Methane Storage in Metal Organic Frameworks: Current Records, Surprise Findings, and Challenges

Transcription

1 Methane Storage in Metal rganic Frameworks: Current Records, Surprise Findings, and Challenges Yang Peng,, Vaiva Krungleviciute,, Ibrahim Eryazici, Joseph T. Hupp, mar K. Farha,,* and Taner Yildirim,,,* Institutions: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania Department of Chemistry and International Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 628 * Corresponding authors: taner@seas.upenn.edu and o-farha@northwestern.edu Table of Contents Section S1. Synthesis of MFs S2-8 Section S2. Nitrogen Isotherms S9-S11 Section S3. Volumetric High-Pressure Adsorption Measurements S12-S14 Section S4. Total and Excess Methane Isotherms S15-S22 Section S5. Isosteric Heat of Adsorption Q st S22-S25 Section S6. Pellets from compressed HKUST-1; pore volume and x-ray diffraction S26 Section S7. References S26 Note: Here we have identified certain commercial suppliers to foster understanding and accurate comparisons to other reported work. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. S1

2 Section S1. Synthesis of MFs MF sample were freshly prepared using methods reported in the literature (see below for details). All other samples were synthesized easily in several 1 mg quantities. For HKUST-1, PCN-14, and NU- 125, we have also repeated the room temperature isotherm measurements using one-gram samples. All samples were thoroughly outgassed to remove residue solvent; sample handling was done in a heliumfilled glove box. The samples were activated immediately before sorption measurements. Gas sorption measurements were performed on a carefully calibrated, high accuracy, Sieverts apparatus under computer control. Instrument and measurement-protocol details have been published elsewhere 7 ; more details are given below. All gases were of Research or Scientific grade, with a minimum purity of %. Below we give brief description of the synthesis of the four MFs studied in this work. We have recently described the synthesis of NU-125 and NU-111 in Ref.1 and Ref.2, respectively and therefore do not repeat them here. General procedures, materials, and instrumentations. All air- or water-sensitive reactions were carried out under a dry nitrogen atmosphere using standard Schlenk techniques. Unless otherwise stated, all chemicals and solvents were purchased from Aldrich Chemicals Co. (Milwaukee, WI) and used without further purification. Deuterated solvents were purchased from Cambridge Isotope Laboratories (Andover, MA) and used without further purification. All dry solvents were collected under inert gases, degassed under vacuum, and stored under nitrogen in a Strauss flask prior to use. 1 H and 13 C NMR spectra were recorded on a Bruker 5 FT-NMR spectrometer ( MHz for 1 H, MHz for 13 C). 1 H NMR data are reported as follows: chemical shift (multiplicity (b = broad singlet, s = singlet, d = doublet, t = triplet, q = quartet,), integration, and peak assignments, coupling constants). 1 H and 13 C chemical shifts are reported in ppm with the residual solvent resonances as internal standards. Microwave experiments were performed in a Biotage (Uppsala, Sweden) SPX microwave reactor (software version 2.3, build 625). Desired temperature was entered in the software and the reactor tuned the microwave power to obtain desired temperature and kept it stable in course of the reaction depending on the headspace available in the vial. All reactions were magnetically stirred during irradiation using the built-in magnetic stirrer. Synthesis of PCN-14 Ligand H 4 adip, 5,5 -(9,1-Anthracenediyl)di-isophthalic Acid: We have synthesized PCN-14 ligand from two different methods. Below we describe both methods. Simplified Method (developed at NIST): H 3 C H 3 C B B CH Br CH 3 CH 3 CH 3 Ph(PPh 3 ) 4 degassed Dioxane K 2 C 3 Solid Reflux under N 2 for 4 h Synthesis of 5,5 -(9,1-Anthracenediyl)bis(1,3-benzenedimethoxycarbonyl), A. Anthracene 9,1-diboronic acid bis(pinacol) (1.26 g, 2.93mmol), dimethyl-5-bromo-isophtalate (2.37 g, 8.88 mmol), Pd(PPh 3 ) 4 (4 mg) and K 2 C 3 (6.1 g 44.4 mmol) were mixed in a 5 ml three neck round bottle in a glove box. The flask was taken out of the glove box and purged with N 2 for 1 min. Then, a 15 ml of degassed 1.4-dioxane was added under N 2. The pink slurry mixture was H 3 C H 3 C CH 3 CH 3 S2

