 and O2 (3.46 Å)2 were excluded, showing size selectivity (Figure 1a and Figure S6). The sorption isotherm of CO2 belonged to type I (IUPAC classification) characteristic of microporous compounds. The BET surface area and micropore volume were 47 m2 g−1 and 1.8 molecules of CO2 per formula, respectively. 16106



Article

gas (50: 50) with or without water vapor.38 Under all experimental conditions, CO2 was more preferably sorbed over CH4 regardless of the existence of the water vapor. The separation selectivities (SCO2/CH4)39 of 1·2H2O were among 10−27, which were higher than or comparable to those previously reported (3−20) (Table S2). The SCO2/CH4 values have usually been calculated based on the ideal adsorbed solution theory (IAST)40 treating each gas component as being ideal and single component isotherms. It is well-known that IAST does not work well at high pressures and loadings,41 and there are only a few reports14−17 demonstrating gas separation ability from an actual gas mixture because of the experimental difficulties in the qualitative and quantitative analyses of a multicomponent gas mixture. High SCO2/CH4 values of 1·2H2O at room temperature show the appropriate separation ability of CO2 over CH4. Furthermore, 1·2H2O was successfully applied to the gas chromatographic separation of CO2 from a gas mixture of CO2 and CH4. The gas mixture was injected into a gas chromatograph equipped with a Pyrex glass column filled with 1·2H2O. As shown in Figure 2, CO2 and CH4 were separated within a

Figure 1. (a) CO2 (square) and CH4 (circle) sorption isotherms of 1·2H2O at 195 K. The solid and open squares showed the sorption and desorption branches, respectively. (b) Changes in the amount of CO2 sorbed by 1·2H2O as a function of time (306 K, 100 kPa). The open circles and solid line showed the experimental and calculated data, respectively.

The time course of the CO2 sorption of 1·2H2O is shown in Figure 1b. The amounts of sorption increased and leveled off after about 600 s. The fitting was carried out with the Fickian diffusion model,26 which has been typically used for diffusion in micropores. The experimental data were well reproduced by the calculation using an average particle radius (d) of 4.5 × 10−3 cm (Figure S5) and a diffusion coefficient (D) of 1.7 × 10−8 cm2 s−1. The diffusion coefficient of CO2 in 1·2H2O was smaller than those of zeolite 5A (pore diameter 5 Å, D = 2.65 × 10−7 cm2 s−1) and MOF-5 (pore diameter 7.7 Å, D = 1.17 × 10−5 cm2 s−1).37 This is probably because of the smaller channel aperture of 1·2H2O (3.5 Å). The separation ability of CO2 over CH4 was investigated by the cosorption measurement with a gas mixture of CO2 and CH4 at 298 K (total pressure of ca. 500 kPa) (Table 1). To evaluate the separation ability, the CO2/CH4 compositions were adjusted to those of typical natural gas (10: 90) or landfill

Figure 2. Gas chromatograms of gas mixture of CO2 and CH4 separated on a column of 1·2H2O: (a) without and (b) with the presence of water vapor (3 wt %).

few minutes at room temperature. Notably, CO2 and CH4 were also separated even in the presence of water vapor. The column could be reused without significant loss of the separation performance (Figure S7). MC simulations combined with DFT calculations were carried out to investigate the CO2 sorption states in 1·2H2O. Typical CO2 geometries sorbed in 1·2H2O obtained with MC simulations are shown in Figure 3a. CO2 molecules were found in the one-dimensional channels and resided either in the vicinity of potassium ions or surface oxygen atoms of silicododecatungstates. To investigate the nature of CO2 binding in more detail, models were cut out from the MCbased geometries and further optimized by DFT calculations.

Table 1. CO2/CH4 Cosorption Measurements of 1·2H2O run

injected gas (CO2:CH4)

sorbed gas (CO2:CH4)

amountc [mol mol−1]

SCO2/CH4

1 2a 3 4a

47:53 52:48 10:90 11:89

96:4 95:4b 63:37 53:45b

1.4 1.6 1.0 1.4

27 22 15 10

a 0.1 wt % H2O vapor was added to the injected gas. b1% and 2% of H2O vapor were sorbed in run 2 and 4, respectively. cTotal amounts of sorption (CO2 + CH4 + H2O).

