H<sub>2</sub> and CH<sub>4</sub> Sorption on Cu-BTC Metal Organic Frameworks at Pressures up to 15 MPa and Temperatures between 273 and 318 K

doi:10.4236/jsemat.2011.12004

Paper Menu >>

Journal Menu >>

Journal of Surface Engineered Materials and Advanced Technology, 2011, 1, 23-29

doi:10.4236/jsemat.2011.12004 Published Online July 2011 (http://www.SciRP.org/journal/jsemat)

H2 and CH4 Sorption on Cu-BTC Metal Organic

Framewo rk s at Pressures up to 15 MPa and

Temperat ures between 273 and 318 K

Yves Gensterblum

Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Lochn er s tr Aachen, Germany.

Emai l: [email protected]

Received March 17th, 2011; revised May 31st, 2011; accepted Jun e 9th, 2011.

ABSTRACT

Sorption isotherms of methane and hydrogen on Cu3(BTC)2 have been measured in the temperature range from 273 to

318 K and a t pr essu res up to 15 MPa. H2 excess sorption capacities of the Cu3(BTC)2 amounted to 3.9 mg/g at 14 MPa.

Promising maximum CH4 excess so rption capacities on the same sample were reached at approximately 5 MPa. They

amounted to 101, 100, 92 and 80 mg/g at 273, 278, 293 and 318 K, respectively. The sorbed phase density was essen-

tially the same for all temperatures and amounted to ~600 kg/m3. Structural changes of the Cu3(BTC)2 samples after

thermal activation and treatment with high pressure H2 and CH4 were tested. It was found that the initial micropore

structure has virtually disappeared as evidenced by a decrease of the Langmuir specific surface area by a factor ~3 and

CO2 micropore volume by a factor of ~4 for H2 and ~3 for CH4. This is in line with a n inc rease in the average pore di-

ameter from in itially 9.2 to 15.7 for H2 and 12.8 for CH4.

Keywords: Metal Organic Framework (MOF), Sorption, Methane, Hydrogen, Pore Structure

1. Introduction

The concept of reticular design in the synthesis of metal

organic frameworks (MOF) permits custom-tailoring of

regular pore structures on the nanometer scale [1]. This

approach opens new perspectives for the development of

gas and energy storage systems [2]. So far, the ga s sorp-

tion capacity of metal-organic frameworks (MOF) of

various chemical and structural compositions has mainly

been determined at low pressures (< 0.1 MPa) and tem-

peratures (77 to 87 K). Only a few studies [3,4] reported

H2 and CO 2 measurements at ambient temperatures (ideal

operating temperature).

Several authors reported the internal structure of dif-

ferent MOFs [5,6]; however, significant amounts of side

products were detected using the synthesis described by

Chui et al. (1999)[5]. One major problem concerning the

storage of gases on these materials at high pr essur es (> 1

MPa) and temperatures (especially at the activation tem-

perature of 458 K) is their structural instability and

hence, a decrease in specific surface area associated with

struc- tural rearrangements for Cu-(BTC) [6].

In this study the sorption capacities of CH4 and H2 on

Cu3(BTC)2 (Copper benzene-1,3,5-tricarbox ylate,C18H6

Cu3O12) have been investigated at temperatures between

273 and 318 K and pressures up to 15 MPa. Specific

surface areas (SSA) and pore size distributions (PSD)

have been determined on untreated samples before and

after high-pressure sorption experiments in order to de-

tect any structural changes of the sample due to the in-

teraction with the gases. A similar approach has been

used by [7], who reported changes in SSA and PSD on

MOF-5 during hydrogen sorption.

Two slightly different MOFs both consist of the same

organic ligands but with different basic metals (Al3+ and

Cr3+) [8]. At 77K the Al3+–MOF shows higher sorption

capacities than the corresponding Cr3+ sa mp le. However,

both samples nearly show the same specific surface area

of ~1000 m2/g (Figure 1). This finding confirms the im-

portance of micropore volume and the electrostatical

potential of t he different metal s.

