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Microporous and Mesoporous Materials 97 (2006) 27–33

Polycrystalline films of epitaxial MFI overgrowths

Zheng Wang a, Qinghua Li a, Jonas Hedlund a,*, Anton-Jan Bons b

a Division of Chemical Technology, Lulea University of Technology, SE-97187 Lulea, Swedenb ExxonMobil Chemical Europe Inc., European Technology Center, Hermeslaan 2, B-1831 Machelen, Belgium

Received 6 October 2005; received in revised form 20 June 2006; accepted 21 June 2006Available online 12 September 2006

Abstract

Films of epitaxial MFI overgrowths, i.e. ZSM-5 films covered with silicalite-1, with crystals extending from the substrate to the topsurface, were synthesized using a seeding method with acid leaching between the synthesis of the MFI layers. The films were character-ized by SEM, TEM, XRD and XPS. When acid leaching was omitted, secondary nucleation of silicalite-1 on the ZSM-5 film resulted in asandwich film with discontinuous crystals. When the precursor ZSM-5 film was acid leached and the surface Si/Al ratio increased from23 to 47, the crystals in the precursor film grew epitaxially upon treatment in a silicalite-1 synthesis mixture. It was thus revealed thatreduction of the aluminum content at the external surface of ZSM-5 may be important for the successful synthesis of epitaxial MFI over-growths. Alternatively, acid leaching may provide a cleaner surface, and facilitate epitaxial growth.� 2006 Elsevier Inc. All rights reserved.

Keywords: Epitaxial MFI overgrowth; Film; Seeding method; Acid leaching; Zeolite

1. Introduction

MFI-type zeolite includes the synthetic species silicalite-1 and ZSM-5. Silicalite-1 is a pure silica analogue of ZSM-5, whereas ZSM-5 has a Si/Al ratio of 10 and upward toany finite number [1]. Framework aluminum atoms resultin acidity. Silicalite-1 is thus not an acid catalyst but aneffective adsorbent for organic molecules, whereas ZSM-5has considerably higher acidity and catalytic activity. TheMFI structure has a channel system consisting of straightcircular channels (5.4 A · 5.6 A) interconnecting withsinusoidal and elliptical channels (5.1 A · 5.4 A). Thewell-defined and narrow pores of ZSM-5 result in a uniqueshape selectivity in reactions such as toluene alkylation,alkyl-benzene disproportionation, dialkyl-benzene isomeri-zation and Fries rearrangement of aryl esters [2–8].

It is well-known that the acid sites located in the channelsystem (internal surface) of ZSM-5 play a major role in

1387-1811/$ - see front matter � 2006 Elsevier Inc. All rights reserved.

doi:10.1016/j.micromeso.2006.06.030

* Corresponding author. Tel.: +46 920 492105; fax: +46 920 491199.E-mail addresses: johe@ltu.se, Jonas.Hedlund@ltu.se (J. Hedlund).

shape selectivity. However, the acid sites on the externalsurface reduce the shape selectivity. The possibility to pas-sivate or remove aluminum from the external surface hasbecome a topic of increasing interest for enhancing theshape selectivity of ZSM-5 and other zeolites.

To enhance the shape selectivity of ZSM-5, various dea-lumination schemes have been applied. The most com-monly used method is hydrothermal dealumination, inwhich the zeolite is heated to high temperatures in a flowof steam. Unfortunately, hydrothermal treatment ofZSM-5 at severe conditions produces extra-framework alu-minum species by removal of aluminum atoms from theZSM-5 lattice. This aluminum forms larger agglomeratesin channels or on the surface [9,10]. A reduction of frame-work aluminum can reduce the total catalytic activity.Another scheme for dealumination of Al-rich zeolites isleaching with a mineral acid [11–13]. It has been shownthat only a limited extent of the external acid sites couldbe removed without significantly changing the catalyst interms of total acidity by acid leaching. Acid leaching istherefore usually combined with hydrothermal dealumina-tion to remove the extra-framework aluminum species

28 Z. Wang et al. / Microporous and Mesoporous Materials 97 (2006) 27–33

occluded in the pores of dealuminated zeolites, therebyreducing diffusion resistance during catalytic reaction.Chemical vapour deposition (CVD) or chemical liquiddeposition (CLD) of silicon alkoxides, such as tetraethox-ysilane (TEOS) and tetramethoxysilane (TMOS), is aneffective method for passivation of the external surface[14–19]. Silylation occurs preferably on the external surfaceand passivates the non-shape selective acid sites. However,an inert silica layer is deposited on the surface of the zeo-lites and the pore opening may therefore be narrowed oreven blocked, which will increase the diffusion resistanceand thus decrease the catalyst activity.