3 heated to reflux under nitrogen atmosphere for 4 h. The resulting light yellow mixture was quickly filtered while it was still hot. The filtrate was cooled at room temperature for a couple of hours and the yellow precipitate was collected. It was dried under the vacuum. (.996 g, 59%). Synthesis of H 4 adip, 5,5 -(9,1-Anthracenediyl)di-isophthalic Acid, B. Compound A (.996 g, 1.66 mmol) was suspended in 83 ml of THF, to which 17 ml of a 2 M KH aqueous solution was added (2 g KH dissolves in 17 ml H 2 ). The mixture was stirred at room temperature overnight. The solution became clear with a bilayer solution (THF is on the top and H 2 is on the bottom). THF was removed via a rotary evaporator. The solution was then diluted with hydrochloric acid (2M) until it became acidic (PH 1-2). The yellow solid was collected by filtration, washed with water then methanol and dried under vacuum to give B (.83 g, 1%). riginal Method (developed at NU): Scheme S1. The synthesis of tetraacid 6 (LH 4 ) ligand used in the preparation of PCN-14 MF. Synthesis of 9,1-diiodoantracene (2). This compound was synthesized following a modified literature procedure 3. 9,1-Dibromoantracene (1, 4. g, 11.9 mmol) was dissolved in anhydrous diethyl ether (1 ml) in a 25 ml Schlenk flask equipped with a magnetic stir bar under N 2 atmosphere. Then n-buli (12. ml of a 2.6 M solution in hexane, 31.2 mmol) was added slowly to this solution over the course of 3 minutes at C. The reaction mixture was stirred 2 minutes after completion of the addition, and then brought up to room temperature. Iodine (1 g, 39.4 mmole) was added to this mixture, which was stirred for 3 more minutes (until the reaction mixture turned to dark brown color). The final reaction mixture was then extracted with aqueous Na 2 S 2 3 solution (25% w/w, 5 1 ml) and ether layer was collected, concentrated and dried. Remaining solid was recrystallized two times in CCl 4 (2 12 ml) to give the product 2 as yellow needle-like crystals, which was dried under high vacuum. Isolated yield = 2.2 g (43%). 1 H NMR (THF-d 8 ): 7.64 (q, 4 H, 1,4,5,8-Antracene-H, J = 2.1 Hz) and 8.57 (q, 4 H, 2,3,6,7-Antracene-H, J = 2.1 Hz). 13 C NMR (THF-d 8 ): δ 19.1, 129.1, 135.2, and S3

