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[2] a) Y. Yang, Q. Pei, A. J. Heeger, J. Appl. Phys. 1996, 79, 934. b) J. Stampfl, S. Tasch, G. Leising, U. Schert, Synth. Met. 1995, 71, 2125. c) W-X. Jing, A. Kraft, S. C. Moratti, J. Gruner, F. Cacialli, P. J. Hamer, A. B. Holmes, R. H. Friend, Synth. Met. 1994, 67, 161. d) G. Grem, G. Leising, Synth. Met. 1993, 57, 4105. [3] a) E. Arias, T. Maillou, I. Moggio, D. Guillon, J. Le Moigne, B. Geffroy, Synth. Met. 2002, 127, 229. b) C. Schmitz, P. Posch, M. Thelakkat, H.-W. Schmidt, A. Montali, K. Feldman, P. Smith, C. Weder, Adv. Funct. Mater. 2001, 11, 41. c) N. G. Pschirer, T. Miteva, U. Evans, R. S. Roberts, A. R. Marshall, D. Neher, M. L. Myrick, U. H. F. Bunz, Chem. Mater. 2001, 13, 2691. d) X. Zhan, Y. Liu, G. Yu, X. Wu, D. Zhu, R. Sun, D. Wang, A. J. Epstein, J. Mater. Chem. 2001, 11, 1606. e) S. H. Lee, T. Nakamura, T. Tsutsui, Org. Lett. 2001, 3, 2005. f) A. Montali, P. Smith, C. Weder, Synth. Met. 1998, 97, 123. g) M. Hirohata, K. Tada, T. Kawai, M. Onoda, K. Yoshino, Synth. Met. 1997, 85, 1273. h) S. Tasch, E. J. W. List, C. Hochfilzer, G. Leising, P. Schlichting, U. Rohr, Y. Geerts, U. Scherf, K. Mullen, Phys. Rev. B. 1997, 56, 4479. i) S. A. Jeglinski, O. Amir, X. Wei, Z. V. Vardeny, J. Shinar, T. Cerkvenik, W. Chen, T. J. Barton, Appl. Phys. Lett. 1995, 67, 3960. j) K. Yoshino, K. Tada, M. Onoda, Jpn. J. Appl. Phys., Part 2 1994, 33, 1785. [4] P. M. Cotts, T. M. Swager, Q. Zhou, Macromolecules 1996, 29, 7323. [5] C. A. Breen, T. Deng, T. Breiner, E. L. Thomas, T. M. Swager, J. Am. Chem. Soc. 2003, 125, 9942. [6] Z. G. Zhu, T. M. Swager, Org. Lett. 2001, 3, 3471. [7] H. Mattoussi, H. Murata, C. D. Merritt, Y. Iizumi, J. Kido, Z. H. Kafafi, J. Appl. Phys. 1999, 86, 2642. [8] S. Coe, W.-K. Woo, M. Bawendi, V. Bulovic, Nature 2002, 420, 800. [9] V. Bulovic, V. B. Khalfin, G. Gu, P. E. Burrows, D. Z. Garbuzov, S. R. Forrest, Phys. Rev. B 1998, 58, 3730. [10] a) S. Tasch, G. Kranzelbinder, G. Leising, U. Scherf, Phys. Rev. B 1997, 55, 5097. b) M. Deussen, M. Scheidler, H. Bassler, Synth. Met. 1995, 73, 123.