Data provided in Figure 1 reflects the general correla-

tion between SSA (determined by low pressure N2-iso-

therms at 77 K) and H2 sorption capacity at 77 K. It is

known that this trend is ambiguous for isotherms re-

corded at higher temperatures [9]. One suggestion is that

H2 and CH4 Sorption on Cu-BTC Metal Organic Frameworks at Pressures up to 15 MPa and Temperatures

between 273 and 318 K

[1] IRMOF-11

[1] IRMOF-6

[1] MOF-177

[1] IRMOF-1

[1] HKUST-1

[1] IRMOF-20

[3] Cu3BTC2

[3] MOF-5

[1] MOF-74

[8] MOF-53 Cr

[8] MOF-53 Al

[4]

0E+00

1E-02

2E-02

3E-02

4E-02

5E-02

6E-02

7E-02

8E-02

01000 2000 3000 4000 5000 6000

uptake / g g

-1

BET Surface area / m² g

-1

Figure 1. Comparison of high-pressure (~5 MPa) H2 sorp-

tion capacities at 77 K vs. N2-BET surface area for different

MOFs and carbon materials .

a better correlation can be obtained by separating the

hydrogen adsorbed in the micropores from that on the

surface of the mesopores. Furthermore, Nijkamp et al.

(2001) concluded that a higher storage capacity could be

achieved with adsorbents containing a large micropore

volume with suitable diameter [9].

In a st ud y on h ydr ogen stor ag e in c hemi call y ac tiva ted

carbons and carbon nanomaterials, Beneyto (2007) [10]

proposes that at 77 K the H2 adsorption capacity depends

on the SSA and the total micropore volume of the acti-

vated carbon. At 298 K it depends on both the micropore

volume and the micropore size distribution. To date, very

few high pressure/temperature isotherms and corre-

sponding micropore volumes have been determined on

MOFs.

In comparison to hydrogen, it was shown for methane

in different studies that Cu3(BTC)2 has a high CH4 stor-

age capacity at room temperature [11,12] (295 to 298 K,

Wang et al. 2002; Lin et al. 2006). Sorption values on

Cu-BTC for CH4 of up to 72 mg/g (at 295 K and 0.1

MPa) with nearly linear sorption isotherms up to 0.1

MPa [11]. Maximum CH4 sorption capacities of 31.4

mg/g at 0.9 MPa and 298 K on Zn–MOF and a hysteresis

between the sorption and desorption curves [12]. Senk-

ovska and Kaskel (2007) [13] reported high pressure CH4

adsorption on Cu3(BTC)2, Zn2(bdc)2dabco, Cr3F(H2O)2,

O(bdc)3. Among the three materials, Cu3(BTC)2 shows

the highest excess adsorption at 303 K (15.7 mg/g).

2. Experimental

2.1. High-Pressure Sorption Experiments

High pressure single-gas adsorption experiments have

been performed using a manometric experimental set-up

(Figure 2) consisting of a stainless-steel measuring cell

(MC) and a calibrated reference volume (RC) connected

with a set of actuator-driven valves and a high-precision

gas

supply

pressure

Figure 2 . S che mat i c diag r a m of s or pti o n a p par at us us e d fo r

high pressure/high temperature H2 and CH4 sorption ex-

periments on Cu-BTC MOFs. (RC = calibrated reference

volume ; MC = measuring cell).

pressure transducer (max. pressure 25 MPa, with a preci-

sion of 0.05% of the full scale value). The entire device

is placed in a temperature-controlled oven (variations in

temperature < 0.1 K). Calculation of the excess sorption

was performed based on equations of state by Setzman

and Wagner (1991) [14] and McCarty et al. (1981) [15]

for methane and hydrogen, respectively. Quality control

is ensured by participation in laboratory comparison

studie s (e. g. Gensterblum et a l. 2009 [16], 2010 [17] and

Goodman et al. 2004 [18]). For further details on the

experimental approach, please refer to e.g. Busch et al.

(2004) [19].

As pointed out by Férey (2003) [8] for the MIL-53 and

Schlichte et al. (2004) [6] for the MOFs - which were

also investigated in this study - the activation of the

metal-organic framework compounds is an important

issue affecting the qualit y and rep roducibilit y of sorption

capacity measurements. The activation procedure was

carried out in three stages: 12 h at 105˚C, 12 h at 155˚C,

and finally 18 h at 185˚C. This activation procedure led

to well-reproducible starting conditions for the isotherm

measurements.