4 Synthesis of 3,5-bis(methoxycarbonyl)phenylboronic acid pinacol ester (4). This compound was synthesized following a modified literature procedure 4. Pd(dppf) 2 Cl 2.CH 2 Cl 2 (3.7 g, 4.48 mmol) and KAc (26 g, 265 mmol) were added to a stirring solution containing compound 3 (25 g, 91.5mmol), bis(pinacolato)diboron (28 g, 11 mmol), and dioxane (15 ml) in 5 ml Schlenk flask equipped with a magnetic stir bar and a rubber stopper. The resulting solution was cooled down to -78 C in acetone/dry ice bath and subjected to three cycles of brief vacuum-degas/n 2 back-fill with no stirring. The flask was then fitted to a water-cooled condenser and refluxed for 15 h under N 2. Then the reaction mixture was allowed to cool to room temperature and EtAc (3 ml) was added to the resulting mixture, which was then filtered. The filtrate was collected, concentrated, and dried under high vacuum. Remaining semisolid was dissolved in CH 2 Cl 2 and column chromatographed using silica gel and CH 2 Cl 2. The first eluting spot was collected, concentrated, and dried under high vacuum affording a white solid, which was suspended in hexanes (2 ml) and sonicated for 3 minutes. This mixture was then filtered to give the product 4 (17.5 g) as a white solid, which was dried under high vacuum. The filtrate was then kept at - 1 C overnight and filtered to afford more product 4 (6.5 g) as a white solid, which was dried under high vacuum. Isolated yield = 24 g (81%). 1 H NMR (CDCl 3 ): δ 1.35 (s, 12 H, B-(-C(CH 3 ) 2 ) 2, 3.93 (s, 6 H, C 2 CH 3 ), 8.62 (d, 2 H, 2,4-Benzene-H, J = 1.5 Hz), and 8.75 (t, 1 H, 5-Benzene-H, J = 1.5 Hz). 13 C NMR (CDCl 3 ): δ 25., 52.4, 84.5, 13.2, 133.4, 14., and Synthesis of 5,5 -(9,1-Anthracenediyl)bis(1,3-benzenedimethoxycarbonyl) (5) 5. Compound 2 (3 mg,.7 mmole), compound 4 (886 mg, 2.8 mmole), Pd(PPh 3 ) 4 (86.4 mg,.75 mmole), K 2 C 3 (443 mg, 3.2 mmole), and degassed and anhydrous 1,4-dioxane (15 ml) were added to a 2 ml microwave reactor vial in a dry box and sealed, then this mixture was microwave-irradiated at 15 ºC for 5 hours. The aforementioned reaction procedure was repeated ten times and all ten reaction mixtures were combined and vials were washed with CHCl 3, which was added into the dioxane solution. This mixture was sonicated for 3 minutes and then filtered. The filtrate was collected, concentrated and dried under high vacuum affording dark brown paste, which was sonicated in hexanes (1 L) for 3 minutes and filtered again. The solid was collected and dissolved in CHCl 3 (5 ml) and filtered. The filtrate was collected, concentrated and column chromatographed over silica gel using CHCl 3 (contains 2% EtH as a stabilizer) to give 5 as a white solid, which was dried under high vacuum. Isolated yield = 2.7 g (68%). 1 H NMR (CDCl 3 ): δ 3.98 (s, 12 H, C 2 CH 3 ), 7.37 (q, 4 H, 2,3,6,7-Antracene-H, J = 2.1 Hz), 7.56 (q, 4 H, 1,4,5,8-Antracene-H, J = 2.1 Hz), 8.37 (d, 4 H, 2,4-Benzene-H, J = 1.5 Hz), and 8.92 (t, 2 H, 5- Benzene-H, J = 1.5 Hz). Synthesis of 5,5 -(9,1-Anthracenediyl)di-isophthalicAcid (6, LH 4 ) 5. Compound 5 (2.6 g, 4.6 mmol) was dissolved in 1,4-dioxane (175 ml) in a 1 L round bottom flask equipped with a magnetic stir bar. Then, KH (23 ml, 1 M aqueous solution, 23 mmol) was added to this solution affording a suspension, which was refluxed for 18 h until the suspension become a clear solution. Dioxane was removed using a rotary evaporator and the remaining aqueous solution was acidified to ph 2 using concentrated HCl (2 ml of a 37% aqueous solution). The resulting precipitate was collected via centrifugation (65 rpm), washed with H 2 (2 ml) and acetone (1 ml), and dried under high vacuum to afford 6 (LH 4 ) as a light yellow solid. Isolated yield = 2.3 g (99%). 1 H NMR (DMS-d 6 ): δ 7.49 (q, 4 H, 2,3,6,7-Antracene-H, J = 2.1 Hz), 7.55 (q, 4 H, 1,4,5,8-Antracene-H, J = 2.1 Hz), 8.2 (d, 4 H, 2,4-Benzene-H, J = 1.5 Hz), 8.72 (t, 2 H, 5-Benzene-H, J = 1.5 Hz), and (s, broad, 4 H, C 2 H). 13 C NMR (DMS-d 6 ): δ 126.2, 126.3, 129.2, 129.6, 132., 135.1, 135.6, 138.9, and S4

5 Figure S1. 1 H NMR spectra of 2 recorded in THF-d 8. Figure S2. 13 C NMR spectra of 2 in THF-d 8. S5

6 Figure S3. 1 H NMR spectra of 4 recorded in CDCl 3. Figure S4. 13 C NMR spectra of 4 in CDCl 3. S6

7 Figure S5. 1 H NMR spectra of 5 recorded in CDCl 3. Figure S6. 1 H NMR spectra of 6 recorded in DMS-d 6. S7

8 Figure S7. 13 C NMR spectra of 6 recorded in DMS-d 6. Synthesis of HKUST-1. Cu(N 3 ) 2 3H 2 (5. g, 21.4 mmole) was dissolved in 6 ml of H 2. In a separate flask, BTC (1.36 g, 6.4 mmole) (BTC = 1,3,5-benzenetricarboxylate) was dissolved in 6 ml of EtH. The Cu(N 3 ) 2 3H 2 solution was slowly added to the BTC solution with stirring at room temperature. DMF (4 ml) was added to the slurry and the combination was transferred to a 18 ml Teflon-lined autoclave and cooked at 8 C for 2 h. After allowing the autoclave and its contents to cool to room temperature, a blue crystalline solid was collected and washed with lots of methanol for several times. The as-synthesized sample was activated under vacuum at 12 C for 12 hrs. We scaled this recipe up and down from 1 mg to 4 gram sample and basically obtained same pore volume around.78 cc/g. Hence, the synthesis of HKUST-1 is quite easy and easily reproducible. Synthesis of UTSA-2. The solvothermal reaction of H 6 BHB (1 mg,.18 mmol) (H 6 BHB=3,3,3,5,5,5 -benzene-1,3,5-triylhexabenzoic acid) and Cu(N 3 ) 2 2.5H 2 (2 mg,.86 mmol) in N,N-dimethylformamide (DMF, 1.5 ml) with addition of two drops of HBF 4 at 65 C for 48 hours to give small green block-shaped crystals. An as-isolated sample of UTSA-2 was immersed in acetone for 24 h, and the extract was decanted. Acetone-exchanged UTSA-2 was activated at 12 C for 24 hours under vacuum. Synthesis of Ni-MF-74. A solution of nickel acetate tetrahydrate (3.73 g, mol) in 5 ml of water and a solution of 2,5-dihydroxyterephthalic acid (H 4 DBDC) (1.49 g, mol) in 5 ml of THF were combined in a 18 ml of Teflon-lined autoclave and reacted at 11 C for three days. The mother liquor was decanted and the yellow fine powder material was replaced with methanol (2 ml). The methanol was decanted and replenished two times over the four days. The solvent was removed under vacuum. Yield: 1.4g. The as-synthesized sample was activated at 25 C over 6 hours, yielding yellow-brown microcrystalline porous material. S8

