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initial reaction, by coke and aromatic precursors that are not formed on HZSM-5.
Frillette, V. J.; b a g , W. 0.; Lago, R. M. J . Cafal. 1981, 6 7 , 218-222. Good, 0 . M.; Voge, H. H.; Greensfelder, E. S. Ind. Eng. Chem. 1949, 39, 1032- 1036. Greensfelder, B. S.; Voge, H. H. Ind. Eng. Chem. 1945, 37, 514-520. Haag, W. 0.; Lago, R. M.; Weisz, P. E. Faraday Discuss. Chem. SOC.1981, 72, 317-330. Jacobs, P. A,; Martens, J. A,; Weltkamp, J.; Beyer, H. K. Faraday Discuss. Chem. SOC.1981, 72, 353-369. Janardhan. P. B.: Raieswari. S. Ind. €no. Chem. Prod. Res. D e v . 1977. 76. 52-58. KO,A. N.; Wojciechowski, B. W. Prog. React. Kinet. 1983, 12(4), 201-262. Kobolakis, I.; Wojciechowski, B. W. Can. J . Chem. Eng. 1985, 6 3 , 269. Nace, D. M. Ind. Eng. Chem. Prod. Res. D e v . 1969, 8 , 24-31. Pansing, W. F. J . fhys. Chem. 1965, 69, 392-396. Poutsm, M. L. "ZeoliteChemistry and Catalysis", Rabo, J. A,, Ed.; American Chemlcal Society: Washington, DC, 1976 ACS Monograph Ser. No. 171, pp 437-528. Sherzer, J.; Rltter, R. E. Ind. Eng. Chem. Prod. Res. Dev. 1978, 77, 219-223.
Acknowledgment
This work was supported by the Natural Science and Engineering Council of Canada.
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L i t e r a t u r e Cited Abbot, J.; Wojciechowski, B. W. Can. J . Chem. Eng. 1985, in press. Best, D.; Wojciechowski, B. W. J . Cafal. 1977, 4 7 , 11-27. Best, D. A.: Patchovsky, R.; Wojciechowski, B. W. Can. J . Chem. Eng. 1971, 49, 809-812. Corma, A.; Planelles, J. H.; Sanches-Mariu, J.; Thomas, F. J . Cafal. 1985, 9 2 , 284. Corm, A.; Mouton, J. E.; Orchili&, A. V. Ind. Eng. Chem. Prod. Res. Dev. 1984a, 23, 404. Corma, A.; Juan, J.; Martos, J.; Molina, J. Proc. Inf. Congr. Cafal., 8th 1984b. 293. Chen, N. Y.; Garwood, W. E. J . Catal. 1978, 52, 453-458. Chen, N. Y.: Lucki, S. J.; Mower, E. B. J . Catal. 1989, 73, 328-332. Derouane, E. G. Sfud. Surf. Scl. Catal. 1980, 5 , 5-18.
Received for reuiew December 18, 1984 Revised manuscript received April 16, 1985 Accepted May 18, 1985
Synthesis and Crystal Growth of Zeolite ZSM-5 from Sodium Aluminosilicate Systems Free of Organic Templates Eiichl Narlta' Department of Liberal Arts and Engineering Sciences, Hachlnohe Natlonal College of Technology, Tamonokl, Hachlnohe, Aomori 03 1, JaDan
Keiichi Sato, Noboru Yatabe, and Taljiro Okabe Department of Applied Chemistry, Faculty of Englneerlng, Tohoku Universlty, Aramaki, Sendai 980, Japan
When the reaction mixture of (a = 0.10-0.25)Na20-(b = 0.002-0.05)A1203-Si02-46H,0 is heated at 190 O C for 24 h, hydrous sillcon(1V) oxide, aquartz, zeolie ZSM-5, and mordenite were formed as a single crystalline phase or as a binary mixture of these four compounds, depending on the a and b values. The addition of small amounts of seed crystals (ZSM-5, silicalie, aquartz) and acetone in the reaction mixture resulted in the formation of ZSMd which had a high degree of crystallization and a narrow crystal size distribution in the (0.10-0.25)Na20-(0.0050.02)Ai2O3-Si0,-46H,0-(O.7- 1.3)acetone system at short synthesis times. Acetone, added in the reaction mixture, inhibited the spontaneous formation of ZSM-5 nuclei and accelerated the crystallization of ZSM-5 on the seed crystals. The apparent activation energy for crystal growth was determined to be 76 kJ mol-' at a = 0.15. The effects of various factors influencing the crystal growth of ZSMd were also investigated, and a new synthesis method of ZSM-5 using no organic templates was proposed on the basis of the results.
