research article molecular simulation of hydrogen storage...

Research ArticleMolecular Simulation of Hydrogen Storage inIon-Exchanged X Zeolites

Xiaoming Du

School of Materials Science and Engineering Shenyang Ligong University Shenyang 110159 China

Correspondence should be addressed to Xiaoming Du du511163com

Received 5 May 2013 Revised 15 October 2013 Accepted 18 October 2013 Published 6 January 2014

Academic Editor Jie Dai

Copyright copy 2014 Xiaoming DuThis is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Grand Canonical Monte Carlo (GCMC) method was employed to simulate the adsorption properties of molecular hydrogenon ion-exchanged X zeolites at 100ndash293K and pressures up to 10MPa in this paper The effect of cation type temperature andpressure on hydrogen adsorption capacity heat of adsorption adsorption sites and adsorption potential energy of ion-exchangedX zeolites was analyzed The results indicate that the hydrogen adsorption capacity increases with the decrease in temperaturesand the increase in pressures and decreases in the order of KX lt LiX lt CaX The isosteric heat of adsorption for all the threezeolites decreases appreciably with the increase in hydrogen adsorption capacityThe hydrogen adsorption sites in the three zeoliteswere determined by the simulated distribution of hydrogen adsorption energy and the factors that influence their variations werediscussed Adsorption temperature has an important effect on the distribution of hydrogen molecules in zeolite pores

1 Introduction

The utilization of hydrogen as a possible substitute for fossilfuels requires the solution of a number of problems relatedto hydrogen production transportation storage and fuel celltechnology [1] Among them safe and efficient storage ofhydrogen is very important for hydrogen energy applicationsVarious methods for storing hydrogen were developed whichinclude high-pressure tanks for gaseous hydrogen cryogenicvessel for liquid hydrogen and metal hydride for solid-state storage systems [2ndash4] The first two methods bear thedanger of explosion if handled improperly and the latter onesuffers high cost and weight Recently attention has beenfocused on light microporous materials such as carbon [5]aluminosilicate zeolites [6 7] and metal organic frameworks(MOFs) [8] for storing hydrogen by adsorption because theadsorption is reversible and thus the sorbent can be recycled

Zeolites are a large class of crystalline aluminosilicatematerials that have high thermal stability and regular andsingle size pores and the diameter of the pores can be con-trolled by changing the size and charge of the exchangeablecations Thus they offer enormous potential for storage ofgases The hydrogen storage capacity of various types ofzeolites had been reported experimentally and theoretically

[9ndash12] However little attention was previously paid to thedistribution of adsorption sites and adsorption potentialenergy for the molecular hydrogen on zeolites Li and Yang[13] reported experimentally that the alkali-metal cations(Li+ Na+ K+) and the framework atoms (Al O Si) inion-exchanged X zeolites were the main adsorption sites ofhydrogen Kazansky et al [14 15] investigated the adsorptionsites of hydrogen on ion-exchanged X and Y zeolites withvarious SiAl ratios by using sorption and DRIFT spectramethods The results indicated that the adsorbed hydrogenis located mainly at site II and site III inside the FAU zeolitesupercages

However the studies on hydrogen storage in X type ofzeolites are so far only limited to the conditions of the separatetemperatures and low pressure owing to not being readilyamenable to experiments It is disadvantageous for our in-depth understanding of the mechanism of hydrogen storagein zeolites Molecular simulation can provide a cost-effectiveway of determining adsorption isotherms and gives a usefulinsight into the adsorption behavior of molecular hydrogeninside zeolite channels and pores

In this study we performed the adsorption simulationof hydrogen on three alkali-metal and alkali-earth cations(Li+ K+ Ca2+) exchanged X zeolites at the temperatures of

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2014 Article ID 189745 10 pageshttpdxdoiorg1011552014189745

2 Advances in Materials Science and Engineering

100ndash293K and the pressures up to 10MPa by using GrandCanonical Monte Carlo (GCMC) method The dependenceof the hydrogen adsorption capacity of zeolites on tempera-ture pressure cation type adsorption site distribution andadsorption potential energy was discussed

2 Computational Details

Structures of the initial unit cell of alkali-metal and alkali-earth metal cations (Li+ K+ Ca2+) exchanged X zeolites suchas LiX KX and CaX (X = Si

96Al96O384

SiAl = 10) wereconstructed according to the results of X-ray crystallographicstudies [16ndash18] The crystal is cubic with unit cell parameters119886 = 25099 A and space group Fd-3 In dehydrated LiXzeolite there are three Li+ cation sites 32 Li+ cations arelocated in site I1015840 (in the120573-cage close to the hexagonal windowto the hexagonal prism) site II (in the six-member ring ofthe 120573-cage) and site III (in the supercage close to a squarewindow between two other square windows) respectivelyIn dehydrated KX zeolite there are four K+ cation sitesThe occupancies of these K+ cations at cation sites I (in thehexagonal prism) I1015840 II and III in zeolite KX are 16 16 32and 32 respectively For the dehydrated CaX zeolite the Ca2+cations are located in site I (12 Ca2+ cations) site I1015840 (4 Ca2+cations) and site II (32 Ca2+ cations) After constructingthe initial structure we performed energy minimizationcalculations to determine the equilibrium structures usingdensity function theory (DFT) method that was successfullyused to explore hypothetical FAU with dense topologies [19]DFT calculations were carried out with the code Quantum-ESPRESSO [20] which uses atom centered basis functionsthat are particularly efficient for total energy studies of verylow density materials with very large unit cells PeriodicDFT calculations were carried out using the PBE exchangecorrelation functional within the GGA approximation Thezeolites with minimized energy were used as adsorbents forhydrogen adsorption

