J O U R N A L O F C H E M I S T R Y Materials Communication Novel honeycomb structure: a microporous ZSM-5 and macroporous mullite composite Sridhar Komarneni,a Hiroaki Katsukib and Sachiko Furutab aMaterials Research Laboratory and Department of Agronomy, The Pennsylvania State University, University Park, PA 16802, USA. E-mail: komarneni@psu.edu bSaga Ceramics Research Laboratory, 3037-7, Arita-machi, Saga 844, Japan Received 22nd July 1998, Accepted 25th August 1998 We have developed a novel honeycomb composite struc- hydroxyls to reduce the deformation during final sintering at ture consisting of microporous ZSM-5 and macroporous 1650 °C.The calcined clay was ball-milled, dried and then mullite by in-situ crystallization of ZSM-5 utilizing glass thoroughly mixed with 10 wt % methyl cellulose binder and from a sintered kaolin honeycomb.This in-situ crystalliz- 25 wt% water before extrusion forming of a honeycomb of ation of ZSM-5 leads to better adhesion and mechanical 15×15×100 mm (cell size, 1.4×1.4 mm; wall thickness, strength for the zeolite film and results in a graded structure 510 mm). This extruded honeycomb was heated initially at with three layers consisting of strongly adhered ZSM-5 300 °C for 2 h to remove the binder and heated to 1650 °C at film at the surface, a composite ZSM-5 and mullite layer the rate of 2.2 °Cmin-1 followed by sintering at 1650 °C for below the pure ZSM-5 layer and porous mullite at the 2 h.The sintered body was determined to be composed of core. These novel composite structures are expected to 58 wt% mullite and 42 wt% silica glass.The silica glass in this have major applications in the areas of automotive sintered body was transformed to ZSM-5 zeolite in-situ and other catalysts, pervaporation membranes, cation by hydrothermal treatment at 190 °C for 14–28 days in exchange separations, etc. Teflon-lined hydrothermal vessels at autogenous pressure.The molar ratios of the starting chemicals for hydrothermal synthesis were as follows: SiO2 in honeycomb5NaOH5tetra- A novel composite honeycomb consisting of microporous propylammonium bromide (TPAB)5H2O=100512.8 (or ZSM-5 and macroporous mullite is developed with many 25.5)5552800. potential applications. The automotive industry utilizes cordi- First, a sintered honeycomb body of mullite and silica glass erite ceramic honeycomb structures in catalytic converters of was produced.By hydrothermally treating this honeycomb in gasoline-powered cars to reduce carbon monoxide, nitrous alkaline solutions, one can convert it into a porous mullite oxide and hydrocarbon emissions. The macroporous honeyhoneycomb, 10,11 by dissolving silica into the solution. By comb structures are also used in diesel-powered cars to trap treating this honeycomb with NaOH in the presence of TPAB and burn particulate carbon from the exhaust gases.In gasotemplate at 190 °C for two weeks, we converted the silica in line-powered cars a significant amount of the total emissions that a vehicle emits in a single trip are emitted in the first few minutes of operation1 because the operating temperature of the catalytic converter is below 300 °C at the very beginning of the trip.Below a 300 °C, the catalytic converter is ineVective in decomposing the various emissions while it has a maximum eYciency in the range 400–800 °C. A great deal of eVort at present is being devoted to reduce the emissions in the first few minutes by using electrically-heated catalysts.An alternative approach is to trap the hydrocarbon emissions until the catalytic converter reaches an operating temperature of 300 °C by using microporous adsorbents such as zeolites. Here we report the fabrication of a novel ZSM-5 (microporous)–mullite (macroporous) composite honeycomb structure which can be located at the entrance of the three-way catalyst and is potentially useful to trap the emissions until the catalytic converter reaches its operating temperature.There is also a great deal of interest in the preparation of composite materials containing continuous zeolite films for other applications such as catalysis, pervaporation, adsorption, cation exchange, etc..2–9 However, most of these studies led to limited success because of the problems of zeolite adhesion to the ceramic substrate.Here we overcome the adhesion problems