Single Crystals of ZSM-5/Silicalite Composites**
By Manabu Miyamoto, Takashi Kamei, Norikazu Nishiyama,* Yasuyuki Egashira, and Korekazu Ueyama
The processes of the formation of dialkylbenzenes from monoalkylbenzene, such as disproportionation and alkylation, are among the most important in the chemical industry. These processes were carried out using solid acid catalysts in earlier times. The activity of these catalysts, such as silica±alumina, was low. Since the late 1960s, ZSM-5 catalysts have been extensively

±

[*] Dr. N. Nishiyama, M. Miyamoto, T. Kamei, Dr. Y. Egashira, Prof. K. Ueyama Division of Chemical Engineering Graduate School of Engineering Science Osaka University 1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan) E-mail: nisiyama@cheng.es.osaka-u.ac.jp [**] The authors thank M. Kawashima and the GHAS laboratory at Osaka University for the FE-SEM measurements. M. Miyamoto expresses his special thanks for the center of excellence (21COE) program Creation of Integrated EcoChemistry of Osaka University'.

studied because of their much higher selectivity for para-isomers, which are the most valuable compounds for commercial use. However, para-selectivity significantly decreases because of the acid sites on the external surface and the size of the pore openings. Hence, surface modification and pore size control have been proposed in order to enhance the selectivity.[1±9] On the other hand, zeolites have been studied for membrane separation techniques,[10±13] as well as for catalysis, for a long time. In the last decades, combined chemical reactors with zeolite membranes have been of great interest and a lot of applications have been reported.[14±21] Compared with conventional chemical reactors, membrane reactors have great advantages, such as higher selectivity and/or yield of products, simplification of processes, and inhibition of catalyst poisoning. However, the main issue of membrane reactors is the lower permeation rate than the reaction rate. Due to the low permeation flux, a significantly large membrane area and thin zeolite membrane are required. However, the synthesis of large zeolite membranes without any defects, like pinholes or cracks, and a method of controlling the membrane thickness have not yet been established. Recently, we have proposed a particle level membrane reactor. A catalyst particle has been coated with a permselective membrane.[22,23] The platinum-loaded TiO2 particles (particle size = 0.6 mm) coated with a silicalite-1 membrane showed high product selectivity in the hydrogenation of hex-1-ene (1-Hex) and 3,3-dimethylbut-1-ene (3,3-DMB) mixtures. The 1-Hex/3,3-DMB selectivity was 20 because of selective permeation of 1-Hex through the silicalite-1 membrane.[23] Silica± alumina catalyst particles (particle size = 1 mm) were coated with silicalite-1 membranes (silicalite/silica±alumina) and used for the disproportionation of toluene to produce xylene isomers. The silicalite-1 coatings on catalyst particles enhanced the para-selectivity[22] because of selective removal of p-xylene through the silicalite-1 membrane. Toluene conversion, however, significantly decreased from 1.5 to 0.08 % with the coating because the thickness of the silicalite-1 membrane was large (40 lm), which limited the diffusion of the products. In addition, the catalytic activity of silica±alumina was not very high. To solve these problems, in this study we have developed a novel composite catalyst consisting of a zeolite crystal with an inactive thin layer. A silicalite-1 layer was grown on protonexchanged ZSM-5 crystals (silicalite/H-ZSM-5). The conventional zeolite films on porous supports as well as on the particles[22,23] mentioned above have consisted of an oriented or randomly oriented polycrystalline material. Their film thickness is from several micrometers to several tens of micrometers. On the other hand, in this study a thin layer of zeolite is grown on a small crystal of zeolite, whose crystal size is a few micrometers. The framework structure of the thin layer is the same as that of the substrate. This novel composite is expected to have a very thin layer without a crystal boundary. Figure 1 shows field-enhanced scanning electron microscopy (FE-SEM) images of uncoated H-ZSM-5 and silicalite/ H-ZSM-5 after hydrothermal synthesis for 24 h. The uncoated

Adv. Mater. 2005, 17, 1985±1988

DOI: 10.1002/adma.200500522

 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

1985

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Figure 1. FE-SEM images of a) uncoated H-ZSM-5 and b) silicalite/ H-ZSM-5 after synthesis for 24 h. Figure 2. SEM image of silicalite/H-ZSM-5 composites.