For hydrogen adsorption on LiX KX and CaX zeolitesthe force field used was an enhanced version of the polymerconsistent force field (PCFF) [21] Because the host of X zeo-lite was treated as a rigid structure with fixed atom positionsobtained from theminimized structure at all simulations thetotal energy of the zeolite framework and adsorbedmolecules(119864total) is expressed as the sum of the short-range van derWaals (vdW) nonbond interaction energy (119864vdW) and thelong-range coulombic interaction energy (119864c)

119864total = 119864vdW + 119864c (1)

The vdW interactions between hydrogen and the zeoliteframework atoms are represented by Lennard-Jones (LJ)potential with the following expression

119864vdW = sum119894

sum

119895gt119894

(4120576119894119895[(

120590119894119895

119903119894119895

)

12

minus (

120590119894119895

119903119894119895

)

6

]) (2)

where 120576119894119895and 120590

119894119895are the LJ potential parameters that were

obtained from 120576119894and 120590

119894of each species by using the Lorentz

Berthelotmixing rule (ie a geometric combining rule for the

Table 1 Lennard-Jones parameters used for hydrogen adsorptionon ion-exchanged X zeolite

Atom type 120576 (kcalmol) 120590 (oplus) ReferenceH 00726 2958 [22]Si 00370 0076 [23]Al 00384 1140 [23]O 03342 3040 [23]Li 00249 2180 [24]K 00356 3020 [24]Ca 01553 2980 [24]

energy and an arithmetic one for the atomic size 120576119894119895= radic120576119894 sdot 120576119895

and 120590119894119895= (120590119894+ 120590119895)2) 119903

119894119895is the interatomic distance between

the 119894th and 119895th atomsThe LJ potential parameters used in allsimulations were summarized in Table 1

The coulombic electrostatic interaction energy is thelong-range interaction and the model systems are periodicSo Ewald sum was used for 119864c

119864c = sum119894

sum

119895gt119894

119902119894119902119895

119903119894119895

(3)

where 119902119894and 119902119895are the net atomic charges of the 119894th and 119895th

atoms respectivelyFor the assignment of charges of extraframework cations

Li+ K+ and Ca2+ and framework atoms Si Al and O thevalues of charges were obtained by using the electronegativityequalization method (EEM) which are taken from theliterature as given in Table 2 [25]

For hydrogen we used three-point charge model [23 2627] where the two outer sites are separated by a distance of119897 = 07414 A having a charge of 119902 = minus021119890 [28] and the thirdmidpoint has a point charge of minus2119902

All GCMC simulations were performed by employingthe Multipurpose Simulation Code (MUSIC) [29] The load-ing at a constant pressure and temperature was calculatedby attempting with equal probability to insert delete ortranslate one H

2molecule in the simulation cell Trial moves

considered here were the translation insertion and deletionof particles [30 31] The moves for each run were randomlychosen with equal probability The random movements ofmolecules make new configurations which may be acceptedaccording to Metropolisrsquos sampling scheme Each structuremodel consists of one elementary cell with three-dimensionalperiodic boundary conditionsThe cut-off distance for short-range LJ summation was set to 12 oplus which is less than halfof the length of the simulation box (25099 A) and the half ofthe cell length for Ewald summation was used The numberof GCMC steps was set to 2 times 107 for each simulation Thenumber of trial moves in an MC cycle is equal to the numberof adsorbed molecules Usually approximately 15 of thecycles were performed for equilibration and the subsequentcycles were used for statistics The simulation temperaturesincluded 6 temperatures 100K 140K 195 K 230K 260Kand 293K

Advances in Materials Science and Engineering 3

Table 2 The atomic charges q for elements of the three zeolite modelsa

Zeolite 119902Si(119890) 119902Al(119890) 119902O(1)(119890) 119902O(2)(119890) 119902O(3)(119890) 119902O(4)(119890) 119902Li(I1015840 IIIII)(119890) 119902K(I1015840 IIIII)(119890) 119902Ca(II1015840 II)(119890)

LiX 126853 112745 minus083069 minus085591 minus082155 minus088782 10 mdash mdashKX 127615 113366 minus087774 minus084282 minus079500 minus089425 mdash 10 mdashCaX 128523 113767 minus074562 minus100346 minus088257 minus079125 mdash mdash 20aIn Li+ K+ and Ca2+ cations exchanged X zeolites there are four oxygen sites O(1) O(2) O(3) and O(4)

0

2

4

6

8

10

Pressure (MPa)

H2

adso

rptio

n (m

molmiddotgminus1)

0 2 4 6 8 10 12 14

100 K140 K195 K

230 K260 K293 K

(a)

0

2

4

6

8

H2

adso

rptio

n (m

molmiddotgminus1)

100 K 230 K260 K293 K

Pressure (MPa)0 2 4 6 8 10 12 14

140 K195 K

(b)

0

2

4

6

8

10

12

14

H2

adso

rptio

n (m

molmiddotgminus1)

100 K 230 K260 K293 K

Pressure (MPa)0 2 4 6 8 10 12 14

140 K195 K

(c)Figure 1 Calculated hydrogen adsorption isotherms for (a) LiX zeolite (b) KX zeolite and (c) CaX zeolite

