Guest–host encapsulation of microporous zeolites in ordered

mesoporous materials by molecular simulations

C. G. Sonwane* and Q. Li

School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 FerstDr., Atlanta, GA 30332, USA. E-mail: shekar@nanoporous.com; Fax: 1-859-406-3838;Tel: 1-763-234-5738

Received 8th June 2005, Accepted 29th July 2005First published as an Advance Article on the web 18th August 2005

The present work provides the first study of ordered mesoporous materials SBA-15 coated with microporouszeolites ZSM-5 using molecular simulations. Several model structures with characteristics such as periodicarrangement of mesopores, randomly arranged micropores, surface hydroxyls and bulk deformations of SBA-15were used. Cartesian coordinates of ZSM-5 unit lattice were obtained from the literature and the 100 face of H-ZSM-5 unit cell was then placed on the surface of SBA-15 and the entire structure was equilibrated to obtainfinal configuration. The resulting structure was characterized using simulated small angle and wide angle X-raydiffraction, Connolly surface area (to compare BET area), accessible pore volume for nitrogen molecules (tocompare with t-plot volume of micro and mesopores) and methane adsorption at 303 K. The orientation ofZSM-5 on the SBA-15 had no effect on the surface area, pore volume or adsorption capacity. In order to findout if the addition of microporous ZSM-5 should increase the total methane adsorption capacity due to additionof micropores, we studied adsorption on bare and coated SBA-15. However, total adsorption capacity was foundto decrease, while the number of methane molecules adsorbed per unit cell of the SBA-15 structure increased. Anexisting experimental method (J. Am. Chem. Soc., 2004, 126, 14324) of the synthesizing hybrid ZSM-5/SBA-15structure was studied using accessible micropore volume (by t-plot). It was found that the procedure made all themicropores inaccessible. A modification of the method or use of other host materials is suggested to use thebenefits of narrow micropore distribution in ZSM-5.

1. Introduction

Mesoporous molecular sieves such as MCM-412 and SBA-153

have been widely studied because of their unique periodicstructures consisting of uniform size mesopores arranged ona 2-D lattice. It is believed that the walls of MCM-41 arerough,4,5 but no networking exists in the walls joining themesopore channels.6–9 However, SBA-15 which has porestructure similar to MCM-41, consists of mesopore channelsconnected through micro and mesopores in the walls.10–16 Thepore size and wall thickness of SBA-15 is relatively larger thanMCM-41. The size and total volume of these micropores in thewalls of SBA-15 can be adjusted by modifying the synthesisconditions.10–12 These materials have a high specific surfacearea (ca. 1000 m2 g�1 for MCM-41 and ca. 800 m2 g�1 forSBA-15) and a large pore volume measured by nitrogenadsorption isotherms.

SBA-15 has been widely used as a catalyst support17,18 andmore recently, in a diverse array of other applications. Some oftheir recent applications include use as adsorbents for removalof volatile organic compounds and toxic gases or as chemicalsensors,15,19–21 as a host and carrier for antibiotics like amoxi-cillin in pharmaceutical applications,22 in separation of lighthydrocarbons23 or size selective separation of proteins,24 as ahost for biosensors,25 for separation of CO2,

26 for catalyticconversion of fatty acids to gasoline27 and in fabrication ofmembranes.28 The pore structure of SBA-15 materials can alsobe used as a template for the synthesis of a family of carbon-based ordered nanoporous CMK materials.29 The ultra-highsurface area associated with these CMK materials makes thempotential candidates for other applications including hydrogenstorage and batteries.

1.1 Coating of SBA-15 by ZSM-5

Recently, there have been attempts to either coat the walls ofthese SBA-15 materials with zeolites by post-synthetic treat-ment1,30,31 or make the walls of the SBA-15 from a zeoliteusing CMK-3 as a template.32 Meynen et al.30 deposited V-zeolite nanoparticles in SBA-15 using post-synthetic treatment.They found that the final material has a higher microporosity(ca. 0.17 cm2 g�1) than the original SBA-15 (ca. 0.11 cm2 g�1).In their results, although the trend of increase in microporosityis according to the expectations and probably correct, theabsolute value of micropore volumes may not be accurate.This is because of the traditional debate in applying the t-plotor alpha-plot methods. They also found that such a methodgives rise to greater crystallinity of the SBA-15 walls. Doet al.1,31 found that the coating of SBA-15 with ZSM-5 reducesthe average diameter of SBA-15 from 7 to 5.4 nm, the surfacearea from 800 to 465 m2 g�1, and the pore volume from 1.56 to0.78 cm3 g�1. After the t-plot analysis of their nitrogenisotherm indicated that the coated sample had negligiblemicropores (as shown in Fig. 1), the total micropore volumeof the uncoated SBA-15 sample was found to be ca. 0.05 cm2