H-ZSM-5 crystal was rounded in shape and the crystal size was about 3 lm. After 24 h, complete overgrowth by silicalite-1 had occurred, as shown by the changed morphology. 3 h, the silicalite-1 crystals grew along the ZSM-5 crystal surThere were no small particles on the surface. To confirm that faces perpendicular to the a and b axes and the crystal boundno dissolution of uncoated H-ZSM-5 crystals occurs under the ary finally disappeared. present synthetic conditions, H-ZSM-5 crystals were hydroOn the crystal surface of ZSM-5 perpendicular to the c axis, thermally treated with an alkaline precursor solution (a mixcrystal growth was slow in the early stage (0±3 h). However, ture of tetrapropylammonium hydroxide (TPAOH), EtOH, after 6 h, the silicalite-1 crystal had grown rapidly in the c and water) but without a silica source. The uncoated H-ZSMdirection. The crystal growth rate of silicalite-1 in the c direc5 crystals did not dissolve in the synthesis solution because no tion is much higher than that of ZSM-5. Seemingly, the silicavisual change was observed after the hydrothermal treatment. lite-1 crystal can grow rapidly on the ZSM-5 surface perpenThe size of the silicalite/H-ZSM-5 crystals was very similar to dicular to the c axis after the other two surfaces of the ZSM-5 that of the original H-ZSM-5 crystals. The silicalite/ H-ZSM-5 looks like single crystals. The present silicalite-1 layer is extremely thin (< 200 nm) in the a and b directions compared with other polycrystalline silicalite-1 membranes that have been reported and possesses no crystal boundary in the layer. Figure 2 shows an SEM image of the silicalite/ H-ZSM-5 composites with low magnification. The surface of the H-ZSM-5 crystals seems to be fully covered with silicalite layers. Silicalite-1 crystals also formed by themselves, though the number of the crystals was small. However, the formation of silicalite-1 crystals was inhibited using the precursor solutions with a low concentration of tetrapropylammonium (TPA) ions. ZSM-5 crystals were fixed on a Cu substrate and silicalite-1 layers were grown on the ZSM-5 crystals under hydrothermal conditions. The morphology of the crystals was then observed by FE-SEM measurements. This procedure was repeated every 1 h to study the formation mechanism of a silicalite-1 layer. Figure 3 shows FE-SEM images of an uncoated H-ZSM-5 crystal and silicalite-1/H-ZSM-5 composites. We observed the same crystal for each measurement. After 1 h of synthesis, small silicalite crystals of less than 100 nm in diameter were formed on the ZSM-5 surface. The formed silicalite-1 crystals are long in the direction of the c axis of ZSM-5. Generally, the growth rate of the silicalite-1 crystals is high in the direction of the c axis. Figure 3. FE-SEM images of an uncoated H-ZSM-5 crystal and silicalite/H-ZSM-5 The silicalite-1 crystals must have oriented in the same composites during the first 6 h. Two different starting crystals are observed and direction as the substrate ZSM-5 crystals. After 2 and shown in (a) and (b).

1986

 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Adv. Mater. 2005, 17, 1985±1988

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crystals are covered with silicalite-1 crystals. The proposed model for the formation of silicalite-1 layers on a ZSM-5 crystal is shown in Figure 4. The surfaces of a ZSM-5 crystal perpendicular to the a and c axes are covered with thin silicalite-1 layers of less than 200 nm thickness although the silicalite-1 layer is thick in the c direction after 6±24 h synthesis.

b

c

a

Silicalite-1 crystal

ZSM-5 crystal

Silicalite-1 crystals grow along the surface.

Silicalite-1

Figure 4. Graphical illustration of the proposed model for the formation of a silicalite-1 layer on a ZSM-5 crystal.