Error bars shown in the diagrams and error margins

listed in the Table 2 were determined based on the Gauss

error propagation method considering the individual er-

rors of the individual experimental parameters.

2.2. Characterisation of Pore Structure and

Surface Area

A Quantachrome Autosorb 1 instrument was used to

characterise the pore structure and surface properties of

the samples. The latter has been performed using the

equation proposed by Brunauer, Emmet and Teller

(1938, BET) [20]. The pore size distribution for 1.2 up to

40 nm pore diameters were derived by N2-isotherms

measured at 77 K. Pore size distributions (PSD) were

analysed [21,22] and the nonlinear density functional

theory (NLDFT, Thommes et al. 2006) [ 23]. The submi-

cro- and micropores, in the range of 0.3 to 1.5 nm, were

charac- terised by CO2 isotherms measured at 273 K.

These iso- therms were also evaluated according to the

Dubinin and NLDFT methods. For the NLDFT evalua-

tion, slit and/or cylindrical pores were assumed which

H2 and CH4 Sorption on Cu-BTC Metal Organic Frameworks at Pressures up to 15 MPa and Temperatures

between 273 and 318 K

represents a com- promise between availability of

mathematical PSD-al- gorithms with spherical pore

structure and real pore structures.

3. Results and Discussion

3.1. Sorption Capacities

3.1.1. Hydrogen

Figure 3 shows the H2 excess sorption isotherms for

Cu3(BTC)2 (HKUST-1), measured at 318 K, in compare-

son with similar literature data reported for Cu3(BTC)2 at

298 K [7]. The higher sorption capacities reported by

Panella et al. (2005) [7] can be explained by lower ex-

perimental temperatures used. The rather linear trend

(Freundlich or Langmuir-Freundlich type) of the sorption

isotherms is comparable to other isotherm data (see Fig-

ure 1), but it is not a cla ssical Langmuir type as would be

expected for porous materials.

Structural changes (pore structure, specific surface

area) of the Cu3(BTC)2 after H2 sorption have been de-

termined; the results are provided in Table 1. It is obvi-

ous that specific surface areas (SSA) decrease by a factor

of 3-4, N2 pore volumes by a factor of 2-3, and CO2 mi-

cropore volumes by a factor of 4-5, while an increase in

the Dubinin-Astakhov (DA) average pore diameter from

9.2 to 15.7 Å (10−10 m) can be observed.

Compared to the N2 micropore volumes for Cu3(BTC)2

determined in this study 0.63 cm3g−1 (Table 1), several

authors obtained values between 0.41 and 0.76 cm3g−1 on

virgin samples [13,24,25]. Other studies report BET sur-

face areas for this material of 1781 m2/g (single-point

BET) [26], 1154 m2/g [7] and 1239 m2/g [11] which is

similar to the BET surface area of 1246 m2/g ascertained

in this study (all measured wit h N2 at 77 K).

3.1.2. Met hane

Methane sorption isotherms on Cu3(BTC)2 have been

measured at temperatures between 273 and 318 K and

pressures up to 15 MPa and are provided in Figure 4.

Maximum excess sorption values obtained in these

measurements are listed in Table 2. They show a gene-

rally decreasing trend with temperature from 101 to 79

mg CH4/g MOF. After passing a maximum value, the

excess sorption isotherms in Figure 4 decrease slightly

until the final pressure value is reached. This decline

above ~6 MPa can be attributed to a volumetric effect

(non-negligibl e volume of the sorbed phase) that needs to

be considered when calculating absolute sorption capaci-

ties. Among others, Humayun and Tomasko (2000) [27]

proposed a method to determine the sorbed phase density,

which has been applied in this study. This procedure re-

sulted in nearly identical values of 597 to 601 kg/m3 for

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

036912 15

excess s or ption / mg g

-1

Pressure / MPa

this study (318K)

Panella et al.(2006) (298K)

Figure 3. H2 excess sorption capacity measured at 318K on

Cu3(BTC)2. For comparison the H2 excess sorption data at

298 K on Cu3(BTC)2 reported by Panella et al.7 has been

included.

Table 1. Structural cha nges of Cu3(BTC)2 after high-pressure H2 s orpt ion e x peri ment at 318 K. DR = Dubinin R ad ushkewic;

NLDFT = non-local density functional theory.