16107



Article

Table 2. Calculated Binding Energies (Ebind) and IR Frequencies of the Asymmetric Stretching Band of CO2 model

Ebind [kJ mol−1]

freq [cm−1]a,b

1 2 3

18 17 36

2334 2342 2364

a

Scaling factor of 0.97 was used. bFrequency of a free CO2 molecule calculated at the same theoretical level was 2347 cm−1.

Figure 3. (a) Typical MC-based optimized geometries of CO2 sorbed in 1·2H2O. Green and orange molecules showed silicododecatungstates and macrocations, respectively. Purple spheres showed potassium ions. Gray and red spheres showed carbon and oxygen atoms of CO2, respectively. Geometrically optimized 2 mol mol−1 of water were omitted for clarity. DFT-based optimized geometries of (b) silicododecatungstate and (c) potassium ion interacting with CO2. Small dark green and large light green spheres in the silicododecatungstate showed oxygen and tungsten atoms, respectively. The Si atom (light green sphere) was located at the center of the silicododecatungstate. Local structures of (d) model 1 and (e) model 2. Optimized bond lengths (Å) are shown in the figures. Figure 4. (a) CO2 isotherms of 1·2H2O at 278 K (diamond), 283 K (triangle), 298 K (circle), and 303 K (square). (b) Experimental CO2 sorption enthalpy calculated with the Clausius−Clapeyron equation.

Geometrically optimized models are shown in Figure 3b−e. In model 1, CO2 was located near an oxygen atom linking two edge-sharing WO6 units (Oe; Figures 3b,d). In model 2, CO2 was located near an oxygen atom linking two corner-sharing WO6 units (Oc; Figures 3b,e). Notably, a model in which CO2 is interacting only with a terminal oxygen atom (Ot) was not obtained, probably because of the inaccessibility of CO2 due to the steric hindrance within the crystal lattice. In model 3, CO2 was in the vicinity of potassium ions (K−O = 2.671 Å, Figure 3c). The calculated binding energies of CO 2 onto the silicododecatungstate and potassium ions were 17−18 and 36 kJ mol−1, respectively (Table 2). The experimental CO2 sorption enthalpies were calculated with the sorption isotherms measured at different temperatures (278−298 K) with the Clausius−Clapeyron equation (Figure 4). The initial CO2 sorption enthalpy was about 40 kJ mol−1, and the value fairly agreed with the calculated binding energy of CO2 onto potassium ions (36 kJ mol−1). Then, the CO2 sorption enthalpy gradually decreased with increase in the amounts of the CO2 sorption. These results suggest that CO2 molecules initially

interact with the potassium ions and then with the oxygen atoms of silicododecatungstates during the diffusion. The in situ IR spectrum of CO2 sorbed in 1·2H2O (202 K, 5.33 kPa) (νas(OCO) region) showed two bands at 2356 and 2331 cm−1 (Figure S8), and these positions were different from that of gaseous CO2 (2349 cm−1).42 The νas(OCO) band of CO2 is shifted to the higher wavenumber (ca. 2360 cm−1) by interaction with countercations of microporous zeolites.43,44 Therefore, the band at 2356 cm−1 is assigned to the νas(OCO) band of CO2 interacting with potassium ions in the onedimensional channels. On the other hand, the νas(OCO) band of CO2 is shifted to the lower wavenumber by electrostatic interaction with basic sites.45 Therefore, the band at 2331 cm−1 is assigned to the νas(OCO) band of CO2 interacting with the basic surface oxygen atoms of silicododecatungstates. Fair agreement between the calculated νas(OCO) frequencies in models 1−3 with the experimental ones supports this idea (Table 2). 16108