The alkylation of toluene with methanol was carried out at 673 K over the uncoated H-ZSM-5 and silicalite/H-ZSM-5 catalysts. The molar fraction of p-xylene in all the xylene isomers produced is defined as the para-selectivity. Table 1 lists the toluene conversion, the aromatic product distribution, and the fraction of xylene isomers after 60 min of reaction. The para-selectivity over the uncoated ZSM-5 catalysts was higher
Table 1. The results of the alkylation of toluene with methanol over silicalite/H-ZSM-5 and H-ZSM-5.
Parameter Reaction temperature [K] W/F [kg catalyst mol±1 h] [a] Conversion of toluene [%] Product composition [%] benzene p-xylene m-xylene o-xylene ethylbenzene p-ethyltoluene m-ethyltoluene trimethylbenzene Fraction of xylenes [%] p-xylene m-xylene o-xylene 98.9 0.7 0.4 63.1 25.2 11.7 23 53 24 0.2 34.8 0.3 0.3 0.1 0.7 0.0 0.8 0.4 24.5 9.8 4.6 0.1 0.4 0.2 2.7 Silicalite/H-ZSM-5 H-ZSM-5 673 0.06 37.2 673 0.06 42.7 Thermodynamic equilibrium

than that of the thermodynamic equilibrium value (23 %). The main product inside a pore of H-ZSM-5 under the present reaction conditions must be p-xylene, and the isomerization of p-xylene to the other xylene isomers might have occurred on the external surface of the H-ZSM-5 crystals. The para-selectivities over the uncoated and coated H-ZSM5 catalysts were 63.1 and 98.9 %, respectively. The para-selectivity was significantly increased by the silicalite-1 coating, although the conversion of toluene decreased from 42.7 to 37.2 %. In addition, isomerization of xylene on the external surface of catalysts was inhibited by the inactive silicalite-1 layer because the fraction of by-products with a large molecular size, such as m-ethyltoluene and trimethylbenzenes, was significantly decreased over the silicalite/H-ZSM-5 catalyst. The decrease in the toluene conversion was explained by the diffusion resistance of the products. By diffusing through the permselective silicalite-1 layer, the produced p-xylene was selectively removed from the other isomers inside the H-ZSM-5 catalyst. The silicalite-1 layer must be extremely thin compared with the conventional zeolite membranes because toluene conversion is still high under these reaction conditions even after coating. We suggest that the pores of silicalite-1 were not plugged by the coating. The pore channels of silicalite-1 must be coaxially connected to the pores of the ZSM-5. The silicalite-1 layer on the ZSM-5 crystal surface perpendicular to the c axis was thicker than the other surfaces. However, reactants and products can diffuse only in straight channels along the b direction and in zigzag channels along the a direction of the ZSM-5/silicalite-1 composites. Thus, the relatively thick silicalite-1 layer perpendicular to the c axis is not a diffusion barrier for reactants and products. Zeolite overgrowth has been reported, such as FAU on EMT zeolite[24] and MCM-41 on FAU zeolite.[25] On the other hand, in this study zeolite layers were grown on the zeolite with the same framework structure, resulting in high coverage of ZSM-5 crystals with silicalite layers and high para-selectivity. This excellent, high para-selectivity can be explained by the selective removal of p-xylene from the other xylene isomers in the H-ZSM-5 catalyst and inhibition of isomerization on the external surface of the catalysts by the silicalite-1 coating. In addition to the high para-selectivity, toluene conversion was still high even after coating because the silicalite-1 layers on the H-ZSM-5 crystals were very thin. The single crystal-like composite must be defect-free and have no crystal boundary to result in the excellent reaction results. The single crystals with thin layers on their external surface proposed in this study are expected to develop as new shape-selective catalysts.

Experimental
Silicalite/H-ZSM-5 was prepared as follow: H-ZSM-5 (Tosoh Corporation Co., Ltd., crystal size = approx. 3 lm, SiO2/Al2O3 = 216) was used as a catalyst. The starting sol for synthesis of a silicalite-1 thin layer consisted of fumed silica (Aerosil 200) as silica source, TPAOH as template and alkali source, ethanol, and deionized water. The H-ZSM-5 crystals were placed in the bottom of the mixture sol with a molar ratio of SiO2/TPAOH/ethanol/H2O = 25:3:100:1500. The crystal-

[a] W/F: (weight of catalysts)/(molar feed rate of toluene).