9 Synthesis of PCN-14. A mixture of H 4 adip, 5,5 -(9,1-Anthracenediyl)di-isophthalic Acid (15mg), Cu(N 3 ) H 2 (6 mg), and 1.8 ml of HBF 4 in 45 ml DMF was mixed into a 6 ml screw capped jar and heated slowly to 75 C, kept at that temperature for 1 day, and were washed with DMF for twice and immersed in DMF for overnight. The as-isolated sample of PCN-14 was immersed in methanol for 24 h, and the extract was decanted. Fresh methanol was subsequently added, and the crystals were allowed to stay for an additional 24 h to remove the nonvolatile solvates (DMF). The sample was then immersed in acetone for two days and finally in CH 2 Cl 2 for 2 hours. After the removal of dichloromethane by decanting, the sample was dried in a vacuum box furnace at room temperature. (~15 mg) Activation: The sample was pumped at room temperature overnight and then it was slowly heated to 12 C and kept at this temperature for 12 hours. The activated sample mass was ~75 mg. The pore volume was measured as.85 cc/g. Note: Multiple PCN-14 samples were synthesized using linkersynthesized from two different methods by NIST and NU. The obtained samples had very similar gas adsorption properties (see Figure S24). S9

10 Section S2. Nitrogen Isotherms First, we studied the permanent porosity of activated MF samples by N 2 adsorption measurements at 77 K (Figure S1-S4). By applying the Brunauer-Emmett-Teller (BET) model in the pressure range P/P where P is determined by consistency plot, we determine the BET surface areas. The pore volume is estimated from the saturation value of the N 2 adsorption. The pore volume and surface areas are summarized in Table 1 in the main text and compared with the calculated values from PLATN. N 2 Amount Adsorbed (cc/g) v(1-p/p ) P/P Relative Pressure (P/P ) Figure S8. N 2 adsorption isotherm at 77 K for HKUST-1. The inset on the left shows the consistency plot to determine the pressure range for BET fitting 6, which is shown in the right inset. 1/[v(P /P-1)].2.1 V pore =.78 cc/g S BET = 185 m 2 /g..5.1 P/P S1

11 3 V pore =.51 cc/g N 2 Amount Adsorbed (cc/g) 2 1 v(1-p/p ) /[v(P /P-1)] S BET = 1352 m 2 /g P/P P/P Relative Pressure (P/P ) Figure S9. N 2 adsorption isotherm at 77 K for Ni-MF-74. The inset on the left shows the consistency plot to determine the pressure range for BET fitting 6, which is shown in the right inset V pore =.85 cc/g N 2 Amount Adsorbed (cc/g) v(1-p/p ) P/P P/P Relative Pressure (P/P ) Figure S1. N 2 adsorption isotherm at 77 K for PCN-14. The inset on the left shows the consistency plot to determine the pressure range for BET fitting 6, which is shown in the right inset. The black and red curve shows the nitrogen isotherms before and after all gas adsorptions are done, indicating no sign of sample degradation with gas adsorption cycles. 1/[v(P /P-1)] S BET = 22 m 2 /g S11