3 Results and Discussion

The hydrogen adsorption isotherms of LiX KX and CaXzeolites calculated at the temperatures of 100ndash293K and thepressures up to 10MPa with GCMC method were shown inFigure 1 All adsorption isotherms obtained under this studyare Type I in nature showing adsorption of hydrogen insidemicroporous zeolite cavities As can be seen in Figure 1 the

hydrogen adsorption capacity in terms of mmolg decreaseswith increasing temperature within the simulation temper-ature range The reason is that the hydrogen moleculeshave higher kinetic energy at higher temperature thus it isrequired for the larger adsorption potential energy to adsorbhydrogen molecules in zeolite cavities The effect of pressureonhydrogen adsorption capacity has two-step characteristicsNamely the hydrogen adsorption capacity rapidly increases


0

03

06

09

12

15

Pressure (MPa)

LiXKXCaX

H2

mol

ecul

esc

harg

e

0 2 4 6 8 10 12

Figure 2 Number of adsorbed hydrogen molecules per cationcharge as a function of pressure for LiX KX and CaX at 100K

with increasing pressure at low pressure (less than 1MPa)whereafter it increases slowly at high pressure (above 4MPa)The hydrogen adsorption capacity of the zeolites at anygiven pressure decreases in the order of CaX gt LiX gt KXand basically keeps the same order at all temperatures Thehighest hydrogen adsorption capacity at 100K and 10MPawas obtained on zeolite CaX and calculated to be 231 wtthrough convertingmmolg value in Figure 1 to facilitate sub-sequent comparison with the literature data The hydrogenadsorption capacities reported for LiX KX and CaX zeolitesat above 100K were very scarce in the literatures Li and Yang[13] and Wang and Yang [32] reported that the hydrogenstorage capacities on Li+ Ca2+ and Mg2+ ion-exchanged Xtype zeolites at 298K and 10MPa were 3wt 05 wt and027wt respectively In this work the calculated valuesof hydrogen storage capacity at 293K and 10MPa for LiXand CaX zeolites are 03 wt and 076wt respectively ascan be seen in Figure 1 There are two possible reasons forthe aforementioned difference Firstly the unit cell structuresused in simulation studies are perfect crystalline Howeverthe experimentally used Li+ K+ and Ca2+ cation exchangedzeolite samples are not always perfect crystalline Cationexchange may result in partial breaking of the cages with thesmaller window diameter such as 120573-cage with six-memberring (about 26 oplus) The hydrogen molecules can enter thecagesThis could be themain reason for observance of higherhydrogen adsorption capacity from experimental results ascompared with simulation calculations However prepara-tion of such a sample is not practically feasible as zeolitesamples lose crystallinity on cation exchange Secondly weused force field based simulation for the adsorption isothermgeneration in which nonbonded interactions like van derWaals and coulombic interactions were considered Howeverdifferent parameterizations of the LJ potentials for the Al SiO and metal cations of the zeolite X have been proposedin the literature on a theoretical basis for instance in

LiX

KXCaX

4

45

5

55

0 02 04 06 08

6

Adsorbed capacity (mmolmiddotgminus1)

Isos

teric

hea

t of a

dsor

ptio

n (k

Jmol

minus1)

Figure 3 Relationship between isosteric heat of adsorption andadsorbed hydrogen on zeolites LiX KX and CaX

[23 24 33] They were used in simulation of gas adsorptionand sometimes were modified in order to achieve a betteragreement between simulation and experimental results Inour simulations the estimation of LJ parameters used forthe simulation of hydrogen adsorption in the Li+ K+ andCa2+ exchanged zeolites also has influence on the calculatedhydrogen adsorption capacity

In order to investigate the effect of cation exchange on thehydrogen adsorption the curves of the number of hydrogenmolecules per cation charge versus pressure at 100K for Li+K+ and Ca2+ exchanged X zeolites were simulated as shownin Figure 2 The profile of these curves is similar to thatof the corresponding hydrogen adsorption isotherms shownin Figure 1 In the pressure range from 0 to 0785MPa thenumber of hydrogen molecules per cation charge followsthe order LiX gt CaX gt KX whereas the order changesto CaX gt LiX gt KX in the pressure range from 0785 to10MPa As a result a ldquocrossoverrdquo of the hydrogen adsorptionisotherm curves for CaX and LiX zeolites appears This trendof hydrogen adsorption in these zeolites may be explainedby Franekelrsquos [34] earlier observations and postulation thathydrogen uptake in zeolites was related to the availablevoid volume per gram of zeolite which decreases withincreasing size and number of the exchangeable cations TheKX containing larger alkali-metal K+ cations has the samenumber of exchangeable cations as that of LiX but occupya substantially bigger space with a consequent reduction invoid volume available for hydrogen adsorption Howeverwhen Na+ cations in NaX are replaced by alkaline-earthmetal divalent cations (ie Ca2+) the number of cations inzeolite decreases thus the available void volume increasesaccordingly Hydrogen uptake had previously been shownto be related to the micropore volume in zeolites [7] Theavailable void volume is related to the number and size ofexchangeable cations [34] In general zeolites containingalkali-metal and alkaline-earth metal cations have a large


0

01

02

03

04

05

minus8 minus6 minus4 minus2 0

Poiss

on d

istrib

utio

n of

ener

gy

001 MPa01 MPa05 MPa

5 MPa10 MPa

Energy(kJmiddotmolminus1)