In summary, these methods aim at removing or blockingthe active acid sites on the external surface to improve theshape selectivity of ZSM-5 zeolites. These measures mayincrease the catalytic selectivity, but may also decreasethe activity.

A reduction of the active sites at the external surface canalso be achieved by epitaxial overgrowth of aluminum-freesilicalite-1 on the precursor ZSM-5 crystals. Such materialscould result in higher selectivity without narrowing thepore opening or affecting internal pore structure and acid-ity of the precursor ZSM-5 crystals. Zeolite overgrowthsopen possibilities for development of materials with opti-mized adsorption, diffusion and reactivity [20]. Epitaxyinvolves the oriented overgrowth of one crystalline solidupon another crystalline solid with different structure orcomposition [21]. Overgrowth zeolites with different struc-tures have been reported in literature, such as epitaxialovergrowth of FAU type zeolite on EMT crystals [21], zeo-lite b on SSZ-31 nano-fibers [22] and overgrowth of milli-meter-sized sodalite with cancrinite crystals [23]. Millerreported compositional overgrowth of ZSM-5 and silicla-ite-1 using a two-step procedure [24]. Adsorption studiesand catalytic testing of materials that are claimed to beZSM-5 crystals with a silicalite-1 coating have beenreported previously [25,26,15,27,28]. It was shown thatthe selectivity could be enhanced with only a slightly loweractivity. However, no additional characterization resultswere provided to show whether the resulting materials werepure epitaxial MFI overgrowths, i.e. with a continuouslypropagating channel system or just a physical mixture ofZSM-5 crystals and silicalite-1 crystals.

A seeding method invented by our laboratory has beensuccessfully used for the synthesis of thin zeolite filmsand membranes [29–36]. Zeolite films can potentially beexplored as structured adsorbents, structured catalysts,novel sensors, reactive or uncreative membranes [33,37–39]. Films of epitaxial overgrowths can undoubtedly alsobe applied in these novel applications and the propertiesof the film may be tailored by overgrowth. Recently, prep-arations of films of epitaxial MFI overgrowths were alsoreported by our group [40,41]. Films are well-suited for anumber of characterization tools, which together with thepossible new applications for films, explain the choice offilms rather than discrete crystals for the studies. In thesestudies [40,41], films could be grown epitaxially without a

discontinuity at the ZSM-5/silicalite-1 interface only whenthe precursor ZSM-5 film had a very low aluminumcontent (Si/Al = 90, purified bulk crystals, according toICP-AES) [40]. If a ZSM-5 film with very high aluminumcontent was used (Si/Al = 10, according to EDS), thegrowth was not epitaxial and a discontinuity occurred [41].

In the present work, the possibility to prepare films ofepitaxial MFI overgrowths with higher aluminum concen-tration in the precursor ZSM-5 film, by applying acidleaching, is described and the films are characterized bySEM, TEM, XPS and XRD.

2. Experimental

2.1. Seed adsorption

A silicalite-1 seed sol with an average crystal size of60 nm was prepared from a synthesis solution by two weeksof hydrothermal treatment at 60 �C. The synthesis solutionwas prepared by shaking tetrapropylammonium hydroxide(TPAOH, 2.0 M solution, Aldrich), tetraethyl orthosilicate(TEOS 98%, Aldrich) and distilled water for 24 h at roomtemperature. The molar composition of the synthesismixture was 9TPAOH:25SiO2:360H2O:100EtOH. Polishedquartz (0001) substrates were rinsed in acetone underultrasound treatment and with distilled water. The sub-strates were then treated in a solution of 0.4 wt% cationicpolymer (Redifloc 4150, Eka Chemicals AB, Sweden) indistilled water at pH = 8.0. The substrates were thenimmersed in a purified seed sol to adsorb silicalite-1 seeds.Details regarding seeding have been reported earlier [42].