g�1(ca. 5% of total pore volume). The coated sample hadnegligible micropores as shown in Fig. 1, which means that oncoating the SBA-15 with ZSM-5, the micropores in the walls ofSBA-15 as well as in ZSM-5 will be all blocked.The results lead one to conclude that such a method of

coating1 merely strengthens or changes other aspects of thewalls without increasing microporosity due to ZSM-5. Asignificant change in the synthesis method is needed in orderto use the full benefit of possible uniform size bimodal ma-terials. Sakthivel et al.32 synthesized replicated mesoporous

R E S E A R C H P A P E R

PC

CP

ww

w.rsc.o

rg/p

ccp

DO

I:1

0.1

03

9/b

50

81

02

e

P h y s . C h e m . C h e m . P h y s . , 2 0 0 5 , 7 , 3 5 0 1 – 3 5 0 6 3501T h i s j o u r n a l i s & T h e O w n e r S o c i e t i e s 2 0 0 5

Publ

ishe

d on

18

Aug

ust 2

005.

Dow

nloa

ded

by U

nive

rsity

of

Nor

th C

arol

ina

at C

hape

l Hill

on

29/1

0/20

14 1

5:17

:34.

View Article Online / Journal Homepage / Table of Contents for this issue

materials (RMM) having hexagonally ordered mesopores si-milar to SBA-15 but the walls were made up of ZSM-5. Theyfound that the RMM’s contain 0.08 cm2 g�1 micropores (about10% of the total pore volume). Also, it was reported that theRMM’s have superior thermal, hydrothermal, mechanicalstability and improved acidic properties. These studies indicatethat the synthesis of new kinds of porous materials withbimodal distribution having a narrow range of both micro-pores and mesopores is possible.

1.2 Brief literature review of computational studies of

ordered mesoporous materials

The models studying the structure and properties of orderedmesoporous aluminosilicate materials in the literature can bebroadly classified in three main categories. A comprehensivereview of models is provided in our earlier manuscript.50 Abrief part of that review is provided here for completeness.

(i) Smooth tube or cylinder. Seaton and coworkers33,34 used aseries of models based on cylindrical tubes. The arrangement ofsilicon and oxygen atoms was either quartz or random follow-ing certain bonding rules. The models were found to besuccessful in predicting adsorption of hydrocarbons. Kuchtaand co-workers,35 modeled MCM-41 as an array of oxygenatoms in a cylindrical annulus. Cao and co-workers,36 used asmooth cylindrical pore to represent the MCM-41. UsingGCMC and the density functional theory (DFT) they founda good comparison between the simulation and experimentsfor the adsorption isotherm of nitrogen at 77 K, as well ascarbon tetrachloride and methane at 273 K. The earliest workof Neimark and co-workers,37 used non-local density func-tional theory to study the adsorption and capillary condensa-tion of gases in MCM-41. The work was followed up with 2-DNLDFT by Do et al.38 The MCM-41 was modeled as a smoothinfinite cylindrical pore by both of these research groups.

(ii) Models with density variation in the walls by fitting SAXS

data. White and co-workers39 based on SAXS data, developeda model in which the walls are made up of two layers withdifference in densities. Using White and co-workers approach,Solovyov et al.40 suggested that the walls of the MCM-41 arenot continuous and smooth and there is a possibility of gaps/holes in the walls.