Cu3(BTC)2 method N2 surface area

(m2/g) CO2 micropore surface

area (m2/g) N2 pore volume

(cm3/g) CO2 micropore

volume (cm3/g) DA pore

diam et er (Å)

befor e H2 sor ptio n test DR

NLDFT 1731

1994 2708

2340 0.63

0.64 0.94

0.89 9.2

after H2 sorption test DR

NLDFT 651

576 752

641 0.23

0.33 0.26

0.20 15.7

Table 2. CH4 Sorptio n p arameters of Cu3(BTC)2 at 273 to 318 K considering helium densities.

T (K) max. excess CH4 sorption capacity (mg/g) absolute CH4 sorption capa city (mg/g) CH4 sor be d phase de ns i ty (kg / m 3)

273 101 ± 7 11 3 ± 3 599 ± 10

278 100 ± 7 11 2 ± 3 601 ± 8

293 92 ± 2 103 ± 2 59 7 ± 5

318 79 ± 2 90 ± 3 n.d.

H2 and CH4 Sorption on Cu-BTC Metal Organic Frameworks at Pressures up to 15 MPa and Temperatures

between 273 and 318 K

100

120

036912 15

Pressure / MPa

Excess sorption / mg g

-1

273K

Langmuir fit 273K

278K

Langmuir fit 278K

293K

Langmuir fit 293K

318K

Langmuir fit 318K

Figure 4. CH4 sorption isotherms measured on Cu3(BTC)2

at 273, 278, 293, and 318 K.

the CH4 sorbed phase density at three of the four experi-

mental temperatures (Figure 5, Table 2). For the iso-

therm measured at 318 K, the pr essure i s not high enough

for a graphical d etermination. This suggests that t he den-

sity of the sorbed CH4 phase is independent of the ex-

perimental temperature. Maximum absolute sorption

capacities, taking into consideration the volume of the

sorbed phase, have been determined to be as high as 113,

112, 103 and 90 mg/g at 273, 278, 293 and 318 K, re-

spectively (Table 2), by applying the following relatio n-

ship:

abs gas

sorbed

nap



=





−



(1)

where

denotes the excess sorption capacity,

gas

the gas phase density, “

” is the Langmuir parameter

(1/MPa) and sorbed

the sorbed phase density as deter-

mined graphically in Figure 5.

The Langmuir curves shown in Figure 4 were calcu-

lated with explicit consideration of the sorbed phase den-

sity and therefore, reproduce the decline of the isotherms

at high pressures.

In comparison to the study by Senkovska and Kaskel

(2007) [13], the CH4 sorption values in this study are

lower by a factor of ~1.4. One explanation might be the

reference to the sample mass (or sample density). Sen-

kovska and Kaskel (2007) [13] used a crystallographic

density of 0.88 g/cm3. In this study, sorption values are

related to initial weight, while the sample density after

activation is 1.77 ± 0.03 g/cm³ as determined by helium

pycnometry. This lead to a slightly lower sorption

amounts for this study in comparison to Senkovska and

Kaskel (2007) [13].

100

120

0100 200300 400500 600700

excess sorpt ion / mg g

-1

Gasphas e dens ity / kg m

273K

278K

293K

318K

Figure 5. CH4 excess sorption capacities vs. CH4 gas phase

density at different temperatures (Cu3(BTC)2.

3.2. Isosteric Heats of Adsorption

Based on the sorption isotherms measured between 273

and 318 K, isosteric heats of adsorption for CH4 have

been calculated using the Clausius-Clapeyron relation

(Equation (2)). In this first approximation, the depen-

dence of the adsorption enthalpy on surface coverage

was neglected.

12212 1

21121 2

ln ln

ads R TTpR TTa

hTTpTT a

 

⋅⋅

∆= =

 

−−

 

(2)

where T1 and T2 are 273 and 318 K, respectively, p1 and

p2 are the CH4 pressures for each isotherm corresponding

to an equal fractional coverage Θ and R denotes the uni-

versal gas constant. The parameters a1 and a2 are con-

stant s de rived fr om t he li near ise d La ngmu ir c urve for the

two temperatures. For further details, please refer to Pa-

nella et al. (2006) [3].