Adv. Mater. 2005, 17, 1985±1988

www.advmat.de

 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

1987

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lization was carried out at 453 K for 24 h by hydrothermal synthesis without agitation. The products were calcined in air at 773 K for 6 h with a heating rate of 1 K min±1. The products were characterized by X-ray diffraction (XRD) recorded on a Rigaku MiniFlex using Cu Ka radiation, by scanning electron microscopy (SEM) using a Hitachi S-2250 microscope, and by field-emission scanning electron microscopy (FE-SEM) using a Hitachi S-5000L microscope at an acceleration voltage of 21 kV. For the study of the crystal growth by FE-SEM observation, ZSM-5 crystals were fixed on a Cu substrate. The catalytic activity and selectivity of silicalite/H-ZSM-5 were investigated for alkylation of toluene. The alkylation of toluene with methanol was performed using a fixed bed reactor made of quartz glass (internal diameter 4 mm) with a continuous flow system under atmospheric pressure. Equimolar reactants of toluene and methanol were fed with argon carrier gas. The catalysts weight was 0.05 g and reaction temperature was 673 K. The space time, W/F, which is the weight of the catalyst divided by the feed rate of toluene, was varied by changing the argon gas feed rate. Products were directly introduced into a Shimadzu GC-14B gas chromatograph equipped with a flame ionization detector. Received: March 14, 2005 Final version: May 21, 2005
[1] N. Y. Chen, W. W. Keading, F. G. Dwyer, J. Am. Chem. Soc. 1997, 101, 6783. [2] W. W. Kaeding, C. Chu, L. B. Young, B. Weinstein, S. A. Butter, J. Catal. 1981, 67, 159. [3] M. Niwa, M. Kato, T. Hattori, Y. Murakami, J. Phys. Chem. 1986, 90, 6233. [4] H. Vinek, J. A. Lercher, J. Mol. Catal. 1991, 64, 23. [5] T. Hibino, M. Niwa, Y. Murakami, J. Catal. 1991, 128, 551. [6] J.-H. Kim, A. Ishida, M. Okajima, M. Niwa, J. Catal. 1996, 161, 387. [7] Y.-G. Li, W.-H. Xie, S. Yong, Appl. Catal. A. 1997, 150, 231. [8] A. B. Halgeri, J. Das, Catal. Today 2002, 73, 65. [9] S. Zheng, H. R. Heydenrych, H. P. R?ger, A. Jentys, J. A. Lercher, Top. Catal. 2003, 22, 101. [10] H. Sakai, T. Tomita, T. Takahashi, Sep. Purif. Technol. 2001, 25, 297. [11] M. E. Davis, Science 2003, 300, 438. [12] Z. 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 2003, 300, 456. [13] W. Yuan, Y. S. Lin, W. Yang, J. Am. Chem. Soc. 2004, 126, 4776. [14] N. van de Puil, E. J. Creyghton, E. C. Rodenburg, T. S. Sie, H. van Bekkum, J. C. Jansen, J. Chem. Soc., Faraday Trans. 1996, 92, 4609. [15] J. M. van de Graaf, M. Zwiep, F. Kapteijn, J. A. Moulijn, Chem. Eng. Sci. 1999, 54, 1441. [16] J. M. van de Graaf, M. Zwiep, F. Kapteijn, J. A. Moulijn, Appl. Catal. A: Gen. 1999, 178, 225. [17] D. Casanave, P. Ciavarella, K. Fiaty, J. A. Dalmon, Chem. Eng. Sci. 1999, 54, 2807. [18] K. Tanaka, R. Yoshikawa, C. Ying, H. Kita, K. Okamoto, Catal. Today 2001, 67, 121. [19] Y. Hasegawa, K. Kusakabe, S. Morooka, J. Membr. Sci. 2001, 190, 1. [20] T. Masuda, T. Asanuma, M. Shouji, S. R. Mukai, M. Kawase, K. Hashimoto, Chem. Eng. Sci. 2003, 58, 649. [21] B.-H. Jeong, K. Sotowa, K. Kusakabe, J. Membr. Sci. 2003, 224, 151. [22] N. Nishiyama, M. Miyamoto, Y. Egashira, K. Ueyama, Chem. Commun. 2001, 1746. [23] N. Nishiyama, K. Ichioka, D.-H. Park, Y. Egashira, K. Ueyama, L. Gora, W. Zhu, F. Kapteijn, J. A. Moulijn, Ind. Eng. Chem. Res. 2004, 43, 1211. [24] A. L. Yonkeu, V. Buschmann, G. Miehe, H. Fuess, A. M. Goosses, J. A. Martens, Cryst. Eng. 2001, 4, 253. [25] K. R. Kloetstra, H. W. Zandbergen, J. C. Jansen, H. van Bekkum, Micropor. Mesopor. Mater. 1996, 6, 287.