12 5 N 2 Amount Adsorbed (cc/g) v(1-p/p ) P/P P/P Relative Pressure (P/P ) Figure S11. N 2 adsorption isotherm at 77 K for UTSA-2. 1/[v(P /P-1)] V pore =.66 cc/g S BET = 1615 m 2 /g 15 V pore = 2.9 cc/g 8 V pore = 1.29 cc/g N 2 Amount Adsorbed (cc/g) 1 5 v(1-p/p ) /[v(P /P-1)] S BET = 493 m 2 /g N 2 Amount Adsorbed (cc/g) v(1-p/p ) 6 1/[W(P-P )-1)] S BET = 312 m 2 /g P/P P/P Relative Pressure (P/P ).1.2 P/P P/P Relative Pressure (P/P ) Figure S12. N 2 adsorption isotherm at 77 K for NU-111 (lef) and NU-125 (right). The inset on the left shows the consistency plot to determine the pressure range for BET fitting 6, which is shown in the right inset. S12

13 Section S3. Volumetric High-Pressure Adsorption Measurements and Excess Isotherms Based on the widely used volumetric method, we developed a fully computer-controlled Sieverts apparatus as discussed in detail in Ref.7. Briefly, our fully computer controlled Sievert apparatus operates in a sample temperature range of 2 K to 5 K and a pressure range of to 1 bar. In the volumetric method, gas is admitted from a dosing cell with known volume to the sample cell in a controlled manner; the gas pressure and temperature are controlled and recorded. Some unique features of our setup are as follows. We have five gas inlets including He, N 2, C 2, CH 4, and H 2, enabling us to perform first nitrogen pore volume and surface measurements and then He-cold volume determination and then the gas adsorption measurements without moving the sample from the cell and using the same protocol. We use four pressure gauges with four different pressure ranges (2, 1, 5 and 1 psi, respectively) to precisely measure the pressure (gauge accuracy ~.5%). For isotherm measurement below room temperature, the sample temperature is controlled using a closed cycle refrigerator (CCR). The difference between the real sample temperature and the control set-point is within 1 K in the whole operating temperature range. The connection between the sample cell and the dose cell is through 1/8 capillary tubing, which provides a sharp temperature interface between the sample temperature and the dose temperature (i.e., room temperature). Figure S13. A summary of the steps involved in the high-pressure isotherm measurements. The same isotherm measurements were also repeated using empty cell with 76 mg Al-foil in it, from which we determine the empty-cell cold volumes. Using both empty-cell and He-gas with sample in cold volumes we generate two isotherms. The sample after each isotherm is outgassed at 3 K for one hour for all MFs except for Ni-MF-74. Due to strong binding sites in NiMF74, the sample is outgassed at 323 K after each isotherm measurements. During the measurements, the dosing temperature was stable within +/-.5 K (i.e. ~.2% variation) and the displex cell temperature was stable within.1 K. The cold volumes for the empty cell were determined using He as a function of pressure at every temperature before the real sample measurement and were used to calculate the sample adsorption. In parallel to these empty cell based isotherms, we also measured isotherms using He gas and sample in the cell. Assuming He-adsorption is small, this method is more accurate. As shown in the Figures below, the isotherms from both methods (i.e. empty cell cold volume, and He-cold volume with the sample) agree S13

14 with each other reasonably well. As a third cross check of our measurements, we repeated all the isotherms on an empty cell with the same gas and temperatures. Using previously measured cold volumes, we verify that the empty cell does not appear to show any adsorption. Based on this empty cell absorption measurement, the error bars in our isotherms are around 1% at 35 bar and at most 2-3 % at 6 bar. Figure S6 shows the measurement protocol used in this study. In the paper (and below), we compare the absolute (and excess) isotherms obtained from He-runs (orange color) and the blank empty cell runs. For practical purposes, the two methods result in basically very similar isotherms, giving us confidence about the measurements and some idea about the error bars. The biggest difference is at 2 and 24 K where He-runs give lower isotherms. This is what we expect. At these temperatures and at high pressures, some He will be adsorbed in the sample, which results in a slightly larger cold-volume and therefore lower adsorption. Since the adsorbed amount is deducted from the raw P-V-T data using a real gas equation of state, a critically important issue is the accuracy of the chosen equation of state (ES) in terms of describing the real gas behavior within the desired temperature and pressure range. We found that the simple ES such as van der Waals (vdw) ES works well at only ambient pressure and temperature, while it cannot describe the real gas behavior at low temperature and high pressure. Alternatively, for small gas molecules, the modified Benedict-Webb-Rubin (MBWR) ES seems to work well over a wide temperature and pressure range. Using an empty cell as a reference, we found that the MBWR ES best describes the real gas behavior of He, H 2 and CH 4. Therefore, in all our isotherm data reduction, the NIST MBWR ES is used. [NIST Standard Reference Database 23: NIST Reference Fluid Thermodynamic and Transport Properties Database]. Finally, we briefly describe the calibration of the Sievert apparatus. We used pure FHC (oxygen free high conductive) copper block with known volume. The volume of the copper block were measured by an accurate-ruler and also by mass and the density of the FHC copper. Both methods give a volume within.2%, which was shown as horizontal dash-line in Figure below. We then run He-isotherms with and without the FHC-copper block in the sample cell, using pressure ranges for a given gauge (i.e. -2 psi for 2-psi gauge volume calibration, etc). The results are shown on the top panel in the Figure below. After each gauge-volume is calibrated, we run a full He-isotherm from psi to 1 psi using all the gauges (i.e. the most accurate gauge at the given pressure reading). This cross-checking of the volume is shown in the bottom panel, which gives the expected standard volume within +/-.5%. S14