The isosteric heat of adsorption was calculated based

on a Langmuir fit of the experimental data. The decrease

in CH4 excess sorption at pressures above 10 MPa is re-

produced by introducing a term that accounts for the in-

crease in sorbed phase volume with increasing loading

(Equation (1)). For this purpose, the density of the sorbed

phase was determined graphically (see Figure 5). The

procedure resulted in a very good fit (Figure 4) of the

experimentally determined excess sorption values. The

Langmuir parameters a1 and a2 obtained with this met ho d

for isotherms at two different temperatures were used in

Equation (2) for the calculation of the isosteric heat of

adsorption.

Isosteric heats of adsorption for CH4 show an average

value of −11.2 ± 0.7 kJ/mol. In this case, a constant den-

sity of the sorbate phase was assumed. Using the pa-

rameters for the best least square Langmuir fit, an aver-

age value of −12.2 ± 0.7 kJ/mol was obtained. Evaluation

of the isosteric heat of adsorption in the low pressure

H2 and CH4 Sorption on Cu-BTC Metal Organic Frameworks at Pressures up to 15 MPa and Temperatures

between 273 and 318 K

range (0 - 4 MPa) w

the linearised Langmuir fit (pro-

viding the same values of absolute adsorption as the

graphical evaluation) results in a significantly higher

value for the heat of adsorption (−17.9 ± 1.3 kJ/mol).

3.3. Impact of CH4 Sorption on Pore-Size

Distribution

The pore-size distributions of the initial Cu3(BTC)2 and

the samples after successive CH4 and H2 sorption mea-

surements were determined by N2 adsorption at 77 K. In

order to describe adsorption on a wider range of mic-

roporous materials the Dubinin-Astakhov (DA) equation

was used (Dubinin and Astakhov, 1971) [21]. It is a ge-

neralized form of the Dubinin-Radushkevich (DR; Du-

binin, 1975 [22]) equation and was found to reasonably

fit adsorption data for heterogeneous micropores. The

resul ts of the evaluatio ns according to the DA method are

displayed in Figure 6; the pertaining fitting parameters

are listed in Table 3. The heterogeneity value (n) is

higher for homogeneous distributions and is typically

between 1 and 3. For instance, zeolite has an n-value

higher t han 3, d e monstrating that these materials are very

homogeneous. In this study, a value of n = 1 was dete r-

mined for Cu3(BTC)2. The characteristic energy E after

Dubinin (1975) was determined to be 20.97 kJ/mol for

the initial (unspoiled) sample and ranged between 8 and

18 kJ/mol after high-pressure CH4 and H2 sorption tests.

The interaction constant is given as k = 2.96 kJ·nm3/mol

for nitrogen.

From Figure 6 it is evident that CH4 affects the stabi-

lity of the MOF to a lesser extent than H2. Although a

significant decrease in total pore volume is shown after

two successive CH4 sorption experiments, accompanied

by a shift to larger mean pore radii (4.7 Å for the original

sample; 6 . 4 Å afte r si x CH4 so rptio n isother ms; Table 3),

a reduction comparable to the H2 treatment is only ob-

served after 6 CH4 sorption isotherms. As observed for

the H2 treatment, the pore volume in the 5 to 15 Å range

is most heavily affected. In this study it is likely that we

had chosen a slightly too high activation temperature.

However the reason for the different influence of CH4

and H 2 on the sample structure is not clear will be invest-

tigated in further detail in a fol low-up st udy.

Results of the evaluation of the micropore structure of

the Cu3(BTC)2 before and after high-pressure CH4 sorp-

tion i so therms b ase d o n the D R met hod a nd the no nl i near

density functional theory (NLDFT) are summarised in

Table 4 . The se results a lso supp ort a signi fica nt decrease

in micropore volume and subsequent reduction in spe-

cific surface area of the sample after high-pressure CH4

sorptio n tests.

Figure 7 compares the high-pressure CH4 exce ss sorp-

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

010 20 30 40 50 60

Differential pore volume / cm³ g

-1

Pore diameter / A

initial sa mp le

after 2 CH4 s orption cycles

after 6 CH4 s orption cycles

after 2 H2 s orption cycles

Figure 6. Dubinin Astakov differential pore volume distri-

butions of Cu3(B TC)2 before and after high-pressure CH4

and H2 sorption isotherms. Evaluation based on low-pres-

sure N2-sorption at 77 K.