(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy

minus6 minus4 minus2 0

001 MPa01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


001 MPa01 MPa05 MPa

5 MPa10 MPa


(c)Figure 4 Distribution of hydrogen adsorption energy of hydrogen for (a) LiX (b) KX and (c) CaX at 100K at different pressures

number of exchangeable cations which occupy a substantialvolume with a consequent reduction in the space availablefor hydrogen uptake Maurin et al [35] reported that themicropore volumes of Li+ K+ andCa2+ exchangedX (SiAl =10) zeolites were 0272 0204 and 0324mLsdotgminus1 respectivelyby using nitrogen adsorption at 77K This may explainthat larger and more cations may limit the available voidvolume by occupying more space themselves which resultsin the lower hydrogen uptake However in a more confinedsystem adsorption may cause variation of the available voidvolume (due to varying sizes of pores) At low pressurethe adsorption is stronger due to the enhanced interactionof hydrogen molecules with the pore walls for the smallerpores such as LiX and KX zeolites in this work Howeverthe pore volumes are small for LiX and KX zeolites As the

adsorbed amount increases the ldquosmallerrdquo pores are moreeasily saturated or blocked Thus the amount adsorbed insmall pores is lower at higher pressure This usually createsa ldquocrossoverrdquo of adsorption isotherm curves for pores ofvarying sizes

We have also calculated the isosteric heat of adsorption byusing the Clausius-Clapeyron equation from the isotherms atvarious temperatures (the hydrogen adsorption capacity is inthe range of 002ndash07mmolsdotgminus1 at low pressure range below1MPa see Figure 1) Figure 3 illustrates the relationshipbetween the isosteric heat of adsorption and the hydrogenadsorption capacityThe isosteric heats of adsorption of thesezeolites are around 4ndash6 kJsdotmolminus1 indicating physisorptionmechanism As shown in Figure 3 the influence of isostericheat of adsorption on the hydrogen uptake values is similar


(a) (b)

(c) (d)

(e) (f)

Figure 5 Mass cloud of H2in (a) LiX at 01MPa (b) LiX at 10MPa (c) KX at 01MPa (d) KX at 10MPa (e) CaX at 01MPa and (f) CaX at

10MPa performed at 100K

for the three zeolites Weinberger et al [33] reported thatthe average heats of adsorption varied between 55 kJsdotmolminus1and 75 kJsdotmolminus1 for the Li-LSX zeolites with different ratioof cation exchange Li et al [36] reported that the isostericheats of adsorption for hydrogen on Zn2+ and Ni2+ cationsexchanged X zeolites were 36ndash50 kJsdotmolminus1 Moreover forparent materials NaX the isosteric heat of adsorption forhydrogen was in the range of 35ndash70 kJsdotmolminus1 [37ndash39] Thisindicates that our calculated results are in good agreementwith the experimental results reported in the literature

As also shown in Figure 3 the isosteric heats of adsorp-tion on all the three zeolites decrease appreciably with theincrease in hydrogen adsorption capacity This could beattributed to the energetic heterogeneities of the adsorbents

[40] For heterogeneous surfaces in the micropores of someadsorbents such as CMS and activated carbon verticalinteractions between the solid surface molecules and gasmolecules decrease as the adsorption capacity increases [41]TheX andA types of zeolites are energetically heterogeneouswhich could be caused by nonuniform distribution of silica-alumina in the framework location and distribution ofone or more cations of different charge densities in theframework and presence of trace water in the cages andso forth [40] Moreover the isosteric heat of adsorption forthe three zeolites follows the order of LiX gt CaX gt KXat the same adsorbed amount (for 002ndash07mmolsdotgminus1 iefor lower pressure range) Since isosteric heat of adsorptionindicates the strength of adsorberadsorbent interactions


0

01

02

03

04

05

minus7 minus6 minus5 minus4 minus3 minus2 minus1 0

Poiss

on d

istrib

utio

n of

ener

gy

01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy

minus6 minus5 minus4 minus3 minus2 minus1 0

01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(c)

Figure 6 Distribution of hydrogen adsorption energy for (a) LiX (b) KX and (c) CaX at 293K at different pressures

it is illustrated that the interaction between hydrogen andzeolites pore wells (or cations) is in the order of LiX gt CaXgt KX at low pressure implying that the smaller cations areable to produce a stronger electrostatic field to polarize thesymmetric hydrogen molecules

Figure 4 illustrated the distribution of hydrogen adsorp-tion energy at 100K and pressures 119875 = 001 01 05 5 and10MPa for LiX KX andCaX zeolites For a given zeolite onlyone main binding energy peak was observed and its centershifted from the high energy position to low energy positionby increasing pressure It is indicated that there are also twotypes of adsorption sites for hydrogen adsorption inX zeolitesand the effect of the pressure (loading) on adsorption energybecomes important at 100K At low pressure hydrogenmolecules are adsorbed preferentially on the higher bindingenergy sites such as the site II and III cations and the oxygen

atoms of the framework and these sites are relatively morequickly saturated than the lower binding energy sites suchas preadsorbed hydrogen and the inner pores of zeolite awayfrom the surface These were confirmed by the observationof the mass density plots as shown in Figure 5 As thepressure increases hydrogen molecules gradually cover thelower binding sites around preadsorbed hydrogen and theinner pores of zeolite away from the surface Eckert et al[42] revealed that hydrogen adsorption sites in NaX zeolitewere distributed near site II and III cations determined bythe inelastic neutron scattering (INS) technology Kazanskyet al [14 15] also confirmed that the adsorption sites ofhydrogen on ion-exchanged X and Y zeolites were mainlyat site II and III cations inside supercages of the zeoliteframework and the adjacent basic oxygen anions by usingDRIFT spectra method For the temperatures of 140K and


(a) (b)

