Highly Selective and Reversible Sulfur Dioxide Adsorption on a

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Highly Selective and Reversible Sulfur Dioxide Adsorption on a Microporous Metal-organic Framework via Polar Sites Yan Zhang, Peixin Zhang, Weikang Yu, Jinghan Zhang, Jiejing Huang, Jun Wang, Mai Xu, Qiang Deng, Zhe ling Zeng, and Shuguang Deng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b01423 • Publication Date (Web): 26 Feb 2019 Downloaded from http://pubs.acs.org on March 2, 2019

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ACS Applied Materials & Interfaces

Highly Selective and Reversible Sulfur Dioxide Adsorption on a Microporous Metal-organic Framework via Polar Sites

Yan Zhang1,2, Peixin Zhang1,2, Weikang Yu1,2, Jinghan Zhang1,2, Jiejing Huang1,2, Jun Wang1,2*, Mai Xu3, Qiang Deng1,2, Zheling Zeng1,2, Shuguang Deng 1, 2, 3*

1Poyang Lake Key Laboratory of Environment and Resource Utilization (Nanchang University), Ministry of Education, Nanchang 330031, Jiangxi, PR China 2 School of Resource, Environmental and Chemical Engineering, Nanchang University, Nanchang 330031, Jiangxi, PR China 3 School for Engineering of Matter, Transport and Energy, Arizona State University, 551 E. Tyler Mall, Tempe, AZ 85287, USA

*Corresponding author:

1. Dr. Shuguang Deng, Tel.: +8613813996873,E-mail: [email protected] (S. Deng) 2. Dr. Jun Wang, E-mail:[email protected] (J. Wang)

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Abstract: It is very challenging to achieve efficient and deep desulfurization, especially, in flue gases with an extremely low SO2 concentration. Herein, we report a microporous metal– organic framework (ELM-12) with specific polar sites and proper pore size for the highly efficient SO2 removal from flue gas and other SO2-containing gases. A high SO2 capacity of 61.2 cm3 g-1 combined with exceptionally outstanding selectivity of SO2/CO2 (30), SO2/CH4 (871), and SO2/N2 (4064) under ambient conditions (i.e., 10:90 mixture at 298 K and 1 bar) was achieved. Notably, the SO2/N2 selectivity is unprecedented among ever reported values of porous materials. Moreover, the DFT-D calculations illustrated the superior SO2 capture ability and selectivity arise from the high density SO2 binding sites of CF3SO3- group in the pore cavity (S

δ+···O δ−

interactions) and aromatic linkers in the pore walls (H

δ+···O δ−

interactions).

Dynamic breakthrough experiments confirm the regeneration stability and excellent separation performance. Furthermore, ELM-12 is also stable after exposure to SO2, water vapor, and organic solvents. Keywords: Desulfurization, SO2 capture, Polar sites, IAST selectivity, Reversible

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1. Introduction Excessive energy is consumed by the ever-growing population and economy, which includes the massive utilization of low-grade coal and fuels.1,2 Sulfur dioxide (SO2) emissions induced by the combustion of these fossil fuels are serious threat to human health and detriment on environment.3,4 Besides, SO2 emissions are noxious to many industrial operations. For example, trace SO2 could irreversibly deactivate the catalysts in the selective catalytic NOx reduction and catalytic CH4 combustion.5,6 Moreover, a low concentration of SO2 (cat. 2000 ppm) will significantly degrade the performance of the adsorbents or absorbents in the process of removing CO2 from flue gases.7,8 To address this issue, various flue gas desulfurization (FGD) techniques have been deployed for industrial applications. Up to date, ammonia scrubbing and limestone scrubbing techniques are the mainstream FGD techniques, which can remove about 90-95% SO2 from gas-mixtures.9 However, the traditional FGD processes are energy-intensive and produce a large amount of low-grade byproducts, failing the efficient principles for the deep desulfurization. Therefore, it is urgent to develop an efficient technology to selectively remove SO2 from flue gas and other SO2 containing gases. In the past decades, physisorption employing advanced porous materials as adsorbents has been regarded as a promising method to separate impurities and pollutants from gas-mixtures owing to its low-energy penalty, outstanding separation performance, and mild operation conditions.10,11 Whereas, considering the highly corrosive and reactive nature of SO2 and the extremely low SO2 concentration in the flue-gas (the typical composition of flue gas: N2 = 7075%; CO2 =10-15%; SO2 = 500-3000 ppm),7,12 it is still very challenging to prepare an excellent absorbent with high SO2/N2 and SO2/CO2 selectivity and with considerable stability. 3