(iii) Hexagonal or cubical arrangement of mesopores (with no

micropores in the wall). Feutson and Higgins41 used classicalmolecular dynamics to study MCM-41 materials of a series oflattice constants and wall thicknesses. They found an excellentagreement between the experiments and simulations for MCM-41 with walls thicker than 1.1 nm. Koh and co-workers42

developed a model which involves insertion of Si and oxygenatoms randomly inside a unit cell of the size determined byXRD until the correct wall density is obtained. They havefound that the simulated values of selectivity for CH2Cl2 aresignificantly higher than the experimental results. Schacht andco-workers,43 in order to assess the significance of XRD andTEM images, constructed computer models of amorphoussilica with a 1-D pore system and hexagonally arranged pores.They found that the simulated TEM images obtaineddepended strongly on the imaging conditions. Schuth and co-workers,43,44 used a two step approach to simulate thestructure of Yttria coated SBA-15 and MCM-41 materials.In the first step, a unit cell was generated from SiO2 and aweighted random placement of atoms was used to simulate adistribution of atoms inside the cell forming a continuous andsmooth transition from pore to wall. In the second step thestructure factors and the intensities of reflections were calcu-lated. They found a good comparison between the experimen-tal and simulated intensities of the powder diffraction pattern.Coasne and Pellenq45 studied the adsorption of argon in silicananopores of various shapes and sizes using gas chromatogra-phy with mass spectrometry (GC-MS). To model the structureof MCM-41 materials, they started with a crystoballite cubewith a cylindrical pore running through it. Kleestorfer and co-workers,46 modeled MCM-41 starting with a block of a-quartzand making a cylindrical hole inside it. They also found thatformation of interconnections between pores was energeticallyhighly unfavorable. They determined that the walls were non-crystalline and the pores were slightly hexagonal. Maddox andGubbins47 used a model that considered only oxygen atomsrandomly placed in a unit cell (with cylindrical annulus at thecenter and quarter pores at each corner of the lattice) to forman amorphous array. Bhatia and co-workers48 studied theMCM-41 by treating them as smooth cylindrical pores.In the present paper, we have developed various models

representing the structure of SBA-15 and MCM-41. H-ZSM-5unit cell was then introduced on the mesopore surface of thesematerials and the entire structure was optimized. The finalstructure was characterized using several techniques such assmall angle and wide angle X-ray scattering, Connolly surfacearea, accessible pore volume by nitrogen and argon adsorptionand methane adsorption isotherm at 303 K.

2. Simulation methods

2.1 Fabrication of SBA-15 structure

The method of Feutson and Higgins41 was modified to developthe SBA-15 model. The details have been provided in ourearlier manuscript.49–52 The key characteristics of the SBA-15model include:� Randomly placed spherical (or cylindrical) cavities present

in the walls of SBA-15. These cavities resemble the HR-TEMimages of SBA-15 reported by Liu et al.53 The majority of thesecavities were either interconnected or opening to the mainmesopore channel. The shape of these cavities does not remainperfectly spherical/cylindrical after optimization.� The triblock copolymer template was approximated as a

set of dummy carbon atoms randomly placed in the unit cellforming a rod/tube for the mesopores. No template was usedfor micropores.� Bulk heterogeneity was introduced by unbonding several

Si–O bonds (ca. 5%) of the atoms placed on a quartz latticeand replacing them with hydroxyls.

Fig. 1 The t-plot analysis of nitrogen adsorption isotherms of SBA-15coated with ZSM-5 and uncoated SBA-15.

3502 P h y s . C h e m . C h e m . P h y s . , 2 0 0 5 , 7 , 3 5 0 1 – 3 5 0 6 T h i s j o u r n a l i s & T h e O w n e r S o c i e t i e s 2 0 0 5

Publ

ishe

d on

18

Aug

ust 2

005.

Dow

nloa

ded

by U

nive

rsity

of

Nor

th C

arol

ina

at C

hape

l Hill

on

29/1

0/20

14 1

5:17

:34.

View Article Online

� Surface hydroxyl concentration of SBA-15 was adjusted toca. 3 OH nm‘2 (by hydroxylating Si or adding hydrogen to Oatoms on the surface of SBA-15) close to the experimentalvalues reported in the literature.54

� The structure was optimized and then equilibrated at 300K by NVT to obtain minimum energy configuration. Themmff94x forcefield55 was used, stepsize of 2 fs was chosenand the simulations were carried out for more than 100 ps. Thecavity shape in the final structure was no longer perfectlyspherical. The simulations and X-ray characterization wasperformed using MOE55 and Cerius256 packages.