2.2. Preparation of films of epitaxial MFI overgrowths

A two-step crystallization procedure including acidleaching between the synthesis steps was used for prepara-tion of epitaxial MFI overgrowths. The same chemicals asused for seed preparation were also used for film growth. Inthe first step, a precursor ZSM-5 film was grown at 100 �Cby treatment of the seeded supports in a clear synthesismixture with the molar composition 3TPAOH:0.25Al2O3:25SiO2:1600H2O:100EtOH:1.0Na2O. After 2 days ofcrystallization, the samples were rinsed with a 0.1 Mammonia solution and distilled water. The rinsed ZSM-5films were treated in an HCl solution (pH = 1) at 85 �Cfor 48 h, i.e. similar to the process used by Li et al. [43].Acid leached ZSM-5 films were subsequently immersed ina TPA–silicalite-1 synthesis solution with the molar com-position 3TPAOH:25SiO2:1600H2O:100EtOH. After 72 hof crystallization at 100 �C, the samples were finally rinsedwith a 0.1 M ammonia solution to remove sediments andsynthesis mixture from the film surface. Some samples werealso prepared by a similar two-step crystallization proce-dure but the acid treatment was omitted. For comparison,silicalite-1 films were also grown directly on quartz wafers.ZSM-5 films were also grown according to Li et al. [41]using a synthesis mixture with a molar composition of

Z. Wang et al. / Microporous and Mesoporous Materials 97 (2006) 27–33 29

3TPAOH:0.25Al2O3:25SiO2:1600H2O:100EtOH:0.1Na2Oand the synthesis was carried out at 100 �C for 72 h in thiscase. Please note that the sodium content was 10 timeslower in this case, which results in low concentration ofaluminum in the film.

2.3. Characterization

The seed size was measured with a Brookhaven Instru-ment BI200SM Dynamic light scattering system (DLS).A Philips XL 30 scanning electron microscope (SEM)equipped with a LaB6 emission source was used to studythe morphology and cross-sections of MFI films by mount-ing samples on stubs and covering them with a thin goldlayer prior to analysis. Microstructural analysis was carriedout by transmission electron microscopy (TEM), using aPhilips CM12T operated at 120 kV. Ultra-thin (<100 nm)cross-sections for TEM were prepared by focused ion beam(FIB) sectioning. Before FIB sectioning, the films werecoated with Pt for protection against the ion beam. TheFIB cross-sections were placed on holey carbon supportfilms for TEM observation. A Siemens D5000 X-ray dif-fractometer (XRD) using Cu Ka radiation was used todetermine the crystalline phase and preferred orientation.X-ray photoelectron spectroscopy (XPS) was used to ana-lyze the Si/Al ratio at the surface of the films. The XPS sig-nal emanates from the surface to a depth of 5–6 nm. XPSmeasurements were carried out before and after acid leach-ing on the ZSM-5 films prepared in the present work andfor comparison, also on ZSM-5 films prepared accordingto Li et al. [41].

3. Results and discussion

Fig. 1a and b shows SEM images of a silicalite-1 filmafter 72 h of hydrothermal synthesis. The film is smoothwith a constant thickness of about 500 nm. Some of thecrystals extend from the support to the film top surface.Fig. 1c and d shows a ZSM-5 film grown by 48 h hydro-thermal treatment at 100 �C. It should be noted that nofurther growth occurs after 48 h. The film is continuouswith a constant thickness of about 350 nm. Some of thecrystals seem to extend throughout the entire film, similarto the silicalite-1 case. By comparing the insets of Fig. 1aand c, it is clear that the surface of the ZSM-5 crystals ismore granular. Similar observations have been reportedearlier [44]. Furthermore, large embedded crystals (markedby an arrow) are present in the ZSM-5 film, but not in thesilicalite-1 film. The Si/Al ratio of the ZSM-5 film surfacemeasured by XPS was 23, i.e. the aluminum content onthe surface is quite high.