100

120

0246810 12 14 16

excess sorpt ion / mg g

-1

Pressure / MPa

initial sa mp le

after treatment

∆m = 39.7 mg g

-1

Figure 7. Comparison between initial and CH4 treated

Cu3(BTC)2 at 293 K.

tion isotherms measured on the initial Cu-BTC MOF

with a decomposed sample of the same material at 293

K. The treated sample shows significantly lower sor ption

values (decrease of up to 40 mg/g) compared to the ini-

tial samples, while the shape of the isotherms is similar

between the two isotherms.

4. Conclusions

At pressures up to 7 MPa, Cu-BTC MOF is one of the

most promising MOF materials for metha ne storage with

a large uptake capacity and an excess sorption of 9.2

wt% at 293 K. The repeated thermal activation and high-

pressure sorption tests with CH4 on HKUST-1 at tem-

peratures between 273 and 318 K resulted in a reduction

of specific micropore volumes and surface area. The

processes behind the reduction of the specific micropore

volumes and surface area during each CH4 sorption test

(Table 4) are ambiguous and further research on this

topic is needed.

Recent studies indicate ther mal deter ioratio n effect s and

H2 and CH4 Sorption on Cu-BTC Metal Organic Frameworks at Pressures up to 15 MPa and Temperatures

between 273 and 318 K

Table 3. Fitting parameters of the DA equation for micropore characterisation of Cu3(BTC)2 before and after CH4 and H2

high-pressure sorpt ion i sotherms.

Cu3(BTC)2 N2 char acteristi c energ y E [kJ/mol] DA h etero geneous va l ue n average pore radius [Å]

initial sample 20.97 1 4.7

after 2 Ch4 isotherms 18.66 1 4.9

after H2 isotherms 11.17 1 5.8

after 6 CH4 isotherms 8.66 1 6.4

Table 4. Results of pore structure analysis of Cu3(BTC)2 before and after high-pressure so rption isotherms with CH4.

method N2 surface ar ea

(m2/g) N2 pore volume

(cm3/g) CO2 surface area

(m2/g) CO2 micropore

volume (cm3/g) N2 DA por e

dia meter (Å)

initial sample DR

NLDFT 1731

1994 0.62

0.64 2708

2340 0.94

0.89 9.2

after 2 CH4 isotherms DR

NLDFT 1174

1186 0.42

0.55 1226

1069 0.43

0.35 12.4

after 6 CH4 isotherms DR

NLDFT 737

591 0.26

0.48 997

887 0.35

0.28 12.8

by interaction with atmospheric air could cause the ob-

served degradation of the sample.

Table 4 shows a stepwise deterioration of the sample

after successive CH4 sorption isotherms and the thermal

activation process on the identical sample. Further

changes caused by exposure to the atmosphere (e.g. oxi-

dation of the sample) can be neglected, since samples did

not come in contact with atmospheric air from the begin-

ning of the thermal activation process (only H2, CH4 and

He). However, it is unclear as of yet why micropores

volumes decrease drastically and larger pores remain

preserved.

Finally, this study has shown that the CH4 sorbed

phase density is, within reasonable errors, independent of

temperature.

5. Acknowledgments

I am greatly indebted to Stefan Kaskel for providing

2007 the samples and Joachim Borchardt for technical

support. The fruitful discussion and remarks of Bernd

Krooß, Andreas Busch, Susan Giffin and Dirk Prinz are

greatly appreciated.

REFERENCES

[1] M. Eddaoudi, J. K im, N. Rosi, D. Vodak, J. Wachter, M.

O’Keeffe and O. M. Yaghi, “Systematic Design of Pore

Size and Functionality in Isoreticular MOFs and Their

Application in Methane Storage,” Science Magazine, Vol.

295, No. 5554, 2002, pp. 469-472.

doi:10.1126/science.1067208

[2] N. Amaroli and V. Balzani, “The Future of Energy Sup-

ply: Challenges and Opportunities,” General and

Introdu ctory Chemistry, Vol. 46, No. 1-2, 200 7, pp. 52-66.

doi:10.1002/anie.200602373

[3] B. Panella, M. Hirscher, H. Pütter and U. Müller,

“Hydrogen Adsorption in Metal-Organic Frameworks:

Cu-MOFs and Zn-MOFs Compared,” Advanced Func-

tional Material s, Vol. 16, No. 4, 2006, pp. 520-524.

doi:10.1002/adfm.200500561

[4] H. Li, M. Eddaoudi, M. O’Keeffe and O. M. Yaghi,

“Design and Synthesis of an Exceptionally Stable and

Highly Porous Metal-Organic Framework,” Nature, Vol.