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Metal-organic frameworks (MOFs) have attracted great attentions due to their tunable porous structure and designable surface chemistry,13,14 thus, they are prominent in various industrial applications, such as gas storage/separation,15,16 catalyst,17,18 and electrode materials.19 By adjusting the organic linkers and metal clusters, the pore aperture size and surface polarity could be precisely amended to promise potential for gas separation and capture.20-22 Numerous investigation have focused on screening MOFs to separate CO2 and hydrocarbons.23-25 Whereas, the SO2 adsorption and separation on MOFs are rarely reported and investigated, especially at ultra-low partial pressures that is practically required by the deep gas desulfurization.26,27 Until very recent, novel MOFs showed superior selective SO2 adsorption performance by optimizing the interactions between the MOF hosts and the adsorbate molecules are illustrated. For example, Xing et al.28 reported a series of inorganic anion (SiF62−, SIFSIX) pillared MOFs for the selective recognition and dense packing of SO2 clusters through multiple supramolecular recognition sites with SO2 molecules via Sδ+···Fδ− electrostatic interactions. Savage et al.29 illustrated that the specific multiple supramolecular interactions would be generated by the adsorbed SO2 molecules with free hydroxyl groups and aromatic rings on the pore surface of ultra-robust MOF material MFM-300(In). Mon et al.30 demonstrated that introducing basic defects of missing-linker and extra barium cations could enhance the SO2 adsorption capacity. The above exciting progresses prompted us to explore efficient adsorbents for low concentration SO2 separation and removal. Herein, we report a highly selective SO2 adsorption and separation on a microporous metal–organic

framework,

[Cu(bpy)2(OTf)2]

(bpy

=

4,4’-bipyridine,

OTf

-

=

trifuoromethanesulfonate, also called ELM-12) with polar CF3SO3- groups, and the specific 4


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recognition sites enable the highly efficient SO2 removal from gas mixtures. It showed acceptable SO2 uptake of 61.2 cm3 g-1 combined with outstanding selectivity of SO2/CO2 (30), SO2/CH4 (871), and unprecedented SO2/N2 selectivity of 4064 under ambient conditions (i.e., 10:90 mixture at 298 K and 1 bar). The pore size window of ELM-12 (4.3Å × 4.3Å × 6.1 Å) is suitable for the kinetic size of SO2 (4.1 Å), promoting the acceptable SO2 adsorption capacity and outstanding selectivity. Furthermore, the SO2 binding sites were clearly illustrated by DFT simulation studies, including high density binding sites of CF3SO3- group in the pore cavity (S δ+···O δ−

interactions) and aromatic linkers in the pore walls (H

δ+···O δ−

interactions). The

excellent SO2 separation performance and recycle stability were further elucidated by breakthrough experiments with a practical flue gas composition. It is worth noting that no noticeable framework degradation was observed on the ELM-12 samples after they were exposed to SO2, water vapor, and organic solvents.

2. Experimental section 2.1 Materials All reagents were commercially available and used as received without further purification. Copper(II) trifluoromethanesulfonate [Cu(OTf)2] was purchased from EnergyChemical Co., Ltd. 4,4'-Bipyridine (bpy) was purchased from Xilong Scientific Co., Ltd. Methanol and acetone was purchased from Aladdin reagent co., Ltd.

2.2 Synthesis of [Cu(bpy)2(OTf)2] (ELM-12) [Cu(bpy)2(OTf)2] (ELM-12) was synthesized according to the literature with some modifications.31,32 Typically, a solution of bpy (2.0 mmol, 0.312 g) in 10 mL acetone was carefully layered onto 17.5 mL Methanol/H2O (1:7 v/v) solution containing Cu(OTf)2 (1.0 5



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mmol, 0.362 g) without stirring at room temperature. Then, the mixture was placed for 3 days in still to obtain [Cu(bpy)2(OTf)2]. The crystals were filtered, washed with methanol for several times and dried in vacuum at 60 °C for 12 h.

2.3 Material Characterization The crystallinities and phase purities of obtained samples were measured by powder Xray diffraction (PXRD) analysis on a PANalytical empyrean series2 diffractometer with CuKa radiation with a step size of 0.0167o, a scan time of 15s per step, and 2θ ranging from 5 to 90o, at room temperature. Scanning electron microscopy (SEM) images were recorded in a JSM 6701F instrument.