Fig. 1e shows a top-view image of a silicalite-1 filmgrown on a ZSM-5 film without acid leaching. The surfaceof the crystals is smooth, indicating that the top film con-sists of silicalite-1. Many embedded large crystals are visi-ble. The film is smoother between these large crystals andthe crystal size in these regions is similar to corresponding

regions in the sample consisting of a 500 nm silicalite-1 filmonly. This indicates that the crystals in the first film havenot grown epitaxially, because the crystals at the surfacewould be larger in that case. The side-view image of thesample, shown in Fig. 1f, supports this hypothesis. A dis-continuity is visible at the interface of the two layers. Thefilm thickness is about 900 nm, close to the sum of thethickness of the two individual ZSM-5 and silicalite-1 films.It seems that new silicalite-1 crystals nucleated on top ofthe ZSM-5 film, the latter only acting as a substrate, notas a seed layer. This may be the case if the nucleation rateis larger than the growth rate in the early stages of silicalite-1 growth or if there is an induction period for growth,allowing nucleation to occur. The latter suggestion seemsmore likely, since the nucleation rate is low in thesesystems. The columnar structure of the films shown inFig. 1b and d indicates a low nucleation rate comparedto the film growth rate. These observations agree with whatwe have reported earlier [45]. Li et al. [41] concluded thatepitaxial growth occurs when the compositional differencebetween the layers is relatively small, and the synthesis con-ditions are similar or when the first layer is silicalite-1. Ifthe first layer is ZSM-5 and the synthesis conditions and/or the composition vary too much, a discontinuity occursat the interface between the layers, and sandwiched filmresults, where nucleation of the second layer is initiatedby secondary nucleation or by applying seeds. Li et al.[41] reported epitaxial growth when the surface of the pre-cursor ZSM-5 film has a Si/Al ratio of 120 (measured byXPS in the present work). The synthesis mixture used forfilm growth in the present work contains 10 times moresodium than the synthesis mixture used by Li et al., whichfacilitates the incorporation of aluminum in the film. In thepresent work, a ZSM-5 film with quite high aluminum con-tent on the surface (Si/Al = 23) was used. It thus seems thatthe compositional difference between silicalite-1 and ZSM-5 in the present work is too large for epitaxial growth. Thismay lead to an induction time for continued film growth,allowing nucleation to occur. Alternatively, the surface ofthe ZSM-5 film is not clean enough, which may reducethe growth rate and allow nucleation to dominate. In thesample shown in Fig. 1e and f, it is unlikely that precursorfilm grew epitaxially and that the channel systems of theZSM-5 and silicalite-1 parts are connected.

Fig. 2a shows a bright-field (BF) TEM image of a layerof silicalite-1 grown directly on ZSM-5 without acid leach-ing. The contrast within the zeolite films is due to electrondiffraction; several crystals show dark contrast becausethey are in a strongly diffracting orientation. The interfacebetween the films is marked by a zone of nano-voids, 5–10 nm in size. Several crystals clearly nucleate at the inter-face, consistent with the SEM observations describedabove. Other precursor crystals appear to have grown epi-taxially; homogeneous contrast indicates that the crystalorientation is continuous across the interface. A high reso-lution lattice fringe image of one of those crystals clearlyshows that the lattice fringes are continuous across the

Fig. 1. SEM micrographs of the films. Top- and side-view images of a silicalite-1 film (a) and (b), a ZSM-5 film (c) and (d), a silicalite-1 film grown directlyon a ZSM-5 film without acid leaching (e) and (f), and a silicalite-1 film grown on an acid-treated ZSM-5 film (g) and (h). The magnification in the insets isfour times larger than indicated by the scale marker bar. Arrows indicate large embedded crystals.

30 Z. Wang et al. / Microporous and Mesoporous Materials 97 (2006) 27–33

interface (Fig. 2b) giving direct evidence for epitaxialgrowth and that the crystal structure, and hence the chan-nel system, is continuous.

Acid leaching of the precursor film was carried out inorder to study the effect on the growth. The Si/Al ratioon the surface increased to 47 after acid leaching, i.e. about

half of the aluminum was removed according to XPS. Sincethe acid leaching was carried out on a sample containingtemplate molecules, the crystals should not be affected bythe leaching process, as indicated by TEM [43].