Article

(8) Lee, J. Y.; Roberts, J. M.; Farha, O. K.; Sarjeant, A. A.; Scheidt, K. A.; Hupp, J. T. Inorg. Chem. 2009, 48, 9971. (9) Llewellyn, P. L.; Bourrelly, S.; Serre, C.; Filinchuk, Y.; Férey, G. Angew. Chem., Int. Ed. 2006, 45, 7751. (10) Fukushima, T.; Horike, S.; Inubushi, Y.; Nakagawa, K.; Kubota, Y.; Takata, M.; Kitagawa, S. Angew. Chem., Int. Ed. 2010, 49, 4820. (11) Greathouse, J. A.; Allendorf, M. D. J. Am. Chem. Soc. 2006, 128, 10678. (12) Li, Y.; Yang, R. T. Langmuir 2007, 23, 12937. (13) Liang, Z.; Marshall, M.; Chaffee, A. L. Energy Fuels 2009, 23, 2785. (14) Kauffman, K. L.; Culp, J. T.; Allen, A. J.; Espinal, L.; Wong-Ng, W.; Brown, T. D.; Goodman, A.; Bernardo, M. P.; Pancoast, R. J.; Chirdon, D.; Matranga, C. Angew. Chem., Int. Ed. 2011, 50, 10888. (15) Barea, E.; Tagliabue, G.; Wang, W. G.; Pérez-Mendoza, M. J.; Mendez-Liñan, L.; López-Garzon, F. J.; Galli, S.; Masciocchi, N.; Navarro, J. A. R. Chem.Eur. J. 2010, 16, 931. (16) Couck, S.; Denayer, J. F. M.; Baron, G. V.; Rémy, T.; Gascon, J.; Kapteijn, F. J. Am. Chem. Soc. 2009, 131, 6326. (17) Hamon, L.; Jolimaître, E.; Pirngruber, G. D. Ind. Eng. Chem. Res. 2010, 49, 7497. (18) Hill, C. L., Ed.; Special Thematic Issue on Polyoxometalates. Chem. Rev. 1998, 98, 1. (19) Pradeep, C. P.; Long, D. L.; Cronin, L. Dalton Trans. 2010, 39, 9443. (20) Todea, A. M.; Merca, A.; Bögge, H.; Glaser, T.; Pigga, J. M.; Langston, M. L. K.; Liu, T.; Prozorov, R.; Luban, M.; Schröder, C.; Casey, W. H.; Müller, A. Angew. Chem., Int. Ed. 2010, 49, 514. (21) Noro, S.; Tsunashima, R.; Kamiya, Y.; Uemura, K.; Kita, H.; Cronin, L.; Akutagawa, T.; Nakamura, T. Angew. Chem., Int. Ed. 2009, 48, 8703. (22) Mal, S. S.; Kortz, U. Angew. Chem., Int. Ed. 2005, 44, 3777. (23) Vasylyev, M. V.; Neumann, R. J. Am. Chem. Soc. 2004, 126, 884. (24) Uchida, S.; Eguchi, R.; Mizuno, N. Angew. Chem., Int. Ed. 2010, 49, 9930. (25) Eguchi, R.; Uchida, S.; Mizuno, N. Angew. Chem., Int. Ed. 2012, 51, 1635. (26) Crank, J. The Mathematics of Diffusion; Oxford University Press: London, 1956. (27) Metropolis, N.; Rosenbluth, A. W.; Rosenbluth, M. N.; Teller, A. H.; Teller, E. J. Chem. Phys. 1953, 21, 1087. (28) Rappé, A. K.; Casewit, C. J.; Goddard, W. A., III; Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024. (29) Demet Akten, E.; Siriwardane, R.; Sholl, D. S. Energy Fuels 2003, 17, 977. (30) Chandra Singh, U.; Kollman, P. A. J. Comput. Chem. 1984, 5, 129. (31) Besler, B. H.; Merz, K. M.; Kollman, P. A. J. Comput. Chem. 1990, 11, 431. (32) Delley, B. J. Chem. Phys. 2000, 113, 7756. (33) Becke, A. D. J. Chem. Phys. 1993, 98, 1372. (34) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (35) Boys, S. B.; Bernardi, F. Mol. Phys. 1970, 19, 553. (36) Frisch, M. J.; et al. Gaussian 09; Gaussian, Inc.: Wallingford, CT, 2009. (37) Saha, D.; Bao, Z.; Jia, F.; Deng, S. Environ. Sci. Technol. 2010, 44, 1820. (38) Bae, Y. S.; Snurr, R. Q. Angew. Chem., Int. Ed. 2011, 50, 11586. (39) The separation selectivity is calculated by Si/j = (xi/xj)/(yi/yj), where x and y are the molar fraction of the sorbed phase and gas phase, respectively, for components i and j. (40) Crittenden, J. C.; Luft, P.; Hand, D. W.; Oravitz, J. L.; Loper, S. W.; Ari, M. Environ. Sci. Technol. 1985, 19, 1037. (41) Goj, A.; Sholl, D. S.; Aken, E. D.; Kohen, D. J. Phys. Chem. B 2002, 106, 8367. (42) NIST Standard Reference Database (http://webbook.nist.gov/ chemistry/). (43) Ward, J. W.; Habgood, H. W. J. Phys. Chem. 1966, 70, 1178. (44) Bülow, M. Adsorption 2002, 8, 9.