We tried several forcefields but selected mmff94x because thesimulated low angle X-ray and wide angle X-ray diffraction(radial distribution function) of the simulated MCM-41 (andSBA-15) structures matched the experimental results up to 0.6nm as shown in Fig. 2. As the forcefield provided good matchof simulations with experimental data from WAXS for MCM-41 and SBA-15, it will was assumed that it will be applicable toSBA-15/ZSM-5 hybrid structure.

The commercial packages such as VASP, MOE, Cerius2come with basic molecular dynamics codes (written in FOR-TRAN, SVL or Cþþ) where forcefields can be changed easilywithout touching the main MD codes (neighbor list, verletalgorithm, etc). Irrespective of programming language thesecodes usually use the procedure of Allen and Tildesly (mole-cular simulation of liquids)57 to program the MD codes. Wehave not modified any of these codes or developed any newcomputational technique. The codes used in the present workwere supplied by MOE.55

The Cartesian/PDB or other forms of ZSM-5 structures arereadily available on several websites. In the present work, theywere obtained from Accelrys Inc.56 Before introducing theZSM-5 inside the SBA-15, the bulk 3-D structure of ZSM-5was characterized using simulated X-ray diffraction. The XRDpattern matched the experimental pattern reported in theliterature. ZSM-5 pore structure consists of interconnecting

micropore channels of two types: elliptical (5.1 � 5.6 A); andnear circular in cross-section (5.4 � 5.6 A). More details on thepore structure and atom ordering have been widely studied andthe reader is requested to read standard textbooks (e.g. Ruth-ven58) or use Internet search engine Google using ZSM-5 as akeyword.To introduce ZSM-5 in SBA-15, the following procedure

was followed:� The unit cell of the ZSM-5 (with terminal atoms ended by

H) was introduced near the surface of SBA-15. The 100 facewas parallel to the surface of the pore. We also tried a few otherorientations. However, the orientation does not change theproperties of the hybrid materials being studied. It has beenreported by experimental studies that ZSM-5 may crystallize atthe active sites present on the surface. Rather than computingindividual active sites and placing the ZSM-5, we have opti-mized the structure of H-ZSM-5 separately and allowed theZSM-5/SBA-15 structure to come to a lowest energy config-uration by molecular dynamics.� The entire structure was equilibrated for 100 ps or more

until the temperature remains constant (within 10 K) in NVEsimulations. During the simulations, the rebonding was carriedout to form a covalent bond between the SBA-15 surface andZSM-5 and if there are any excess hydrogens or hydroxylspresent on the surface, they were removed to satisfy thevalency.� The final structure was characterized using small angle as

well as wide angle X-ray scattering. The small angle X-rayscattering results match those of the original structure reportedby Newalkar et al.23 The wide angle X-ray scattering results areclose to the experimental WAXS results of hybrid structurereported by Mokaya and co-workers.59

� The final structure was used for adsorption of methane. Tothe present date, the only experimental data available formethane adsorption on SBA-15 is that of Newalkar et al.23

We have used all the experimental data points provided in theirmanuscript. The experimental data reported in their paper onlyspans up to ca. 200 kPa and does not cover the capillarycondensation region. It may be useful to use the experimentaldata of Seaton’s group to study the capillary condensationregion. However, the data is for MCM-41 and such a studyfocuses on the properties of condensed fluids in confinedmedia, opening up a debate in the area of reason for capillarycondensation, hysteresis and related thermodynamic/classicalarguments. We believe that such a study is beyond the scope ofthe present work. Several other reputed investigators includingSeaton,33 Schuth,43 Neimark,37 Gubbins,47 Do38 and Bhatia48

are working in this area and readers are requested to read theirwork.

3. Results

The visualization of a 3 � 3 � 1 structure of SBA-15 is shownin Fig. 3a. It represents the SBA-15 sample reported by New-alkar et al.23 They have reported the synthesis and character-ization of highly ordered SBA-15 with mesopore size of 7.3 nmhaving a narrow distribution (half peak width ca. 0.5–1 nm)and sharp peaks in the low angle X-ray diffraction region. Thecrystallite/grain size obtained from line broadening of the lowangle X-ray peaks is ca. 20–30 nm. The SBA-15 model devel-oped in the present work utilizes the periodic structure in 3-Dand simulated a single unit cell of SBA-15. Introducing the sizedistribution of mesopores would require simulation of severalhundred thousand atoms (a super-cell with a large number ofunit cells of different mesopore sizes to get good statisticalaverage). Such a study would need significant computationalresources which are not accessible at present.The unit cell parameters are 18.18 � 10.5 � 4 nm while the

diameter of the main mesopore channels is 7.3 nm. In order tounderstand the structure of SBA-15, a visualization of CMK-3