15 3.15 Volume (cc) PG2 PG1 PG5 PG Volume (cc) Pressure (psi) Figure S14. The volume calibration of each pressure gauges (top) and then cross checking of the calibration by measuring the standard volume with a full He high-pressure isotherm. The agreement between the measured volume and the actual volume is very good at all pressures. The total error is within.5%, which is most probably due to errors in the volume when we assemble and disassemble the cell for empty cell and full cell measurements. S15

16 Section S4. Total and Excess Methane Isotherms Excess CH 4 Uptake (cc(stp)/cc) K 2 K 24 K 27 K 323 K HKUST Excess CH 4 Uptake (g/g) Total CH 4 Uptake (cc(stp)/cc) K 2 K 24 K 27 K 323 K HKUST Total CH 4 Uptake (g/g) Figure S15. The methane excess (left) and total (right) isotherms for HKUST-1 at various temperatures. The total (i.e. absolute) isotherms were obtained from excess isotherms by adding the amount of gas in the pore volume at the measured pressure and temperature (using the NIST MBWR real gas equation). We used the measured pore volume from the nitrogen isotherm. The orange color lines represent isotherms obtained from He-cold volume with sample in while the other isotherms are using empty-cell cold volumes. The difference is due to adsorption of He by the sample and the systematic errors in the isotherm measurements. We used 24 mg sample for this particular measurements. At 65 bar, the sample shows 2.7 mmol excess methane adsorption and at this pressure the noise level from empty-cell measurements is +/-.3 mmol. Hence we estimate ~+/- 1% error at 65 bar and. S16

17 Excess CH 4 Uptake (cc(stp)/cc) K 2 K 24 K 27 K 323 K Ni-MF Excess CH 4 Uptake (g/g) Total CH 4 Uptake (cc(stp)/cc) K 2 K 24 K 27 K 323 K Ni-MF Total CH 4 Uptake (g/g) Figure S16. Same as Fig. S15 but for Ni-MF-74. We note that unlike other MFs, the Ni-MF-74 shows significant He adsorption at high pressures below 24 K, which is expected due to high concentration of open-metal sites present in this MF. The sample mass for this particular measurement was 34 mg. At 65 bar and, the excess adsorption is 21 cc/cc which means 7.8 mmol/g. For.3 gram sample, we have 2.3 mmol adsorption. Hence the estimated error is +/- 1.3% (based on +/-.3 mmol noise level). Total CH 4 Uptake (cc(stp)/cc) K 2 K 24 K 27 K PCN Total CH 4 Uptake (g/g) Excess CH 4 Uptake (cc(stp)/cc) K 2 K 24 K 27 K PCN Excess CH 4 Uptake (g/g) Figure S17. Same as Fig. S15 but for PCN-14. We estimate the error at 65 bar as =/- ~1 %. S17

18 Excess CH 4 Uptake (cc(stp)/cc) K 2 K 24 K 27 K UTSA Excess CH 4 Uptake (g/g) Total CH 4 Uptake (cc(stp)/cc) K 2 K 24 K 27 K UTSA Total CH 4 Uptake (g/g) Figure S18. Same as Fig. S15 but for UTSA-2. CH 4 Excess Uptake (cc(stp)/cc) K 2 K 24 K 27 K NU CH 4 Excess Uptake (g/g) CH 4 Total Uptake (cc(stp)/cc) K 2 K 24 K 27 K NU CH 4 Total Uptake (g/g) Figure S19. Same as Fig. S15 but for NU-125. S18