2.4 Adsorption Measurements As shown in Scheme S1, a dual-chamber volumetric adsorption apparatus was built for measuring SO2 adsorption following a previously reported unit in the literature.33,34 The single component adsorption isotherms of CO2, CH4 and N2 at 273 K and 298 K were measured in a Micromeritics ASAP 2460 adsorption apparatus (Micromeritic Instruments, USA). The degassing procedure was repeated on all samples at 393 K and vacuum for 12 h before each adsorption measurements. The specific BET (Brunauer−Emmett−Teller) surface area was calculated based on the N2 adsorption isotherm data (0.05 and 0.3 relative pressure) at 77 K. The breakthrough experiment setup was shown in Figure S4. The separation performance for binary mixtures in ELM-12 can be simplified and compared in terms of adsorption selectivity, S, defined for binary mixtures as S 

q1 q2 , were calculated according to ideal p1 p2

adsorption solution theory (IAST) model proposed by Myers et al, 35,36 where, q1 and q2 are the 6


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absolute component loadings (mol kg-1) of the adsorbed phase in the binary mixture at partial pressures P1 and P2 (Pa).

2.5 Density Functional Theory Calculation Methods. First-principles density functional theory (DFT) calculations were conducted using the Quantum-Espresso package.37 We introduced a semiempirical addition of dispersive forces to conventional DFT calculation method to include van der Waals interactions.38 The Vanderbilttype ultrasoft pseudopotentials and generalized gradient approximation (GGA) with a Perdew−Burke−Ernzerhof (PBE) exchange correlation were also taken into account as well. The Monkhosrt-Pack scheme was applied to generate a cutoff energy of 544 eV and a 2 × 2 × 2 k-point mesh to cover the total energy within 0.01 meV/atom. After the optimization the open-pore structure of ELM-12, adsorbate molecules were introduced into various locations of the pore structures, then followed by a full structural relaxation. In order to calculate the gas binding energy, the reference of an isolated gas molecule that placed in an identical supercell of ELM-12 was also fully relaxed. The static binding energy (at T = 0 K) was calculated using EB = E(MOF) + E(SO2) − E(MOF + SO2).

3. Results and discussion 3.1 Characterization of ELM-12 Using

the

commercially

available

raw

organic

ligands

of

Copper(II)

trifluoromethanesulfonate and 4,4'-bipyridine, the ELM-12 could be prepared under mild conditions with a slight modification of previously reported procedure.39,31 Each Cu(II) atom is coordinated by four bpy groups (with four N atoms) in equatorial position and two polar CF3SO3- group in axial position, which is expanded to four adjacent Cu(II) atoms through four7



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connected bpy ligands, affording 2D square-grid sheets. The 2D layers stack with a weak interlayer interaction formed between oxygen atoms of CF3SO3- group and hydrogen atoms of bpy ligands (Figure. 1a). Blue cubic single crystals could be clearly observed in the optical photographs and SEM images (Figure. 1b), indicating that the ELM-12 are well crystallized. The PXRD patterns, showed the characteristic peaks of ELM-12 (Figure. 1c), are in consistent with the simulated pattern, confirming the successfully synthesis of ELM-12 with high purity, and the intact framework structure could be maintained upon activation. The TGA curve, in Figure. S2b, showed that ELM-12 is thermally stable up to 320 °C in a N2 flow that could deal with the practical FGD scenario. Figure. S2a shows the N2 adsorption-desorption isotherms at 77 K, the adsorption isotherms show a steep uptake at relative low-pressure region and followed by a sharp knee and plateau, the obvious stepwise N2 adsorption on ELM-12 derives from the micropore filling and a subsequent gate-opening effect. Notably, there is a clear disagreement in the adsorption and desorption branch, which stems from a diffusion restriction caused by the narrow pores.31,32 The specific Brunauer-Emmett-Teller (BET) surface area of activated ELM-12 was measured to be 706 m2 g-1 with a total pore volume of 0.26 cm3 g-1 (Figure. S2a). Besides, ELM-12 possesses 2D zigzag channels with a pore window of 4.3Å × 4.3Å × 6.1 Å,40 which match well with the size of SO2 (4.1 Å), suggesting a potent potential for SO2 adsorption and separation.