Fig. 2 (a) Comparison of simulated and experimental X-ray diffrac-tion pattern of structure MCM-41. (b) The radial distribution functionobtained using wide angle X-ray scattering results.50

P h y s . C h e m . C h e m . P h y s . , 2 0 0 5 , 7 , 3 5 0 1 – 3 5 0 6 3503T h i s j o u r n a l i s & T h e O w n e r S o c i e t i e s 2 0 0 5

Publ

ishe

d on

18

Aug

ust 2

005.

Dow

nloa

ded

by U

nive

rsity

of

Nor

th C

arol

ina

at C

hape

l Hill

on

29/1

0/20

14 1

5:17

:34.

View Article Online

structure developed in our earlier work52 is presented in Fig.3b. CMK-3 is mesoporous carbon and is considered to be anear negative replica of SBA-15. The equilibrated final struc-ture of a unit cell of MCM-41 and SBA-15 with zeolites ZSM-5in the mesopore channel is shown in Fig. 4a and 4b, respec-tively. In both structures we have presented results with 100orientation parallel to the surface. The MCM-41 model repre-sents a highly ordered structure of MCM-41 sample of Edleret al.39 The accessible micro- and mesopore surface of theZSM-5 and SBA-15 obtained using the Connolly procedure isshown in Fig. 5a and 5b, respectively. This is the first time thatthe Connolly procedure has been used to study the accessibilityof nitrogen molecule in the micro- and mesopores of SBA-15.The Connolly surface area of SBA-15 was found to be 780 m2

g�1 while that of ZSM-5 was 405 m2 g�1, close to the reportedvalues in the literature.23 The surface area of the compositesurface was found to be 710 m2 g�1 while the total pore volumewas found to be 0.85 cm2 g�1. As expected, the values are lowerthan the uncoated SBA-15.

The simulated X-ray diffraction patterns of the SBA-15structures used in Fig. 3a are shown in Fig. 5. The simulatedXRD patterns match well with the experimental XRD patternsreported in the literature.23 The comparison of experimentaland simulated XRD pattern of MCM-41 is shown in Fig. 2ausing the experimental data of White and co-workers. How-

ever, such a comparison is not shown in Fig. 6 for SBA-15because Newalkar et al.23 have not reported the XRD pattern.In order to understand the ZSM-5/SBA-15 hybrid structure,

the entire structure was filled with argon by placing Ar atomsrandomly and then equilibrating by NVT while freezing theatoms in the SBA-15/ZSM-5 structure. The snapshot of onlyAr atoms (SBA-15 and ZSM-5 are removed to avoid confu-sion) is shown in Fig. 7. A cavity related to the ZSM-5 on thesurface of SBA-15 can be seen in Fig. 7.The adsorption of methane at 303 K was carried out on

SBA-15. A snapshot at a pressure of 100 kPa is shown in Fig. 8and the corresponding simulated and experimental isotherm isshown in Fig. 9. All the experimental points reported byNewalkar et al.23 are shown in Fig. 9. The experimental datareported by Newalkar for SBA-15 does not cover capillarycondensation region. Unfortunately, that is the only dataavailable in the literature for SBA-15. It may be interestingto study the capillary condensation of methane in SBA-15,however such a study could open up a debate about capillarycondensation/hysteresis and the thermodynamic or molecularproperties of condensed fluids in confined media, which wouldbe a distraction from the main focus that is presenting the

Fig. 3 Visualization of SBA-1551and CMK-352 models studied in thepresent work.

Fig. 4 Snapshot of ZSM-5 encapsulated in MCM-41 and SBA-15.

Fig. 5 Connolly surface area of ZSM-5 unit cell and SBA-15.51

Fig. 6 Simulated X-ray diffraction pattern of SBA-15.51 The experi-mental data is not available for the material reported by Newalkaret al.23

Fig. 7 Snapshot of argon adsorption in SBA-15/ZSM-5 hybridstructure at 87 K.