(c)

Figure 7 Mass cloud of H2in (a) LiX (b) KX and (c) CaX at 293K and 10MPa

195 K the distribution of hydrogen adsorption energy atpressures 119875 = 001 01 05 5 and 10MPa for LiX KX andCaX zeolites follows the same trend as that at 100K

Figure 6 shows the distribution of hydrogen adsorptionenergy for LiX KX and CaX zeolites at 293K At 293K onemain binding energy peak was observed for these zeolitessame as the situation at 100K However the positions of thesebinding energy peaks are not affected by the pressure It seemsthat the high binding energy sites (the extraframework metalcations) become less effective to firmly hold the hydrogenmolecules at higher temperature And the oxygen atomsof zeolite framework are the stable adsorption sites Thisphenomenon was confirmed by the analysis of mass densitydistribution at 293K as shown in Figure 7 The increasedtemperature induces hydrogen molecules to be distributedmore broadly at weak interaction sites due to the increasedkinetic energy Prasanth et al [43] found that the physicaladsorption of the cations in RhX and NiX zeolites to H

2

is negligible at 303 and 333K and the observed hydro-gen adsorption is due to the chemisorption on nickel andrhodiummetals For the temperatures of 230K and 260K thedistribution of hydrogen adsorption energy at pressures 119875 =01 05 5 and 10MPa for LiX KX and CaX zeolites followsthe same trend as that at 293K

4 Conclusions

Our simulation results based onGCMCmethod at 100ndash293Kand pressures up to 10MPa reveal that Li+ K+ and Ca2+

exchanged X zeolites are promising materials for hydrogenstorage The hydrogen adsorption is affected mainly by thetype of cations exchanged in the framework structure at thesame temperature and pressure Ca2+ exchanged X zeoliteexhibited the higher hydrogen adsorption capacity than thoseof Li+ and K+ exchanged X zeolites This can be attributedto the larger available micropore volume fewer Ca2+ andsmaller cation radius of Ca2+ for CaX zeolite Upon furtheranalysis of the simulation results we believe that the siteII and III cations and oxygen atoms of the framework arethe main adsorption sites of hydrogen molecules at lowertemperature whereas the stable adsorption sites are onlyoxygen atoms of zeolites framework at higher temperatureTherefore elevation of adsorption energy and increase ofstable adsorption sites are the main future aspects for thedesign of new hydrogen storage materials by introducing thenew extraframework metal cations into zeolites

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial supportfrom the program for Liaoning Excellent Talents in Univer-sity (LNET) China (LJQ2012016)


References

[1] L Schlspbach and A Zttel ldquoReview article Hydrogen-storagematerials for mobile applicationsrdquoNature vol 414 pp 353ndash3582001

[2] L Schlapbach ldquoHydrogen as a fuel and its storage for mobilityand transportrdquoMRS Bulletin vol 27 no 9 pp 675ndash676 2002

[3] S M Aceves G D Berry and G D Rambach ldquoInsulatedpressure vessels for hydrogen storage on vehiclesrdquo InternationalJournal of Hydrogen Energy vol 23 no 7 pp 583ndash591 1998

[4] A Dedieu Transitional Metal Hydrides Wiley-VCH New YorkNY USA 1992

[5] F Lamari Darkrim P Malbrunot and G P Tartaglia ldquoReviewof hydrogen storage by adsorption in carbon nanotubesrdquoInternational Journal of Hydrogen Energy vol 27 no 2 pp 193ndash202 2002

[6] HW Langmi AWalton M M Al-Mamouri et al ldquoHydrogenadsorption in zeolites A X Y and RHOrdquo Journal of Alloys andCompounds vol 356-357 pp 710ndash715 2003

[7] M G Nijkamp J E M J Raaymakers A J van Dillen andK P de Jong ldquoHydrogen storage using physisorption-materialsdemandsrdquo Applied Physics A vol 72 no 5 pp 619ndash623 2001

[8] N L Rosi J Eckert M Eddaoudi et al ldquoHydrogen storage inmicroporous metal-organic frameworksrdquo Science vol 300 no5622 pp 1127ndash1129 2003

[9] L Regli A Zecchina J G Vitillo et al ldquoHydrogen storagein Chabazite zeolite frameworksrdquo Physical Chemistry ChemicalPhysics vol 7 no 17 pp 3197ndash3203 2005

[10] F Stephanie-Victoire A-M Goulay and E Cohen de LaraldquoAdsorption and coadsorption of molecular hydrogen isotopesin zeolites 1 Isotherms of H2 HD and D2 in NaA by thermo-microgravimetryrdquo Langmuir vol 14 no 25 pp 7255ndash72591998

[11] M A Makarova V L Zholobenko K M Al-Ghefaili N EThompson J Dewing and J Dwyer ldquoBroslashnsted acid sites inzeolites FTIR study ofmolecular hydrogen as a probe for aciditytestingrdquo Journal of the Chemical Society Faraday Transactionsvol 90 no 7 pp 1047ndash1054 1994

[12] A Zecchina S Bordiga J G Vitillo et al ldquoLiquid hydrogen inprotonic chabaziterdquo Journal of the American Chemical Societyvol 127 no 17 pp 6361ndash6366 2005

[13] Y Li and R T Yang ldquoHydrogen storage in low silica type Xzeolitesrdquo Journal of Physical Chemistry B vol 110 no 34 pp17175ndash17181 2006