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Figure 1. (a) Illustration of the crystal structure of ELM-12. Hydrogen atoms are omitted for clarity (Cu, light blue; O, red; F, green; S, yellow; N, blue; C, gray). (b) SEM images and photograph of crystal sample. (c) Powder X-ray diffraction (PXRD) patterns of ELM-12 sample.

3.2 Adsorption and separation performance of ELM-12 Single-component adsorption isotherms of SO2 on ELM-12 were measured at 273 and 298 K (Figures. 2a and S3a). The saturation adsorption capacity on ELM-12 reached 67.2 and 61.2 cm3 g-1 at 273 and 298 K under 1 bar, respectively. These values outperform many other porous materials (Figure. 2b), such as FMOF-2 (49 cm3 g-1),41 SIFSIX-3-Zn (44.8 cm3 g-1),28 9



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Prussian blue analogues ZnCo (41.1 cm3 g-1),42 mesoporous carbon (4.8 cm3 g-1),43 and even comparable to MFI zeolite (63.1 cm3 g-1)44 and PCP (67.9 cm3 g-1).45 It is worthy to note that the SO2 adsorption isotherm exhibits a steep increase in low-pressure range and reached 48.4 and 43.7 cm3 g-1 at 0.1 bar and 273 and 298 K, respectively, which accounts for ~72% of the total uptake at 1.0 bar and 298 K. It strongly indicates the potent application potential in FGD applications. By the virtue of polar nature of CF3SO3- groups in ELM-12 framework, highly selective SO2 capture capability in gas desulfurization processes is expected. The single component adsorption isotherms of CO2, CH4, and N2 on ELM-12 materials were measured at 273 K and 298 K under 1 bar (Figures. 2a and S3a). The CO2 isotherms exhibited much lower adsorption capacity than that of SO2, despite CO2 has a smaller kinetic diameter (3.30 Å) and the similar acidic nature. The highest CO2 capacity measured to be 49.9 and 29.3 cm3 g-1 at 273 and 298 K under 1 bar, respectively. This results indicate that the interactions between ELM-12 frameworks and SO2 molecules are much stronger than that of CO2 molecules, it is likely attributed to the higher dipole moment of SO2 (1.62 D) than that of CO2 (0 D) and higher polarizability of SO2 (47.7 × 10-25 cm3) than that of CO2 (26.5 × 10-25 cm3).46-48 However, ELM-12 only displayed 9.7 cm3 g-1 and 1.2 cm3 g-1 capacities of CH4 and N2 at 298 K and 1 bar, respectively, which are negligible compared with the SO2 uptake capacity. Especially at low pressures (Figure 2a insert), the SO2 uptake increases sharply and is much higher than that of other components in the flue gases. This phenomenon is caused by the relatively low dipole moments and polarizability for CH4 (0 D and 26.0×10-25 cm3) and N2 (0 D and 17.6×10-25 cm3) as well as their nonacid-base properties.48 10


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To predict the separation selectivity in gas desulfurization processes on ELM-12, ideal adsorbed solution theory (IAST) calculations were performed on SO2/CO2, SO2/CH4 and SO2/N2 mixtures. As expected, outstanding SO2/CO2 selectivity is calculated to be 30 for SO2/CO2 (10/90, v/v) mixture at 298 K and 1 bar, which is comparable to MFM-601 (32).49 It is worthy to note that the flexible ELM-12 showed a S-shaped CO2 adsorption isotherms with a smaller adsorption capacity at low pressure range,50 implying a higher SO2/CO2 selectivity in actual desulfurization process of flue gas. An outstanding SO2/CH4 selectivity of 871 was obtained for SO2/CH4 (10/90, v/v) mixture at 298 K and 1 bar, this value is almost 3 times higher than that of MFM-300(In) (275).29 Impressively, an unprecedent SO2/N2 selectivity of 7305 and 4068 at 273 and 298 K under 1 bar, respectively is obtained in a SO2/N2 (10/90, v/v) mixture, which could be ascribed to the high density of strong polarity of CF3SO3- group in ELM-12 pore channels. To our best acknowledge, it is the highest value ever reported in porous materials and much higher than that of MFM-601 (255),49 SIFSIX-1-Cu (3146),28 and MFM300(In) (2700)29, as shown in Figure 2d and Table 1.

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Figure 2. (a) SO2, CO2, CH4 and N2 sorption isotherms for ELM-12 at 298 K. (b) Adsorption isotherms of SO2 in varies materials at 298 K. (c) The IAST selectivities of SO2/CO2 (10/90), SO2/CH4 (10/90), and SO2/N2 (10/90) mixtures at 298K. (d) SO2/N2 mixtures with varying SO2 molar fractions in gas phase at 100 kPa.