19 5 125 K K.8 CH 4 Excess Uptake (cc(stp)/cc) K NU K 27 K CH 4 Excess Uptake (g/g) CH 4 Total Uptake (cc(stp)/cc) K 24 K 27 K NU CH 4 Total Uptake (g/g) Figure S2. Same as Fig. S15 but for NU Total CH 4 Uptake (mmol/g) 1 5 Homemade HKUST-1 (1. gram) Homemade HKUST-1 (.2 gram) Commercial HKUST-1 (.13 g) Commercial HKUST-1 (1.3 gram) 1 x Empty Cell CH 4 Adsorption Figure S21. The comparison of the total methane isotherms at room temperature with different sample masses for homemade and commercial HKUST-1 samples, respectively. pen symbols are desorption points. At the bottom we show the noise (i.e. apparent methane adsorption by empty cell) scaled by 1 which corresponds to error bar for a 1 mg sample. Using the empty-cell isotherm noise level as reference, we estimate that we have about.1% error at 65 bar for a gram sample and about 1-2% error at 65 bar for 1 mg sample. S19

20 25 Excess CH 4 Uptake (cc(stp)/cc) Homemade (1 mg, 2 ml jar, MeH wash) Homemade (1 mg, 2 ml Teflon Autoclave) Homemade (1 g, 2 ml jar, MeH washed) Commercial HKUST-1 (1.3 gram) Figure S22. The excess methane uptake from different HKUST-1 samples, prepared differently and the runs were performed at different times within six months. The reproducibility of the data from milligram to gram scale synthesized samples is within %2. The commercial HKUST-1 shows lower uptake (about 5% at 65 bar) than home-synthesized samples. Total CH 4 Uptake (cc(stp)/cc) K Sample#1 (24 mg) Sample#2 (34 mg) Figure S23. Total methane uptake isotherms from two totally different Ni-MF-74 samples at and 27 K. Measurements were taken in 3 month apart, giving confidence us about the reproducibility of the methane uptakes by different Ni-MF-74 samples. S2

21 25 CH 4 Uptake (cc(stp)/cc) Total Sample 1 (~.25 g) Sample 2 (~1 g) Sample 3 (~.25 g) Excess Figure S23. Total and excess methane uptake isotherms from three totally different PCN-14 samples at. The sample 1 and 2 were synthesized using PCN-14 linker prepared at NIST while sample 3 was synthesized using linker prepared at NU. The agreement between measurements gives us confidence about the reproducibility of the methane uptakes by different PCN-14 samples. Total CH 4 Uptake (cc(stp)/cc) HKUST-1 Ni-MF-74 PCN-14 UTSA-2 NU-125 NU-111 MFs Two site-langmuir Fit: A A 1 P/(1+A 1 P) + A 2 A 3 P/(1+A 3 P) A A 1 A 2 A 3 HKUST Ni-MF PCN UTSA NU NU Figure S25. Total methane isotherms at room temperature for all the MFs studied. The points are data and the solid lines are two site-langmuir fit. The fit parameters are shown on the right. S21

22 cc(stp)/cc Excess CH 4 Uptake g/g HKUST-1 NiMF74 PCN-14 UTSA-2 NU-125 NU Figure S26. The comparison of the volumetric and gravimetric excess methane uptake isotherms at room temperature from six MFs that we studied in this work. Section S5. Measured Isosteric Heat of Adsorption Q st In order to gain better insight into the nature of the adsorption sites and CH 4 -MF interactions, we extracted isosteric heats of adsorption (Q st ) from the temperature-dependent isotherms shown in Figure 2 of the main text using the Clausius-Clapeyron equation (see Figs. S19-S26). The results are summarized in Fig. S27. The initial values of Q st are roughly proportional to the metal content in each MF (see Table 1), suggesting that the metal center is the initial adsorption site. Ni-MF-74 shows almost constant Q st and then drops sharply near a loading of one methane molecule per Ni-site. S22

23 Q st (kj/mol) 25 2 HKUST Ni-MF-74 PCN-14 UTSA-2 NU-125 NU Amount adsorbed (cc(stp)/cc) Figure S27. Methane isosteric heat of adsorptions as a function uptake for all the MFs under study. ur isotherm data at a series of temperatures (Fig. 2 of the main text) enable us to extract the heat of adsorption Q st as a function of the adsorbed amount. Q st is calculated using the isosteric method where a series of isotherms are measured at a wide range of temperatures. These isotherms are then parameterized by cubic-spline which does not require any fitting and allows us to interpolate the isotherm at a constant loading. Then, the Q st is obtained from the ln(p) versus 1/T plots. As an alternative to cubicspline interpolation, we also obtain Q st by fitting the isotherm data using the following form of a virial equation: ln ln 1 where v, p, and T are the amount adsorbed, pressure, and temperature, respectively and a i and b i are empirical parameters. The first four constants (i.e. a, b, a1, and b1) are obtained by linearizing the isotherms (1/n versus ln p) and then we increase the number of parameters gradually (two at a time) until the improvement in the fit is not significant. Usually 1 or 12 parameters are found to be enough to obtain a good fit to the isotherms. After the isotherms are fitted, by applying Clausius-Clapeyron equation, the heat of adsorption is obtained as where R is the universal gas constant. The details can be found in [Jagiello et al, J. Chem. Eng. Data, 1995; 4; and Jagiello J at al, Langmuir 1996, 12, ]. Below we show the isotherm data (points), cubic-spline interpolation (solid lines) and the virial-fit (dotted lines) as well as the corresponding ln(p) versus 1/T plots and the Q st from both methods along with the fit parameters a i and b i for each MFs. S23