402, pp. 276-279. doi:10.1038/46248

[5] S. Y. Chui, et al., “A Chemically Functionalizable

Nanoporous Material [Cu3(TMA) 2(H2O)3]n,” Science

Magazine, Vol. 283, No. 54 05 , 1999,pp. 1148-1150.

doi: 10.1126/science.283.5405.1148

[6] K. Schlichte, T. Kratzke and S. Kaskel, “Improved

synthesis, Thermal Stability and Catalytic Properties of

The Metal -Organi c Framework Compound Cu3(BTC)2,”

Micro porous and Mesoporous Materials, Vol. 73, No. 1-2,

2004, pp. 81-88. doi:10.1016/j.micromeso.2003.12.027

[7] B. Panella and M. Hirscher. “Hydrogen Physisorption in

Metal-Organi c Porous Systems,” Adva nced Material, Vol.

17, No. 5, 2005, pp. 538-541.

doi:10.1002/adma.200400946

[8] G. Férey, M. Latroche, C. Serre, F. Millange, T. Loiseau

and A. Percheron-Guégan, “Hydrogen Adsorption in the

Nanoporous Metal-Benzenedi carboxylate M(OH)(O2C–

C6H4–CO2)(M = Al3+, Cr3+), MIL-53,” Chemical Com-

munications, No. 24, 2003, pp. 2976-2977.

doi: 10.1039/B308903G

[9] M. G. Nijkamp, J. E. M. J. Raaymakers, A. J. van Dillen

and K. P. de Jong “Hydrogen Storage Using

Physisorption – Materials Demands,” Applied Physics A

Materia ls Sci ence & Processing , Vol. 72, No. 5 , 2001, pp.

H2 and CH4 Sorption on Cu-BTC Metal Organic Frameworks at Pressures up to 15 MPa and Temperatures

between 273 and 318 K

619-623.

[10] J. Beneyto, F. Suárez-García, D. Lozano-Castelló, D.

Cazorla-Amorós and A. Linares-Solano, “Hydrogen

Storage on Chemically Activated Carbons and Carbon

Nanomaterials at High Press ures,” Carbon, Vol. 45, No. 2,

2007, pp. 293-303. doi:10.1016/j.carbon.2006.09.022

[11] Q. M. Wang, D. Shen, M. Bulow, M. L. Lau, S. Deng, F.

R. Fitch and N. O. Lemcoff, J. Semanscin,

“Metallo-Organic Molecular Sieve for Gas Separation

and Purification,” Microporous and Mesoporous Mate-

rials, Vol. 55, No. 2, 2002, pp. 217-230.

doi:10.1016/S1387-1811(02)00405-5

[12] X. Lin, A. J. Blake, C. Wilson, X. Z. Sun, N. R.

Champness, M. W. George, P. Hubberstey, R. Mokaya

and M. Schroder, “A Porous Framework Polymer Based

on a Zinc(II) 4,4’-Bipyridine-2,6,2‘, 6‘-Tetracarboxylate:

Synthesis, Structure, and ‘Zeolite-Like’ Behavio r s ,”

Journal of American Chemical Society, Vol. 128, No. 33,

2006, pp. 10745-10753. doi:10.1021/ja060946u

[13] J. Senkovska and S. Kaskel, “High Pressure Methane

Adsorption in the M etal-Organic Frame works Cu3(BTC)2,

Zn2(bdc)2dabco, and Cr3F(H2O)2O(bdc)3,” Microporous

and Mesoporous Materials, Vol. 112, No. 1-3, 2008, pp.

108-115. doi:10.1016/j.micromeso.2007.09.016

[14] U. Setzmann and W. Wagner, “A New Equation of State

and Tables of Thermodynamic Properties for Methane

Covering the Range From the Melting Line to 625 K at

pressures up to 1000 MPa,” Journal of Physical and

Chemical Reference Data , Vol. 20, No. 6, 1991, pp.