4. CONCLUSION Mixed gas cosorption and gas chromatographic investigations demonstrated that a zeolitic organic−inorganic ionic crystal 1·2H2O with a pore diameter of 3.5 Å possessed high separation ability of CO2 (kinetic diameter 3.3 Å) over CH4 (3.76 Å) at room temperature even in the presence of water vapor. MC simulations combined with DFT calculations suggested that CO2 molecules diffused into the one-dimensional channels and initially interacted with the potassium ions and then with the oxygen atoms of silicododecatungstates, which was confirmed with CO2 sorption enthalpy and in situ IR spectroscopy.

■

ASSOCIATED CONTENT

S Supporting Information *

Table S1: CO2 and CH4 sorption by various materials; Table S2: CO2/CH4 separation selectivities of various materials; Figure S1: MS spectra of 1·6H2O; Figure S2: TG-MS spectra of 1·2H2O; Figure S3: powder XRD patterns of 1·4CH3OH, 1·6H2O, and 1·2H2O; Figure S4: crystal structure of 1·2H2O; Figure S5: microscopic images of particles of 1·2H2O; Figure S6: N2 and O2 sorption isotherms of 1·2H2O; Figure S7: gas chromatogram of gas mixture of CO2 and CH4 separated on 1·2H2O (third time of use); Figure S8: in situ IR spectrum of CO2 sorbed in 1·2H2O; X-ray data of 1·4CH3OH in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address †

Department of Basic Sciences, School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported in part by the Japan Society for the Promotion of Science (JSPS) through its Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program), the Development in a New Interdisciplinary Field Based on Nanotechnology and Materials Science Programs, and Grant-in-Aids for Scientific Research from the Ministry of Education, Culture, Science, Sports, and Technology of Japan.

■

REFERENCES

(1) D’Alessandro, D. M.; Smit, B.; Long, J. R. Angew. Chem., Int. Ed. 2010, 49, 6058. (2) Li, J. R.; Kuppler, R. J.; Zhou, H. C. Chem. Soc. Rev. 2009, 38, 1477. (3) Brandani, F.; Ruthven, D. M. Ind. Eng. Chem. Res. 2004, 43, 8339. (4) Dybtsev, D. N.; Chun, H.; Yoon, S. H.; Kim, D.; Kim, K. J. Am. Chem. Soc. 2004, 126, 32. (5) Vimont, A.; Travert, A.; Bazin, P.; Lavalley, J. C.; Daturi, M.; Serre, C.; Férey, G.; Bourrelly, S.; Llewellyn, P. L. Chem. Commun. 2007, 3291. (6) Moon, H. R.; Kobayashi, N.; Suh, M. P. Inorg. Chem. 2006, 45, 8672. (7) Britt, D.; Furukawa, H.; Wang, B.; Glover, T. G.; Yaghi, O. M. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 20637. 16109



Article

(45) Culp, J. T.; Goodman, A. L.; Chirdon, D.; Sankar, S. G.; Matranga, C. J. Phys. Chem. C 2010, 114, 2184.

16110


Highly Selective Sorption and Separation of CO2 from a Gas Mixture

Recommend Documents