[14] V B Kazansky V Y Borovkov A Serich andH G Karge ldquoLowtemperature hydrogen adsorption on sodium forms of fauja-sites barometric measurements and drift spectrardquoMicroporousand Mesoporous Materials vol 22 no 1ndash3 pp 251ndash259 1998

[15] V B Kazansky ldquoDrift spectra of adsorbed dihydrogen as amolecular probe for alkaline metal ions in faujasitesrdquo Journalof Molecular Catalysis A vol 141 pp 83ndash94 1999

[16] M Feuerstein and R F Lobo ldquoCharacterization of Li cationsin zeolite LiX by solid-state NMR spectroscopy and neutrondiffractionrdquoChemistry ofMaterials vol 10 no 8 pp 2197ndash22041998

[17] K Seff and L Zhu ldquoCation crowding in zeolites reinvestigationof the crystal structure of dehydrated potassium-exchangedzeolite Xrdquo Journal of Physical Chemistry B vol 104 no 38 pp8946ndash8951 2000

[18] Y I Smolin Y F Shepelev and A A Anderson ldquoAtomic scalemechanism of CaX zeolite dehydrationrdquo Acta CrystallographicaB vol 45 pp 124ndash128 1989

[19] DW Lewis A R Ruiz-Salvador A Gomez et al ldquoZeolitic imi-dazole frameworks structural and energetics trends comparedwith their zeolite analoguesrdquo CrystEngComm vol 11 no 11 pp2272ndash2276 2009

[20] httpwwwpwscforg[21] J R Hill and J Sauer ldquoMolecular mechanics potential for silica

and zeolite catalysts based on ab initio calculations 1 Dense andmicroporous silicardquo Journal of Physical Chemistry vol 98 no 4pp 1238ndash1244 1994

[22] A Michels W de Graaff and C A Ten Seldam ldquoVirial coef-ficients of hydrogen and deuterium at temperatures between -175∘C and +150∘C Conclusions from the second virial coeffi-cient with regards to the intermolecular potentialrdquo Physica vol26 no 6 pp 393ndash408 1960

[23] K Watanabe N Austin and M R Stapleton ldquoInvestigation ofthe air separation properties of zeolites types A X and Y bymonte carlo simulationsrdquo Molecular Simulations vol 15 no 4pp 197ndash221 1995

[24] E Beerdsen D Dubbeldam B Smit T J H Vlugt and SCalero ldquoSimulating the effect of nonframework cations on theadsorption of alkanes in MFI-type zeolitesrdquo Journal of PhysicalChemistry B vol 107 no 44 pp 12088ndash12096 2003

[25] L Uytterhoeven D Dompas and W J Mortier ldquoTheoreticalinvestigations on the interaction of benzene with faujasiterdquoJournal of the Chemical Society Faraday Transactions vol 88no 18 pp 2753ndash2760 1992

[26] M P Allen andD J Tildesley Simulation of Liquids ClarendonOxford UK 1987

[27] Y P Joshi and D J Tildesley ldquoMolecular dynamics simulationand energyminimization of O

2adsorbed on a graphite surfacerdquo

Surface Science vol 166 no 1 pp 169ndash182 1986[28] B Weinberger F D Lamari S B Kayiran A Gicquel and D

Levesque ldquoMolecular modeling of H2 purification on Na-LSXzeolite and experimental validationrdquo AIChE Journal vol 51 no1 pp 142ndash148 2005

[29] A Gupta S Chempath M J Sanborn L A Clark and R QSnurr ldquoObject-oriented programming paradigms formolecularmodelingrdquoMolecular Simulation vol 29 no 1 pp 29ndash46 2003

[30] A V Kumar H Jobic and S K Bhatia ldquoQuantum effectson adsorption and diffusion of hydrogen and deuterium inmicroporous materialsrdquo Journal of Physical Chemistry B vol110 no 33 pp 16666ndash166671 2006

[31] A W C van den Berg S T Bromley J C Wojdel and J CJansen ldquoAdsorption isotherms of H

2in microporous materials

with the SOD structure a grand canonical Monte Carlo studyrdquoMicroporous and Mesoporous Materials vol 87 no 3 pp 235ndash242 2006

[32] L F Wang and R T Yang ldquoHydrogen storage properties oflow-silica type X zeolitesrdquo Industrial and Engineering ChemistryResearch vol 49 pp 3634ndash3641 2010

[33] B Weinberger F D Lamari A Veziroglu S Beyaz and MBeauverger ldquoAccurate gas zeolite interaction measurementsby using high pressure gravimetric volumetric adsorptionmethodrdquo International Journal of Hydrogen Energy vol 34 no7 pp 3191ndash3196 2009

[34] B D Franekel ldquoZeolitic encapsulation Part 2 percolationand trapping of inert gases in A-type zeolitesrdquo Journal of theChemical Society Faraday Transactions I vol 77 pp 2041ndash20521981

[35] G Maurin P L Llewellyn T Poyet and B Kuchta ldquoAdsorp-tion of argon and nitrogen in X-faujasites relationships for


understanding the interactions with monovalent and divalentcationsrdquoMicroporous and Mesoporous Materials vol 79 no 1ndash3 pp 53ndash59 2005

[36] J Li E Wu J Song F Xiao and C Geng ldquoCryoadsorptionof hydrogen on divalent cation-exchanged X-zeolitesrdquo Interna-tional Journal of Hydrogen Energy vol 34 no 13 pp 5458ndash54652009

[37] XM Du and E DWu ldquoPhysisorption of hydrogen in A X andZSM-5 types of zeolites at moderately high pressuresrdquo ChineseJournal of Chemical Physics vol 19 pp 457ndash462 2006