Tetrathiafulvalene [FeIII(C2O4)Cl2]: An Organic±Inorganic Hybrid Exhibiting Canted Antiferromagnetism**
By Bin Zhang,* Zheming Wang, Hideki Fujiwara, Hayao Kobayashi,* Mohamedally Kurmoo, Katsuya Inoue, Takehiko Mori, Song Gao, Yan Zhang, and Daoben Zhu*
Over the past twenty years, the field of molecular materials has been confronted with a wide range of interesting compounds, based either on purely organic or inorganic molecules or on organic±inorganic hybrids, exhibiting diverse electrical, magnetic, and optical properties.[1] While several electrical and magnetic ground states have been established and very well documented in the literature, the possibility of introducing novel properties with organic±inorganic hybrids remains a big challenge to date. In addition to organic superconductivity in a magnetically dense compound,[2] and inorganic ferromagnetism in the presence of high organic conductivity,[3] several p±d interactions have been established.[4±6] The latter is exemplified by the observation of field-induced superconductivity,[4,5] a metamagnetism-driven superconductor±metal transition,[6] and, most recently, ferrimagnetism involving both organic donors and inorganic spins.[7] The key feature of these hybrids is the interaction through space or through weak supramolecular contacts. While this can be quite strong between nearest neighbors having strong p±p overlap, especially those containing chalcogenides, the interactions between p

±

±

[*] Prof. B. Zhang, Prof. D. Zhu Organic Solid Laboratory, CMS Institute of Chemistry, The Chinese Academy of Science Beijing 100080 (P.R. China) E-mail: zhangbin@iccas.ac.cn; zhudb@iccas.ac.cn Prof. B. Zhang, Prof. H. Kobayashi, Prof. Z. Wang, Dr. H. Fujiwara, Prof. K. Inoue Institute for Molecular Science and CREST Japan Science and Technology Corporation Okazaki 444-8585 (Japan) E-mail: hayao@ims.ac.jp Prof. M. Kurmoo Laboratoire de Chimie de Coordination Organique, CNRS-UMR7140 Universit? Louis Pasteur 4 rue Blaise Pascal, F-67000 Strasbourg Cedex 1 (France) Prof. T. Mori Department of Organic and Polymeric Materials Graduate School of Science and Engineering Tokyo Institute of Technology O-Okayama, Tokyo 152-8552 (Japan) Prof. Z. Wang, Prof. S. Gao The College of Chemical and Molecular Engineering Peking University Beijing 100871 (P.R. China) Y. Zhang Department of Physics, Peking University Beijing 100871 (P.R. China) [**] This research was supported by NSFC Nos. 20343001, 20473095, CMS-CX2003, SRF for ROCS, SEM, China and the CNRS, France.

1988

 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI: 10.1002/adma.200500766

Adv. Mater. 2005, 17, 1988±1991


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