3504 P h y s . C h e m . C h e m . P h y s . , 2 0 0 5 , 7 , 3 5 0 1 – 3 5 0 6 T h i s j o u r n a l i s & T h e O w n e r S o c i e t i e s 2 0 0 5

Publ

ishe

d on

18

Aug

ust 2

005.

Dow

nloa

ded

by U

nive

rsity

of

Nor

th C

arol

ina

at C

hape

l Hill

on

29/1

0/20

14 1

5:17

:34.

View Article Online

structure of hybrid materials. Such a comprehensive study onpure MCM-41 has been conducted by a leading researcherSeaton (methane adsorption),33,34 Neimark,37 Gubbins47 andDo38 (nitrogen and argon adsorption) recently for orderedporous materials and readers are requested to refer to theirwork. As expected, the amount of methane adsorbed in theSBA-15/ZSM-5 composite is lower than the pure SBA-15.Obviously, the main reason behind this is that the adsorptionamount is plotted per unit weight of the catalyst; we haveconfirmed this by estimating the number of methane moleculesadsorbed per hexagonal unit cell of the SBA-15/ZSM-5 hybridstructure.

4. Conclusions

This work describes the first study of hybrid SBA-15/ZSM-5materials using molecular simulations. Several model struc-tures possessing the properties (e.g. periodic arrangement ofmesopores, random arrangement of micropores, surface hy-droxyls and bulk deformations) of SBA-15 are developed tomatch the sample reported in the literature. The 100 face of H-ZSM-5 unit cell was then placed on the surface and the entirestructure equilibrated to obtain the final configuration. Thecoated and uncoated SBA-15 materials were then characterizedusing small angle, wide angle X-ray scattering, Connolly sur-face area and accessible pore volume for nitrogen and argon.The orientation of ZSM-5 on the surface has no effect on thearea, volume or adsorption capacity. The simulated adsorptionisotherm of methane on SBA-15 matches closely the experi-ments. The simulated adsorption of methane on the hybridstructure is lower than the uncoated sample. The coatedstructure has a lower total pore volume as well as Connollysurface area. It was found that the existing procedure of

coating SBA-15 by ZSM-5 reported by Do et al.1 should bemodified as it blocks all the micropores in the walls of the SBA-15 as well as ZSM-5 in the coated structure.

Acknowledgements

The author acknowledges Prof. Jennifer Wilcox, Prof. Yi HuMa, Prof. Pete Ludovice, Prof. Chris Jones, David Urban andAndrew Swann for useful discussions and help. The earlydevelopment of this work was funded by a grant from theUS DOE Office of Basic Energy Sciences through CatalysisScience contract number DE-FG02-03ER15459 (GT-UVAFocused Program in Catalysis by Immobilized Organometal-lics, Director and Principal Investigator (PI): Professor Chris-topher W. Jones and co-PI: Professor Peter J. Ludovice).

References

1 T.-O. Do, A. Nossov, M.-A. Springuel-Huet, C. Schneider, J. L.Bretherton, C. A. Fyfe and S. Kaliaguine, J. Am. Chem. Soc.,2004, 126, 14324.

2 J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T.Kresge, K. D. Schmitt, C. T-W. Chu, D. H. Olsen, E. W.Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker,J. Am. Chem. Soc., 1992, 114, 10835.

3 D. Y. Zhao, Q. S. Huo, J. L. Feng, B. F. Chmelka and G. D.Stucky, J. Am. Chem. Soc., 1998, 120, 6024.

4 M. Kruk, M. Jaroniec and A. Sayari, J. Phys. Chem. B, 1997, 101,583.

5 V. B. Fenelonov, A. Yu. Derevyankin, S. D. Kirik, L. A.Solovyov, A. N. Shmakov, J.-L. Bonardet, A. Gedeon and V.N. Rommanikov, Microporous Mesoporous Mater., 2001, 44, 33.