24 Total Uptake (cc(stp)/cc) Q st (kj/mol) K Ni-MF K 27 K ln(p) a i e e e e-11 b i e e e e Total Uptake (cc(stp)/cc /T Figure S28. The CH 4 adsorption isotherms (dots) for Ni-MF-74 and the virial fit (red-lines) along with the fit parameters as well as the Q st and the lnp-1/t plot. The black line in the Q st plot is obtained from the raw-data using spline method without any fitting. Total Uptake (cc(stp)/cc) Q st (kj/mol) Figure S29. Same as Fig. S28 but for HKUST K HKUST-1 24 K 27 K Total Uptake (cc(stp)/cc 323 K ln(p) 4-2 a i e e e e-14 b i e e e e e /T S24

25 Total Uptake (cc(stp)/cc) K 24 K 27 K a i e e e-11 b i e e e e-14 Q st (kj/mol) PCN-14 ln(p) Total Uptake (cc(stp)/cc /T Figure S3. Same as Fig. S28 but PCN-14. Total Uptake (cc(stp)/cc) Q st (kj/mol) Figure S31. Same as Fig. S28 but for UTSA K UTSA-2 24 K 27 K Total Uptake (cc(stp)/cc ln(p) a i e e e e-15 b i e e e e e /T S25

26 Total Uptake (cc(stp)/cc) Q st (kj/mol) Figure S32. Same as Fig. S28 but NU K NU K 27 K Total Uptake (cc(stp)/cc ln(p) a i e e e-1 b i e-5 6.5e e e /T Total Uptake (cc(stp)/cc) Q st (kj/mol) NU K 24 K 27 K ln(p) 5-1 a i e e-9 b i e e e Total Uptake (cc(stp)/cc /T Figure S33. Same as Fig. S28 but for NU-111. S26

27 Section 6. Pellets from compressed HKUST-1 powder; pore volumes and x-ray diffraction Here we show that the MF pellets collapses when they are pressed into pellets, losing their porosity and crystallinity with press. 6 5 V pore =.74 cc/g (HKUST1_powder) HKUST-1 powder.5 Tons Pellet 2 Tons Pellet 5 Tons Pellet N 2 Uptake (cc/g) V pore =.68 cc/g (Pellet_.5ton) V pore =.57 cc/g (Pellet_2ton) V pore =.32 cc/g (Pellet_5ton) X-ray intensity (arb.) Pressure (P/P ) Two theta (deg.) Figure S34. Left: The nitrogen isotherms on control sample (commercial HKUST-1, top) and on pressed pellet samples, showing that the pore volume decreases with increasing pressure. Right: X-ray patterns from the control sample (top) and the pellets, indicating that the peak-intensities decrease while the peakwidths increase with increasing pressure. S7. References 1. Wilmer, C. E.; Farha,. K.; Yildirim, T.; Eryazici, I.; Krungleviciute, V.; Sarjeant, A. A.; Snurr, R. Q.; Hupp, J. T. Energy Environ. Sci. 213, 6, Peng, Y.; Srinivas, G.; Wilmer, C. E.; Eryazici, I.; Snurr, R. Q.; Hupp, J. T.; Yildirim, T.; Farha,. K. Chem. Commun. 213, 49, Duerr, B. F.; Chung, Y. S.; Czarnik, A. W. J. rg. Chem. 1988, 53, Chen, Z.; Xiang, S.; Liao, T.; Yang, Y.; Chen, Y. S.; Zhou, Y.; Zhao, D.; Chen, B. Crystal Growth & Design 21, 1, Ma, S.; Sun, D.; Simmons, J. M.; Collier, C. D.; Yuan, D.; Zhou, H. C. J. Am. Chem. Soc. 28, 13, Walton, K. S.; Snurr, R. Q. J. Am. Chem. Soc. 27, 129, Zhou, W.; Wu, H.; Hartman, M. R.; Yildirim, T. J. Phys. Chem. C 27, 111, S27