by in-situ crystallization of ZSM-5 zeolite. Monolithic honeycomb was prepared from a commercially available New Zealand kaolin clay. The kaolin (halloysite) powder supplied by New Zealand Clay Company has the Fig. 1 Cross-section of honeycomb body showing (A) four layers of following chemical composition: SiO2, 50.07; Al2O3, 35.76; ZSM-5, ZSM-5+mullite, porous mullite and mullite+glass upon Fe2O3, 0.26; TiO2, 0.07; CaO, trace; MgO, 0.08; Na2O, 0.07; hydrothermal treatment with 12.8 M NaOH at 190 °C, 14 days and K2O, 0.01 and ignition loss, 13.79 wt%.This powder was first (B) three layers of ZSM-5, ZSM-5+mullite and porous mullite upon hydrothermal treatment with 25.5 M NaOH at 190 °C, 14 days.calcined at 500 °C for 3 h to remove adsorbed water and J. Mater. Chem., 1998, 8(11), 2327–2329 2327Fig. 2 Cross-section at higher magnification showing ZSM-5 layer, ZSM-5 plus mullite layer and porous mullite after hydrothermal treatment at 190 °C, 21 days. Fig. 5 Morphology of porous mullite after hydrothermal leaching of glass at 190 °C, 21 days.Table 1 The eVect of time and concentration of NaOH on the surface area of zeolite–mullite composites Hydrothermal conditionsa Time/days Amount of NaOH/mol Surface area/m2 g-1 7 25.5 43.7 14 25.5 76.2 21 25.5 92.2 7 12.8 60.9 14 12.8 78.3 21 12.8 82.7 Fig. 3 Powder X-ray diVraction pattern of ZSM-5 and porous mullite 28 12.8 110.8 composite prepared at 190 °C for 14 days.aHydrothermal conditions: 190 °C; autogeneous pressure and molar ratios, SiO2 in kaolin5NaOH5TPABr5H2O=1005(12.8, 25.5)5 552800. the honeycomb to ZSM-5 zeolite. Fig. 1A shows the initial conversion of the honeycomb to four layers from the surface to the core as follows: ZSM-5 on the surface, ZSM-5+mullite below the surface, porous mullite and mullite+glass at the phology of the porous mullite with an average pore size of about 0.57 mm.10 The results presented here clearly show that core.By continuing the treatment for three weeks, we completely converted all the glass to ZSM-5 zeolite with a sequence a novel microporous–macroporous composite was prepared with a very high surface area (Table 1). The adhesion and of three layers as follows: ZSM-5 layer on the surface, ZSM- 5+mullite below the surface and porous mullite at the core compressive strengths of a zeolite film with a thickness of 200 mm on the surface of the porous mullite were found to be (Fig. 1B). A cross-section of this novel composite clearly shows ZSM-5 on the surface followed by ZSM-5 + mullite very good and are in the ranges of 9–17MPa and 319–483 MPa, respectively.complex and porous mullite (Fig. 2). Powder X-ray diVraction patterns of the composite showed mullite and ZSM-5 crystal- We heated this porous mullite with a zeolite film of 200 mm at 900 °C for 60 h to determine its thermal stability and found line phases only (Fig. 3). Scanning electron micrographs of ZSM-5 from the surface show that a continuous layer of this it to be very stable with no cracks or pinholes.The surface areas of several samples heated at 900 °C were determined to phase had formed (Fig. 4). The size of the ZSM-5 crystals ranged from 20 to 60 mm. Fig. 5 shows the needle-like mor- be in the range of 80–100 m2 g-1. Thus we have fabricated a Fig. 4 Morphology of continuous zeolite film on the surface of the honeycomb at two diVerent magnifications.This film was prepared at 190 °C, 14 days in 12.8 M NaOH solution. 2328 J. Mater. Chem., 1998, 8(11), 2327–23292 J. G. Tsikoyiannis and W. O. Haag, Zeolites, 1992, 12, 126. novel microporous ZSM-5 and macroporous mullite composite 3 E. R. Geus, H. V. Bekkum, W. J. W. Bakker and J. A. Moulijn, with excellent mechanical properties and very high surface Microporous Mater., 1993, 1, 131.areas. This combination of mechanical properties, micro- and 4 M-D. Jia, K-V. Peinemann and R-D. Behling, J. Membr. Sci., macro-porosities with a high surface area has never been 1993, 82, 15. achieved before and these composites are expected to find 5 S. Yamazaki and K. Tsutsumi, Microporous Mater., 1995, 4, 205. 6 V. Valtchev, S. Mintova, B. Schoeman, L. 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Porous Mater., 1997, American Institute of Physics, College Park, MD, 1995, 3, 127. pp. 20–24. Communication 8/05724I J. Mater. Chem., 1998, 8(11), 2327–2329 2329