1061-1155. doi:10.1063/1.555898

[15] R. D. McCarty and V. D Arp , “A New Wide Ran ge Equ-

ation of State for Helium,” Advances in Cryogenic Engi-

neerin g, Vol. 35, 1990, pp. 1465-1475.

[16] Y. Gensterblum, P. van Hemert, P. Billemont, A. Busch,

D. Charriere, D. Li, B. M. Krooss, G. de Weireld, D.

Prinz and K.-H. A. A. Wolf, “European Inter-Laboratory

Comparison of High Pressure CO2 Sorption Isotherms. I:

Activated Carbon ,” Carbon, Vol. 47, No. 13, 2009, pp.

2958-2969. doi:10.1016/j.carbon.2009.06.046

[17] A. L. Goodman, A. Busch, G. Duffy, J. E. Fitzgerald, et

al., “An Inter-laboratory Comparison of CO2 Isotherms

Measured on Argonne Premium Coal Samples,” Energy

and Fuels, Vol. 18, No. 4, 2004, pp. 1175-1182.

doi:10.1021/ef034104h

[18] Y. Gensterblum, P. Van Hemert, P. Billemont, et al.,

“European inter-laboratory comparison of high pressure

CO2 sorption isotherms II: Natural coals,” International

Journal of Coal Geology, Vol. 84, No. 2, 2010, pp.

115-124. doi:10.1016/j.carbon.2009.06.046

[19] A. Busch, Y. Gensterblum, B. M. Krooss and R. Littke,

“Methane and Carbon Dioxide Adsorption-Diffusion Ex-

periments on Coal: An upscaling and Modelling,” Inter-

national Journal of Coal Geology, Vol. 60, No . 2-4, 2004,

pp. 151-168. doi:10.1016/j.coal.2004.05.002

[20] S. Brunauer, P. H. Emmett and E. Teller, “Adsorption of

Gases in Multimolecular Layers,” Journal of American

Chemical Society, Vol. 60, No. 2, 1938, pp. 309-319.

doi:10.1021/ja01269a023

[21] M. M. Dubinin, “Physical Adsorption of Gases and Va-

pors in Micropo res,” Acade mic Press, New York, 1975, p.

1-70.

[22] M. M. Dubinin and V. A. Astakhov, “Description of Ad-

sorption Equilibria of Vapors on Zeolites over Wide

Ranges of Temperature And Pressure,” Advances in

Chemistry, Vol. 102, No. 69, 1971, pp. 65-69.

doi:10.1021/ba-1971-0102.ch044

[23] M. Thommes, B. Smarsly, M. Groenevolt, P. I. Ravi-

kovitch and A.V. Neimark, “Adsorption Hysteresis of

Nitrogen and Argon in Pore Networks and Cha-

racterization of Novel Micro- and Mesoporous Silicas,”

Langmuir, Vol. 22, Vol. 2, 2006, pp. 756-764.

doi:10.1021/la051686h

[24] M. Kramer, U. Schwarzer, S. Kaskel, “Synthesis and

properties of the metal-organic framework Mo3(BTC)2

(TUDMOF-1)” Journal of Material Chemistry, Vol. 16,

2006, pp. 2245-2248. doi:10.1039/b601811d

[25] P. Krawiec, M. Kramer, M. Sabo, R. Kunschke, H. Fröde

and S. Kaskel, “Improved Hydrogen Storage in the

Metal-Organic Framework Cu3(BTC)2” Advanced Engi-

neering Material, Vol. 8, No. 4, 2006, pp. 293-296.

doi:10.1002/adem.200500223

[26] A. R. Millward and O. M. Yaghi, “Metal-Organic

Frameworks with Exceptionally High Capacity for

Storage of Carbon Dioxide at Room Temperature,”

Journal of American Chemical Society, Vol. 127, No. 51,

2005, pp 17 998-17999. doi:10.1021/ja0570032

[27] R. Humayun, D. L. Tomasko, “High-Resolution Adsorp-

Tion Isotherms of Supercritical Carbon Dioxide on Acti-

vated Carb on,” A ICHE Journal, Vol. 46, No. 10, 2000,pp.

2065-2075. doi:10.1002/aic.690461017