6 C. G. Sonwane, S. K. Bhatia and N. Calos, Ind. Eng. Chem. Res.,1998, 37, 2271.

7 C. G. Sonwane and S. K. Bhatia, Chem. Eng. Sci., 1998, 53, 3143.8 C. G. Sonwane and Q. Li, J. Phys. Chem. B, 2005, 109, 5691.9 C. G. Sonwane and S. K. Bhatia, J. Phys. Chem. B, 2000, 104,

9099.10 K. Miyazawa and S. Inagaki, Chem. Commun., 2000, 2121.11 M. Kruk, M. Jaroniec, T.-W. Kim and R. Ryoo, Chem. Mater.,

2003, 15, 2815.12 A. Galarneau, H. Cambon, F. D. Renzo and F. Fajula, Langmuir,

2001, 17, 8328.13 J. Liu, X. Zhang, Y. Han and F.-S. Xiao, Chem. Mater., 2002, 14,

2536.14 C. G. Goltner, B. Smarsly, B. Berton and M. Antonietti, Chem.

Mater., 2001, 13, 1617.15 Y. Ueno, A. Tate, O. Niwa, H.-S. Zhou, T. Yamada and I.

Honma, Chem. Commun., 2004, 6, 746.16 C. G. Sonwane and P. Ludovice, J. Mol. Catal. A: Chem., 2005,

238, 135.17 J.-S. Chang, J.-S. Hwang and S.-E. Park, Res. Chem. Int., 2003,

29, 921.18 L. Y. Shi, Y. M. Wang, A. Ji, L. Gao and Y. J. Wang, Mater.

Chem., 2005, 15, 1392.19 T. Yamada, H.-S. Zhou, H. Uchida, I. Honma and T. Katsube,

J. Phys. Chem. B, 2004, 108, 13341.20 Y. Xu, Q. Jiang, Y. Cao, Y. L. Wei, Z. Y. Yun, J. H. Xu, Y.

Wang, C. F. Zhou, L. Y. Shi and J. H. Zhu, Adv. Funct. Mater.,2004, 14, 1113.

21 M. J. Hudson, J. P. Knowles, P. J. F. Harris, D. B. Jackson, M. J.Chinn and J. L. Ward,Microporous Mesoporous Mater., 2004, 75,121.

22 M. Vallet-Regi, J. C. Doadrio, A. L. Doadrio, I. Izquierdo-Barbaand J. Perez-Pariente, Solid State Ionics, 2004, 172, 435.

23 B. L. Newalkar, N. V. Choudary, U. T. Turaga, R. P. Vijaya-lakshmi, P. Kumar, S. Komarneni and T. S. G. Bhat, Chem.Mater., 2003, 15, 1474.

24 A. Katiyar, L. Ji, P. Smirniotis and N. G. Pinto, J. Chromatogr.,A, 2005, 1069, 119.

25 H. Shiotsuka, T. Imamura, T. Nomoto and M. Ogawa, PCT Int.Appl., WO 2005016971, 2005.

26 M. L. Gray, Y. Soong, K. J. Champagne, H. W. Pennline, J.Baltrus, R. W. Stevens Jr, R. Khatri and S. S. C. Chuang, Int. J.Environ. Technol. Manage., 2004, 4, 82.

27 Y.-S. Ooi, R. Zakaria, A. R. Mohamed and S. Bhatia, EnergyFuels, 2005, in press.

28 Q. Lu, F. Gao, S. Komarneni and T. E. Mallouk, J. Am. Chem.Soc., 2004, 126, 8650.

Fig. 8 Snapshot of methane adsorption in the SBA-15/ZSM-5 hybridstructure.

Fig. 9 Methane adsorption isotherm on SBA-15 at 303 K.

P h y s . C h e m . C h e m . P h y s . , 2 0 0 5 , 7 , 3 5 0 1 – 3 5 0 6 3505T h i s j o u r n a l i s & T h e O w n e r S o c i e t i e s 2 0 0 5

Publ

ishe

d on

18

Aug

ust 2

005.

Dow

nloa

ded

by U

nive

rsity

of

Nor

th C

arol

ina

at C

hape

l Hill

on

29/1

0/20

14 1

5:17

:34.

View Article Online

29 S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T.Ohsuna and O. Terasaki, J. Am. Chem. Soc., 2000, 122, 10712.

30 V. Meynen, E. Beyers, P. Cool, E. F. Vansant, M. Mertens, H.Weyten, O. I. Lebedev and G. V. Tendeloo, Chem. Commun.,2004, 898.