Table 1. Comparison of separation properties of ELM-12 with other adsorbents at 298K and 1 bar.

Sample

SBET (m2 g-1)

SO2 (cm3 g-1) 0.1bar

1bar

SO2/CO2 (10:90)

SO2/CH4 (10:90)

SO2/N2 (10:90)

Qst kJ mol-1

Ref.

ELM-12

706

43.7

61.2

30

871

4064

41.6

This Work

FMOF-2

378

10.8

43.7

-

-

-

-

41

MIF-zeolite

713

9.4

63.1

-

-

-

-

51

Prussian blue analogues ZnCo

700

13.3

41.1

-

-

-

-

42

MFM-300(In)

1071

161.3

185.5

50

275

2700

39.6

29

MFM-601

3644

112

275.5

32

/

255

38

49 12


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SIFSIX-1-Cu

1178

195.8

246.4

71

1241

3146

36.1

28

SIFSIX-3-Zn

250

42.3

47.0

-

276

507

45.2

28

3.3 Simulation Studies To gain an explicit relationship between the framework properties of ELM-12 and adsorbate molecules, the first-principles dispersion-corrected density functional theory (DFT-D) calculations were conducted. Figure. 3a shows the optimized structure of SO2 adsorption in ELM-12 pore channels, and reveals that the small window size of 4.3Å × 4.3Å × 6.1 Å could accommodate two SO2 molecules in each pore cavity with two binding sites. Figure. 3b reveals that SO2 molecules were primarily adsorbed through the S

δ+···O δ−

electrostatic interaction

with CF3SO3- group as the first binding site with a S···O distance of 2.63-2.66 Å. Noticeably, it is shorter than the sum of van der Waals radii of O (1.52 Å) and S (1.20 Å) atoms, revealing an extremely strong interaction that arises from the electronegative nature of CF3SO3- group and positive charge of S atom in SO2 molecule. The second binding sites are presented in Figure 3c, the multiple O δ−···H δ+ dipole-dipole interactions between O atoms of SO2 molecules and aromatic hydrogens of bpy linkers with O

δ−···H δ+

distance of 2.37-3.07 Å. Thus, two SO2

molecules could be firmly trapped per unit cell via the host–guest S δ+···O δ− and O δ−···H δ+ interactions. In contrast, CO2 molecules only showed single binding site via C···O interactions between the C atoms of CO2 molecules and O atoms of CF3SO3- groups with distance of 2.95-3.09 Å (Figure 3d). The DFT-D calculated static binding energy of CO2 molecules on ELM-12 is 32.5 kJ mol-1, which is much lower than that of SO2 molecules (51.7 kJ mol-1). The experimental adsorption enthalpy (Qst) of SO2 on ELM-12 is calculated to be 41.6 kJ mol-1 by 13



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Clausius−Clapeyron equation (Figure 4d),15,52 which is higher than that of MFM-300(In) (39.6 kJ mol-1),29 MFM-601 (38 kJ mol-1)49 and SIFSIX-1-Cu (36.1 kJ mol-1).28 This high adsorption enthalpy (Qst) confirms its strong interaction between ELM-12 and SO2 molecules. The static SO2 binding energy is slightly higher than the calculated Qst value, which is caused by the difference definitions and the limitation of the DFT-D approach.

Figure 3. DFT-calculated (a) SO2 adsorption in pore channels, (b) SO2 adsorption through the S δ+···O δ−, (c) SO2 adsorption through the O δ−···Hδ+ interactions, (d) CO2 adsorption through the C···O interactions. locations in ELM-12. Color code: O, red; S, yellow; C, gray; F, green.

3.4 Dynamic Breakthrough Performance To evaluate the feasibility of ELM-12 for the separation of SO2/CO2 and SO2/N2, real-time dynamic breakthrough experiments were carried out with a gas-mixture of 2000 ppm SO2 in 14


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CO2 and N2 balances with a flow rate of 20 mL min-1 at 298 K. As shown in Figure 4a, CO2 rapidly eluted within 16 minutes and followed by SO2 in 400 minutes, highly efficient elimination of SO2 was achieved. Besides, the dynamic SO2 uptake capacity was calculated to be 0.90 mmol g-1 from SO2/CO2 gas mixture. For SO2/N2 mixtures (Figure 4b), efficient and clean separations were achieved with a breakthrough time interval of 800 minutes, suggesting that ELM-12 is quite efficient for practical desulfurization applications. In order to further demonstrate the outstanding separation performance, dynamic breakthrough experiments with actual flue gas compositions were conducted. As show in Figure 4c，ELM-12 retained the excellent separation ability even with the co-existence of N2, O2 and CO2.