Fig. 1g shows a top-view image of a silicalite-1 filmgrown on an acid leached ZSM-5 film. As before, the

Fig. 2. TEM micrographs of a silicalite-1 film grown directly on a ZSM-5 film without acid leaching. The bright-field image (a) shows the columnarcrystals in the films by diffraction contrast. The black layer on top is the protective Pt coating used during FIB sectioning, the background structure withrounded holes is the carbon support film used for TEM. The interface between ZSM-5 and silicalite-1 is marked by a series of nano-voids. The whitearrows indicate columnar crystals that have nucleated at the interface. Based on the diffraction contrast, some crystals appear to be continuous across theinterface (black arrows), which is confirmed by the lattice fringe image (b).

Z. Wang et al. / Microporous and Mesoporous Materials 97 (2006) 27–33 31

silicalite-1 crystals are smooth. Between the large embed-ded crystals, the film is built by crystals that are larger thanin corresponding regions in the sample consisting of a sili-calite-1 film only, see corresponding inset images. This indi-cates that the ZSM-5 crystals have grown epitaxially whentreated in the silicalite-1 synthesis mixture, resulting in anepitaxial MFI overgrowth with crystals extending fromthe substrate to the top surface. No discontinuity isobserved at the ZSM-5/silicalite-1 interface, see Fig. 1h.This result may be explained by the fact that there is noappreciable induction time for growth when the acid lea-ched ZSM-5 film is treated in the silicalite-1 synthesis mix-ture. This film is also slightly thicker (about 1 lm) than thesample prepared by omitting the acid leaching (about0.9 lm). Since the thickness exceeds the sum of the twoindividual films, this observation is somewhat surprising.Our experience is that the film growth rate is constant inthese systems [45]. A thicker film may also indicate thatthe induction time is null or short. However, the observeddifference in thickness is small and is not an evidence forepitaxial growth.

Fig. 3 shows bright-field TEM micrographs of a silica-lite-1 layer grown on acid leached ZSM-5. In this case itis clear that most of the crystals are continuous acrossthe interface. Although it was not possible to obtain latticefringe images of this sample, it is most likely that the crys-

tals grew epitaxially and that the channel system is contin-uous across the ZSM-5/silicalite-1 interface also in thiscase. Again, nano-voids are visible at the interface. Sincethe nano-voids are present in both leached and nonleachedfilms, the voids are probably related to the regrowth, andnot to the acid leaching step.

Fig. 4 shows XRD data of the precursor ZSM-5 film,and films prepared with or without acid leaching. As hasbeen reported earlier [31,42], that MFI films in this thick-ness range, prepared with this method, have a preferredorientation with a large fraction of the crystals orientedwith the a-axis perpendicular to the substrate surface.The XRD data for the samples in the present work alsosuggests this. For instance, the (50 1) reflection is verymuch stronger than the (051) reflection. In a randomly ori-ented sample, the intensity of the (051) reflection should beabout 80% of the (501) reflection. Except for variations intotal intensity (depending on the total film thickness) thedata is very similar for all samples, which shows that thepreferred orientation of the crystals does not change appre-ciably from sample to sample. This is expected for epitaxialovergrowths. In that case, the preferred orientation of thecrystals in the precursor film should transfer to the secondfilm. If the sample is not an epitaxial MFI overgrowth, butjust two separate MFI films, the preferred orientationshould also be unaffected. As was shown in previous work

Fig. 3. Bright-field TEM micrographs of a silicalite-1 film grown on an acid-treated ZSM-5 film, (a) overview and (b) detail. The majority of the crystalsare continuous across the interface. The interface is marked by nano-voids. Black arrows indicate crystals that are continuous across the interface.

Fig. 4. XRD patterns of the precursor ZSM-5 film (a), of the ZSM-5/silicalite-1 composite prepared by omitting the acid leaching (b) andthe ZSM-5/silicalite-1 composite prepared by employing acid leaching (c).The reflection labelled with * emanates from the aluminum holder and thebackground at 2h > 24.1� is due to the quartz substrate.

32 Z. Wang et al. / Microporous and Mesoporous Materials 97 (2006) 27–33

[42], the preferred orientation develops towards one withthe a-axis perpendicular to the substrate surface due tocompetitive growth during hydrothermal treatment. Evenif the new silicalite-1 nuclei that form on the non-acidleached precursor ZSM-5 film are randomly oriented, ana-oriented film may develop due to competitive growth.However, the nuclei may also have some preferred orienta-tion, but that is not reflected by the XRD data from theserelatively thick films since the orientation is developed dur-ing growth.