Introduction
A highly siliceous zeolite, ZSM-5, developed by Mobil Oil Corp., shows outstanding properties as a shape-selective catalyst for a number of industrially important processes because of its unique channel structure (Butter et al., 1975; Chang et al., 1975; Meisel et al., 1976). In addition, the intrinsic hydrophobic surface of ZSM-5 enables it to be used as a new type of adsorbent for organic compounds in water (Chen and Miale, 1982; Takahashi and Nakamoto, 1982; Milestone and Bibby; 1983). This ZSM-5 is conventionally synthesized by heating a reactive aluminosilicate gel containing the sodium-tetrapropylammonium (Na-TPA) cation as a template under hydrothermal conditions (Chang et al., 1975). Since the patent on ZSM-5 was issued from Mobil Oil Corp., a number of studies have actively been carried out for the synthesis of ZSM-5, and 0196-4321/85/ 1224-0507$01.50/0
most of these studies are concerned with searching for new organic templates available for the crystallization of ZSM-5. Thus, many alternate methods, characterized by the use of various organic templates in place of organic ammonium ions, are presently known (Weisz, 1980; Koizumi and Ueda, 1983; Rollman, 1984). These organic bases, however, are poisonous and industrially expensive. Therefore, in order to extend the potential usefulness of ZSM-5 into many fields, the developement of additional advantageous methods, both technical and economical, is indispensable. We have previously shown that ZSM-5, having a high degree of crystallization and a narrow crystal size distribution, can be obtained from an aluminosilicate system containing a small amount of acetone by using ZSM-5 seed crystals as crystallization nuclei at short synthesis times 0 1985 American Chemical Society
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281'. CuKo
Figure I. X-ray diffraction pattern of the ZSM-5 seed crystals.
Table I. Products Obtained in the aNa,O-bAI,O,-Si0,-46H,O System at 190 O C for 24 h b(SiO,/Al,O,) a 0.002 (500) 0 . ~ (zoo) 5 0.01 (IOO) 0.02 (50) 0.06 (20) 0.10 amoP amor amor amor amor 0.15 SiOZb amor ZSM-5 amor amor 0.20 SiOz SiOp ZSM-5 amor amor ("-quartz)' 0.25 SiO, amor ZSM-5 mordenite amor (n-quartz) (SiO,) 'Amorphous substance. 'Hydrous silieon(1V) oxide (ASTM card 31-1233). 'Minority.
U
'w Figure 2. Scanning electron miemgraph of the ZSMd seed m)stals.
(Narita et el., 1984). However, studies of the various faetonr influencing the crystal growth of ZSM-5 were still insufficient. The reason for and the mechanism of the acceleration of ZSM-5 crystallization by adding acetone in this system were also still unclear. In this study, we first investigated the crystallization behavior of ZSM-5 and other crystalline phases from the unseeded system. The effect of the addition of seed crystals and acetone on the crystal growth of ZSM-5 under various hydrothermal conditions was then investigated in order to develop the new synthesis method of ZSM-5 using no organic templates. Experimental Section Reaction Materials. The reaction materials used for the synthesis were colloidal silica (Snowtex-30 from Nissen Chemical Ind., Ltd., 3(t31% SiO,), aluminum sulfate (AI,(SO,),.14-18H,O), sodium hydroxide, and acetone (all Wako Pure Chemical Ind., Ltd., guaranteed reagents). ZSM-5 seed Crystals. ZSM-5 seed crystals used in this study were synthesized according to the patent of Mobil Oil Corp. (Chang et al., 1975), except the amount of water in the reaction mixture was decreased to obtain smallersized crystals of ZSM-B; i.e., the precursor was first crystallized from a reaction mixture composed of 0.06(TPA),011.13Na20-0.01Al~03-Si02-13H,0 a t 170 OC for 3 days and then calcined a t 600 "C for 1 h to remove the obstructing organic compounds from its channel. An X-ray diffraction pattern of ZSM-5 seed crystals is shown in Figure 1. The diffraction pattern revealed that the seed crystals were ZSM-5. The scanning electron micrograph of ZSM-5 seed crystals is shown in Figure 2. The mean particle size was 0.19 Fm, and the surface area, as measured by using the single point BET method, was 441 m2 g-I. The Si02/A1203ratio was 77. Silicalite (the aluminum-free analogue of ZSM-5) seed crystals were synthesized by the same method previously described. The product may contain a very small amount of aluminum as an impurity. Crystallization Procedure. First, 10 g of sodium aluminosilicate gel having definite composition was prepared by using the reaction materials in a polypropylene beaker. The mixture was then put in a stainless-steel