31 T.-O. Do and S. Kaliaguine, Angew. Chem., 2002, 114, 1078.32 A. Sakthivel, S.-J. Huang, W.-H. Chen, W.-H. Chen, Z.-H. Lan,

K.-H. Chen, T.-W. Kim, R. Ryoo, A. S. T. Chiang and S.-B. Liu,Chem. Mater., 2004, 16, 3168.

33 Y. He and N. Seaton, Langmuir, 2003, 19, 10132.34 J.-H. Yun, T. Duren, F. J. Keil and N. A. Seaton, Langmuir, 2002,

18, 2693.35 B. Kuchta, P. Llewellyn, R. Denoyel and L. Firlej, Colloids Surf.,

A, 2004, 241, 137.36 D. Cao, Z. Shen, J. Chen and X. Zhang,Microporous Mesoporous

Mater., 2004, 67, 159.37 P. I. Ravikovitch, D. Wei, W. T. Chueh, G. L. Haller and A. V.

Neimark, J. Phys. Chem. B, 1997, 101, 3671.38 E. A. Ustinov and D. D. Do, J. Phys. Chem. B, 2005, 109, 1947.39 K. J. Edler, P. A. Raynolds, J. W. White and D. Cockson,

J. Chem. Soc., Faraday Trans., 1997, 93, 199.40 L. A. Solovyov, S. D. Kirik, A. N. Shmakov and V. N. Roman-

nikov, Microporous Mesoporous Mater., 2001, 44, 17.41 B. P. Feutson and J. B. Higgins, J. Phys. Chem., 1994, 16, 4459.42 C. A. Koh, R. E. Westacott, R. I. Nooney, V. Boissel, S. F. Tahir

and V. Tricarico, Mol. Phys., 2002, 100, 2087.43 S. Schacht, M. Janicke and F. Schuth, Microporous Mesoporous

Mater., 1998, 22, 485.

44 J. Sauer, F. Marlow and F. Schuth, Phys. Chem. Chem. Phys.,2001, 3, 5579.

45 B. Coasne and R. J.-M. Pellenq, J. Chem. Phys., 2004, 120, 2913.46 K. Kleestorfer, H. Vinek and A. Jentys, J. Mol. Catal. A: Chem.,

2001, 166, 53.47 M. W. Maddox and K. E. Gubbins, Langmuir, 1997, 13, 1737.48 S. K. Bhatia and D. Nicholson, Phys. Rev. Lett., 2003, 16105/

1-016105/4.49 C. G. Sonwane and P. J. Ludovice, J. Mol. Catal. A: Chem., 2005,

238, 135.50 C. G. Sonwane, C. W. Jones and P. J. Ludovice, J. Phys. Chem. B,

2005, submitted.51 C. G. Sonwane, J. M. Richardson, C. W. Jones and P. J.

Ludovice,MicroporousMesoporous Mater., 2005, to be submitted.52 C. G. Sonwane, J. Chromatogr., A, 2005, submitted.53 J. Liu, X. Zhang, Y. Han and F.-S. Xiao, Chem. Mater., 2002, 14,

2536.54 Ilja. G. Shenderovich, G. Buntkowsky, A. Schreiber, E. Gedat, S.

Sharif, J. Albrecht, N. S. Golubev, G. H. Findenegg and H.-H.Limbach, J. Phys. Chem. B, 2003, 107, 11924.

55 MOE, Molecular Operating Environment, Chemical ComputingGroup Inc., Release 2004.03.

56 Cerius2 Modeling Environment, Release 4.6, Accelrys Inc.57 M. P. Allen and D. J. Tildesly, Computer Simulation of Liquids,

Oxford University Press, Oxford, 1989.58 D. Ruthven, Principles of Adsorption and Adsorption Processes,

Wiley, New York, 1984.59 Z. Yang, Y. Xia and R. Mokaya, Adv. Mater., 2004, 16, 727.

3506 P h y s . C h e m . C h e m . P h y s . , 2 0 0 5 , 7 , 3 5 0 1 – 3 5 0 6 T h i s j o u r n a l i s & T h e O w n e r S o c i e t i e s 2 0 0 5

Publ

ishe

d on

18

Aug

ust 2

005.

Dow

nloa

ded

by U

nive

rsity

of

Nor

th C

arol

ina

at C

hape

l Hill

on

29/1

0/20

14 1

5:17

:34.

View Article Online