4. Conclusions

This work has shown that epitaxial growth does notoccur when a precursor ZSM-5 film with a surface Si/Alof 23 is treated in a silicalite-1 synthesis mixture. Instead,a sandwich film, in which the silicalite-1 part mostly growsfrom new nuclei at the precursor ZSM-5 surface, isobtained. When the precursor ZSM-5 film is acid leachedso that the surface Si/Al is 47, the crystals in the precursorfilm grows epitaxially in the silicalite-1 synthesis mixture.The aluminum content on the surface of the precursorZSM-5 film may play a crucial role for epitaxial growth.These films can potentially be used in a number of applica-tions such as structured adsorbents, structured catalysts,

Z. Wang et al. / Microporous and Mesoporous Materials 97 (2006) 27–33 33

sensors, reactive or uncreative membranes, etc., and theproperties of the film may be tailored by applying over-growth in addition to standard modification techniquessuch as control of film thickness, ion-exchange, adjustmentof Si/Al ratio, etc.

Acknowledgments

Financial support from the Swedish Research Council(VR) is gratefully acknowledged. We thank Dr. ChenggeJiao of the FIB Laboratory of FEI UK Ltd. in Bristol,UK, for the FIB sectioning of the TEM samples.

References

[1] R. Szostak, Handbook of Molecular Sieves, Van Nostrand Reinhold,New York, 1992.

[2] T. Yashima, Y. Sakaguchi, S. Namba, Stud. Surf. Sci. 7 (1981) 739.[3] A. Vogt, H.W. Kouwenhoven, R. Prins, Appl. Catal. A 123 (1995) 37.[4] G. Eder-Mirth, H.D. Wanzenbock, J.A. Lercher, in: H.K. Beyer,

H.G. Karge, I. Kiricsi, J.B. Nagy (Eds.), Catalysis by MicroporousMaterials, Studies in Surface Science and Catalysis, vol. 94, Elsevier,Amsterdam, 1995, p. 449.

[5] Y.S. Bhat, J. Das, A.B. Halgeri, Appl. Catal. A 122 (1995) 161.[6] L.Y. Fang, S.B. Liu, I. Wang, J. Catal. 185 (1999) 33.[7] N. Arsenova, H. Bludau, R. Schumacher, W.O. Haag, H.G. Karge,

E. Brunner, U. Wild, J. Catal. 191 (2000) 326.[8] W.H. Chen, T.C. Tsai, S.J. Jong, Q. Zhao, C.T. Tsai, I. Wang, H.K.

Lee, S.B. Liu, J. Mol. Catal. A: Chem. 181 (2002) 41.[9] J. Datka, S. Marschmeyer, T. Neubauer, J. Meusinger, H. Papp,

F.-W. Schutze, I. Szpyt, J. Phys. Chem. 100 (1996) 14451.[10] E. Brunner, H. Ernst, D. Freude, T. Frohlich, M. Hunger, H. Pfeifer,

J. Catal. 127 (1991) 34.[11] P.J. Kooyman, P. van der Waal, H. van Bekkum, Zeolites 18 (1997)

50.[12] T. Sano, Y. Uno, Z.B. Wang, C.-H. Ahn, K. Soga, Micropor.

Mesopor. Mater. 31 (1999) 89.[13] A. Omegna, M. Haouas, A. Kogelbauer, R. Prins, Micropor.

Mesopor. Mater. 46 (2001) 177.[14] M. Niwa, N. Katada, T. Murakami, J. Phys. Chem. 94 (1990) 6441.[15] R.W. Weber, J.C.Q. Fletcher, K.P. Moller, C.T. O’Connor, Micro-

por. Mater. 7 (1996) 15.[16] H.P. Poger, M. Kramer, K.P. Moller, C.T. O’Connor, Micropor.