autoclave (20 mL) and maintained a t 150-230 "C under autogenwus pressure without agitation for crystallization. When the crystallization syntheses were carried out in the seeded system containing acetone, the seed crystals and acetone were mixed homogeneously with the reaction mixture before the mixture was charged in the autoclave. A 10% NaOH solution was used at the hydrothermal condition to clean the autoclave before every run to dissolve possible product from previous runs. After crystallization, solid products were separated from the suspension by centrifugation, washed repeatedly with distilled water, and then dried over P20&a t room temperature under reduced pressure. Analysis. The products were identified by X-ray diffraction by using a Rigaku Denki Geigerflex 2013 with Ni-filtered Cu K a radiation a t 30 kV and 10 mA. The observation of the products was performed by using a Hitachi-Akashi scanning electron microscope MSM 4C102. The percent of crystallization of ZSM-5 and a-quartz was estimated by using X-ray diffraction as previously reported (Narita et al., 1984). The SiO, content in the product was determined by the gravimetric method. Atomic absorption spectroscopy was used for the determination of the aluminum content. The Si0,/A1203ratio was calculated from the resulting data. Results a n d Discussion Crystallization of ZSM-5 from Unseeded System. The kind of products obtained in the reaction mixtures of aNa20-bAI2O3-SiO2-46H2O a t 190 OC for 24 h are summarized in Table I. In the region of b = 0.01,ZSM-5 was crystallized under the conditions of a = 0.15-0.25, although the products were 2&30% crystallized. In the region of b > 0.02, no ZSM-5 was found; however, increasing the synthesis time to 48 h also provided the formation of ZSM-5 in the region of b = 0.02. This result agreed with that reported by the earlier workers (Grose and Flanigen, 1981; Dai et al., 1983). No 7SM-5 was found in the region of b < 0.005, and the crystallization of hydrous silicon(1V) oxide instead of ZSM-5 occurred. The hydrous silicon(1V) oxide detected here is a special type formed only under hydrothermal conditions. Along with an increase in the a value, Le., in alkalinity, the resulting hydrous silicon(1V) oxide was gradually transformed into a-quartz. In the region of poor aluminum content, silica was found to crystallize as follows: amorphous SiO, hydrous silicon(1V) oxide a-quartz. It was concluded that 7SM-5 was formed even in the reaction mixtures that were free of organic template by selecting appropriate Na20/Si02 and Si02/A120, ratios. Figure 3 shows the X-ray diffraction patterns of the typical products given in Table I. Sample A (hydrous silicon(1V) oxide) and sample B (ZSM-5) have low diffraction peaks, while sample C (mordenite) has considerably high diffraction peaks. No crystalline products other than these three were found in this study.
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m Mordenile
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I
I
201'. CuKm
281.. CUKQ
Figure 3. X-raydiffraction patterns of the typical products obtained in the nNa,O-bAI2O3SiO246H2Osystem at 190 "C far 24 h A. (I = 0.15. b = 0.002:B. (I = 0.20, b = 0.01: C, o = 0.25. b = 0.02.
3 $1'
Figure 6. X-raydiffraction patterns of the typical produds (A> k , and k,, was found to occur over the range of experimental conditions studied. The implications of such a network in kinetic parameter evaluation are discussed. Optimized kinetic parameters, which permit prediction of reaction rate given the bulk gas composition and temperature, were derived from the experimental kinetic data for each of these reactions by using a model that accounts for pore-diffusion as well as external transport limitations. The rather unique nature of the reaction network warranted the use of such a model, which was later justified by the results.
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Introduction
The CO-NO-02-H20 reaction system includes two of the major reactions (viz. CO-02 and CO-NO) associated with catalytic cleanup of automotive exhaust gas. Intrinsic
* To whom correspondence shouid be addressed. 'Present address: Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, KS 66045. 0 196-432 1/85/1224-05 12$0 1.50/0
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kinetic parameters are reported here for this reaction system on a commercial three-way catalyst (TWC). The kinetic data for this purpose were obtained by using a fixed-bed with external recycle reactor. Intrinsic kinetic expressions are necessary for the rational design of catalytic converters. Kinetic parameters have been reported for oxidation of CO and C3H, in the presence of NO and H 2 0 on a Pt/r-A120, catalyst (Voltz 0 1985 American Chemical
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