[38] R Yamk U Yamk C Heiden and J G Daunt ldquoAdsorptionisotherms and heats of adsorption of neon and hydrogen onzeolite and charcoal between 20 and 90 Krdquo Journal of LowTemperature Physics vol 45 no 5-6 pp 443ndash455 1981

[39] M A Levin A A Fomkin A A Isirikyan and V V SerpinskiildquoAdsorption heats of hydrogen isotopes on zeolite Nax atelevated pressuresrdquo Bulletin of the Academy of Sciences of theUSSR Division of Chemical Science vol 35 no 12 p 2594 1986

[40] T C Golden and S Sircar ldquoGas adsorption on silicaliterdquo Journalof Colloid And Interface Science vol 162 no 1 pp 182ndash188 1994

[41] Y D Chen R T Yang and P Uawithya ldquoDiffusion of oxygennitrogen and their mixtures in carbon molecular sieverdquo AIChEJournal vol 40 no 4 pp 577ndash585 1994

[42] J Eckert F R Trouw and M McMenomy ldquoCo-adsorptionstudies of hydrogen with nitrogen in zeolitesrdquo in Proceedings ofthe Workshop Materials Research Using Cold Neutrons at PulsedNeutron Sources August 1997

[43] K P Prasanth R S Pillai H C Bajaj et al ldquoAdsorptionof hydrogen in nickel and rhodium exchanged zeolite XrdquoInternational Journal of Hydrogen Energy vol 33 no 2 pp 735ndash745 2008

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



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Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


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MaterialsJournal of


Nano

materials


Journal ofNanomaterials


100ndash293K and the pressures up to 10MPa by using GrandCanonical Monte Carlo (GCMC) method The dependenceof the hydrogen adsorption capacity of zeolites on tempera-ture pressure cation type adsorption site distribution andadsorption potential energy was discussed

2 Computational Details

Structures of the initial unit cell of alkali-metal and alkali-earth metal cations (Li+ K+ Ca2+) exchanged X zeolites suchas LiX KX and CaX (X = Si

96Al96O384

SiAl = 10) wereconstructed according to the results of X-ray crystallographicstudies [16ndash18] The crystal is cubic with unit cell parameters119886 = 25099 A and space group Fd-3 In dehydrated LiXzeolite there are three Li+ cation sites 32 Li+ cations arelocated in site I1015840 (in the120573-cage close to the hexagonal windowto the hexagonal prism) site II (in the six-member ring ofthe 120573-cage) and site III (in the supercage close to a squarewindow between two other square windows) respectivelyIn dehydrated KX zeolite there are four K+ cation sitesThe occupancies of these K+ cations at cation sites I (in thehexagonal prism) I1015840 II and III in zeolite KX are 16 16 32and 32 respectively For the dehydrated CaX zeolite the Ca2+cations are located in site I (12 Ca2+ cations) site I1015840 (4 Ca2+cations) and site II (32 Ca2+ cations) After constructingthe initial structure we performed energy minimizationcalculations to determine the equilibrium structures usingdensity function theory (DFT) method that was successfullyused to explore hypothetical FAU with dense topologies [19]DFT calculations were carried out with the code Quantum-ESPRESSO [20] which uses atom centered basis functionsthat are particularly efficient for total energy studies of verylow density materials with very large unit cells PeriodicDFT calculations were carried out using the PBE exchangecorrelation functional within the GGA approximation Thezeolites with minimized energy were used as adsorbents forhydrogen adsorption

For hydrogen adsorption on LiX KX and CaX zeolitesthe force field used was an enhanced version of the polymerconsistent force field (PCFF) [21] Because the host of X zeo-lite was treated as a rigid structure with fixed atom positionsobtained from theminimized structure at all simulations thetotal energy of the zeolite framework and adsorbedmolecules(119864total) is expressed as the sum of the short-range van derWaals (vdW) nonbond interaction energy (119864vdW) and thelong-range coulombic interaction energy (119864c)

119864total = 119864vdW + 119864c (1)

The vdW interactions between hydrogen and the zeoliteframework atoms are represented by Lennard-Jones (LJ)potential with the following expression

119864vdW = sum119894

sum

119895gt119894

(4120576119894119895[(

120590119894119895

119903119894119895

)

12

minus (

120590119894119895

119903119894119895

)

6

]) (2)

where 120576119894119895and 120590

119894119895are the LJ potential parameters that were

obtained from 120576119894and 120590

119894of each species by using the Lorentz

Berthelotmixing rule (ie a geometric combining rule for the

Table 1 Lennard-Jones parameters used for hydrogen adsorptionon ion-exchanged X zeolite

Atom type 120576 (kcalmol) 120590 (oplus) ReferenceH 00726 2958 [22]Si 00370 0076 [23]Al 00384 1140 [23]O 03342 3040 [23]Li 00249 2180 [24]K 00356 3020 [24]Ca 01553 2980 [24]

energy and an arithmetic one for the atomic size 120576119894119895= radic120576119894 sdot 120576119895

and 120590119894119895= (120590119894+ 120590119895)2) 119903

119894119895is the interatomic distance between

the 119894th and 119895th atomsThe LJ potential parameters used in allsimulations were summarized in Table 1

The coulombic electrostatic interaction energy is thelong-range interaction and the model systems are periodicSo Ewald sum was used for 119864c