Mesopor. Mater. 21 (1998) 607.[17] A.B. Halgeri, J. Das, Catal. Today 73 (2002) 65.[18] C. Grundling, G. Eder-Mirth, J.A. Lercher, J. Catal. 160 (1996) 299.[19] S. Zheng, H.R. Heydenrych, A. Jentys, J.A. Lercher, J. Phys. Chem.

B 106 (2002) 9552.[20] J.A. Martens, P.A. Jacobs, Adv. Funct. Mater. 11 (2001) 337.

[21] A.M. Goossens, B.H. Wouters, V. Buschmann, J.A. Martens, Adv.Mater. 11 (1999) 561.

[22] S. Nair, L.A. Villaescusa, M.A. Camblor, M. Tsapatsis, Chem.Commun. (1999) 921.

[23] T. Okubo, T. Wakihara, J. Plevert, S. Nair, M. Tsapatsis, Y. Ogawa,H. Komiyama, M.E. Davis, Angew. Chem. Int. Ed. 40 (2001)1069.

[24] S.J. Miller, US Patent 4,394,251, 1983.[25] C.S. Lee, T.J. Park, W.Y. Lee, Appl. Catal. A 96 (1993) 151.[26] L.D. Rollmann, US Patent 4088605, 1976.[27] H.P. Roger, K.P. Moller, C.T. O’Connor, Micropor. Mater. 8 (1997)

151.[28] H.P. Roger, K.P. Moller, C.T. O’Connor, in: A. Corma, F.V. Melo,

S. Mendioroz, J.L.G. Fierro (Eds.), 12th International Congress onCatalysis, Studies in Surface Science and Catalysis, vol. 130, Elsevier,Amsterdam, 2000, p. 2909.

[29] J. Hedlund, B. Schoeman, J. Sterte, Int. Pat. Appl. WO 97/33684,1997.

[30] J. Hedlund, B. Schoeman, J. Sterte, Micropor. Mesopor. Mater. 38(2000) 25.

[31] Z. Wang, J. Hedlund, J. Sterte, Micropor. Mesopor. Mater. 52 (2002)191.

[32] Z. Wang, M. Grahn, M.L. Larsson, A. Holmgren, J. Hedlund, Chem.Commun. 24 (2004) 2888.

[33] M. Grahn, Z. Wang, M.L. Larsson, A. Holmgren, J. Hedlund, J.Sterte, Micropor. Mesopor. Mater. 81 (2005) 357.

[34] M. Lassinantti, F. Jareman, J. Hedlund, D. Greaser, J. Sterte, Catal.Today 67 (2001) 109.

[35] J. Sterte, J. Hedlund, D. Creaser, O. Ohrman, Z. Wang, M.Lassinantti, Q. Li, F. Jareman, Catal. Today 69 (2001) 323.

[36] J. Hedlund, F. Jareman, A.J. Bons, M. Anthonis, J. Membr. Sci. 222(2003) 163.

[37] E.E. McLeary, J.C. Jansen, F. Kapteijn, Micropor. Mesopor. Mater.90 (2006) 198.

[38] Z.P. Lai, G. Bonilla, I. Diaz, J.G. Nery, K. Sujaoti, M.A. Amat, E.Kokkoli, O. Terasaki, R.W. Thompson, M. Tsapatsis, D.G. Vlachos,Science 300 (2003) 456.

[39] P. Ciavarella, D. Casanave, H. Moueddeb, S. Miachon, K. Fiaty, J.A.Dalmon, Catal. Today 67 (2001) 177.

[40] Q. Li, J. Hedlund, D. Creaser, J. Sterte, Chem. Commun. 6 (2001)527.

[41] Q. Li, J. Hedlund, J. Sterte, D. Creaser, A.J. Bons, Micropor.Mesopor. Mater. 56 (2002) 291.

[42] J. Hedlund, S. Mintova, J. Sterte, Micropor. Mesopor. Mater. 28(1999) 185.

[43] Q. Li, Z. Wang, D. Creaser, H. Zhang, X.D. Zou, J. Hedlund,Micropor. Mesopor. Mater. 78 (2005) 1.

[44] A.E. Persson, B.J. Schoeman, J. Sterte, J.-E-. Otterstedt, Zeolites 15(1995) 611.

[45] Q. Li, D. Creaser, J. Sterte, Mciropor. Mesopor. Mater. 31 (1999)141.