Figure 4. Cycling column breakthrough curve for (a) CO2/SO2 (2000 ppm SO2) mixture, (b) N2/SO2 (2000 ppm SO2) mixture, (c) actual flue gas compositions, (d) Isosteric heat of SO2 adsorption. 15



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Stable cycling performance and easy regeneration of adsorbents are essential parameters to realize cost-effective and low-energy penalty applications. We perform multiple dynamic breakthrough tests with SO2/N2 (0.2/99.8), SO2/CO2 (0.2/99.8), and actual flue gas gasmixtures to verify the stable separation ability of ELM-12. As shown in Figures. 4a and 4b, there is no obvious performance decay observed on SO2 capacity and breakthrough time during 5 cycles. The PXRD patterns also indicated that ELM-12 could retain the intact framework after breakthrough cycles (Figure. 5a). The adsorbent could be fully regenerated by He flow at 313 K (Figure S5b). In addition, the temperature of directly emitted flue gas streams is about 353 K, thus the thermal stability is another key factor for practical adsorption applications.53 As shown in Figure. 5a, the crystal structure of ELM-12 retain intact after the sample were heated at 393, 423, and 473 K for 24 hours. Furthermore, the SO2 adsorption isotherms on the heat-treated ELM-12 were recorded in Figure. 5b. Even at such harsh conditions, the undiminished adsorption capacity was achieved on ELM-12. The solvent stability of ELM-12 was further examined, the ELM-12 was soaked in water and five common organic solvents for 24 hours and the intact PXRD patterns also reveals the strong resistance of water and organic solvents. Because SO2 gases are highly corrosive, the stability of ELM-12 in SO2 atmosphere should be examined. Notably, the framework skeleton of ELM-12 remains intact after exposure to pure SO2 for 8 hours, whereas the framework of ZIF-67 is completely destroyed (Figure. 5d).

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Figure 5. Stability test for ELM-12. Powder X-ray diffraction patterns of (a) after heat treatment, (b) SO2 adsorption after thermal treatments and breakthrough cycles, (c) after solvent treatment, and (d) after exposure to SO2 atmosphere for 8 h.

4. Conclusion In summary, a highly selective and stable SO2 adsorption on a microporous metal–organic framework (ELM-12) with special polar CF3SO3- group and proper micropore size was achieved. The highest IAST selectivity of SO2/CO2, SO2/CH4, and SO2/N2 was up to 30, 871 and 4064 under ambient conditions (i.e., 10:90 mixture at 298 K and 1 bar), respectively. Notably, the selectivity of SO2/N2 is the highest so far. Furthermore, it is clearly demonstrated that the acceptable SO2 capture ability and selectivity was ascribed to multiple binding sites of anionic (Sδ+···Oδ− interactions) and aromatic linkers (Hδ+···Oδ− interactions) through DFT-D 17



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calculations. The separation performance for SO2 mixtures on ELM-12 has been clearly demonstrated by the breakthrough experiments with SO2/N2 (0.2/99.8), SO2/CO2 (0.2/99.8), and actual flue gas mixtures. The structure stability is also illustrated, no noticeable framework degradation was observed after exposure to SO2, water vapor, and organic solvents. Highly efficient separation performances combined with stable structure make ELM-12 as a potent material for practical desulfurization processes. Supporting Information SEM and single crystal images, N2 adsorption-desorption curves at 77 K, TGA curves, SO2 adsorption isotherm at 313 K, and desorption SO2 curves of ELM-12; SO2 adsorption and gasmixture breakthrough measurements details; isotherms fitting and IAST calculation details, table of Single-site Langmuir-Freundlich fitting parameters. Acknowledgement The research work was supported by National Natural Science Foundation of China (No. 51672186). Authors would like to acknowledge the start-up fund from Nanchang University and Arizona State University. We show great gratitude to Prof. Shuhua Zhang’s group at Guilin University of Technology for the DFT-D simulation.

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Highly Selective and Reversible Sulfur Dioxide Adsorption on a

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