119864c = sum119894

sum

119895gt119894

119902119894119902119895

119903119894119895

(3)

where 119902119894and 119902119895are the net atomic charges of the 119894th and 119895th

atoms respectivelyFor the assignment of charges of extraframework cations

Li+ K+ and Ca2+ and framework atoms Si Al and O thevalues of charges were obtained by using the electronegativityequalization method (EEM) which are taken from theliterature as given in Table 2 [25]

For hydrogen we used three-point charge model [23 2627] where the two outer sites are separated by a distance of119897 = 07414 A having a charge of 119902 = minus021119890 [28] and the thirdmidpoint has a point charge of minus2119902

All GCMC simulations were performed by employingthe Multipurpose Simulation Code (MUSIC) [29] The load-ing at a constant pressure and temperature was calculatedby attempting with equal probability to insert delete ortranslate one H

2molecule in the simulation cell Trial moves

considered here were the translation insertion and deletionof particles [30 31] The moves for each run were randomlychosen with equal probability The random movements ofmolecules make new configurations which may be acceptedaccording to Metropolisrsquos sampling scheme Each structuremodel consists of one elementary cell with three-dimensionalperiodic boundary conditionsThe cut-off distance for short-range LJ summation was set to 12 oplus which is less than halfof the length of the simulation box (25099 A) and the half ofthe cell length for Ewald summation was used The numberof GCMC steps was set to 2 times 107 for each simulation Thenumber of trial moves in an MC cycle is equal to the numberof adsorbed molecules Usually approximately 15 of thecycles were performed for equilibration and the subsequentcycles were used for statistics The simulation temperaturesincluded 6 temperatures 100K 140K 195 K 230K 260Kand 293K





0

2

4

6

8

10

Pressure (MPa)

H2

adso

rptio

n (m

molmiddotgminus1)

0 2 4 6 8 10 12 14

100 K140 K195 K

230 K260 K293 K

(a)

0

2

4

6

8

H2

adso

rptio

n (m

molmiddotgminus1)

100 K 230 K260 K293 K

Pressure (MPa)0 2 4 6 8 10 12 14

140 K195 K

(b)

0

2

4

6

8

10

12

14

H2

adso

rptio

n (m

molmiddotgminus1)

100 K 230 K260 K293 K

Pressure (MPa)0 2 4 6 8 10 12 14

140 K195 K






0

03

06

09

12

15

Pressure (MPa)

LiXKXCaX

H2

mol

ecul

esc

harg

e

0 2 4 6 8 10 12



LiX

KXCaX

4

45

5

55

0 02 04 06 08

6


Isos

teric

hea

t of a

dsor

ptio

n (k

Jmol

minus1)





0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

001 MPa01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


001 MPa01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


001 MPa01 MPa05 MPa

5 MPa10 MPa







(a) (b)

(c) (d)

(e) (f)







0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(c)






(a) (b)

(c)




2


4 Conclusions





Acknowledgment



References

























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







0

2

4

6

8

10

Pressure (MPa)

H2

adso

rptio

n (m

molmiddotgminus1)

0 2 4 6 8 10 12 14

100 K140 K195 K

230 K260 K293 K

(a)

0

2

4

6

8

H2

adso

rptio

n (m

molmiddotgminus1)

100 K 230 K260 K293 K

Pressure (MPa)0 2 4 6 8 10 12 14

140 K195 K

(b)

0

2

4

6

8

10

12

14

H2

adso

rptio

n (m

molmiddotgminus1)

100 K 230 K260 K293 K

Pressure (MPa)0 2 4 6 8 10 12 14

140 K195 K






0

03

06

09

12

15

Pressure (MPa)

LiXKXCaX

H2

mol

ecul

esc

harg

e

0 2 4 6 8 10 12



LiX

KXCaX

4

45

5

55

0 02 04 06 08

6


Isos

teric

hea

t of a

dsor

ptio

n (k

Jmol

minus1)





0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

001 MPa01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


001 MPa01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


001 MPa01 MPa05 MPa

5 MPa10 MPa







(a) (b)

(c) (d)

(e) (f)







0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(c)






(a) (b)

(c)




2


4 Conclusions





Acknowledgment



References

























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

03

06

09

12

15

Pressure (MPa)

LiXKXCaX

H2

mol

ecul

esc

harg

e

0 2 4 6 8 10 12



LiX

KXCaX

4

45

5

55

0 02 04 06 08

6


Isos

teric

hea

t of a

dsor

ptio

n (k

Jmol

minus1)





0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

001 MPa01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


001 MPa01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


001 MPa01 MPa05 MPa

5 MPa10 MPa







(a) (b)

(c) (d)

(e) (f)







0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(c)






(a) (b)

(c)




2


4 Conclusions





Acknowledgment



References

























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

001 MPa01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


001 MPa01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


001 MPa01 MPa05 MPa

5 MPa10 MPa







(a) (b)

(c) (d)

(e) (f)







0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(c)






(a) (b)

(c)




2


4 Conclusions





Acknowledgment



References

























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)

(e) (f)







0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(c)






(a) (b)

(c)




2


4 Conclusions





Acknowledgment



References

























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

01

02

03

04

05


Poiss

on d

istrib

utio

n of

ener

gy

01 MPa05 MPa

5 MPa10 MPa


(a)

0

01

02

03

04

05

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(b)

0

005

010

015

020

Poiss

on d

istrib

utio

n of

ener

gy


01 MPa05 MPa

5 MPa10 MPa


(c)






(a) (b)

(c)




2


4 Conclusions





Acknowledgment



References

























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c)




2


4 Conclusions





Acknowledgment



References

























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




References

























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article molecular simulation of hydrogen storage...

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