J. MATER. CHEM., 1994, 4( 5), 735-739 New Route for Dispersion of Inorganic Salts onto the Channel Surfaces of Microporous Crystals: High Dispersion of CuCI, in Zeolites using a Microwave Technique Feng-Shou Xiao, Wenguo Xu, Shilun Qiu and Ruren Xu* Key Laboratory of Inorganic Hydrothermal Synthesis and Department of Chemistry, Jilin University, Changchun 730023, People's Republic of China A series of CuCI,-zeolites with a weight ratio of CuCI,.2H,O:zeolites of 0.1 0-0.80 have been prepared. After the reaction of CuCI,.2H20 with zeolite in a microwave oven for 10-20 min at ambient temperature, the CuCI,-zeolites (CuCI,.2H20 :NaZSM-5 =0.10-0.50; CuCI,.2H,O :NaY =0.1-0.60) showed only those X-ray peaks assigned to zeolites, the characteristic peaks of the CuCI,.2H20 having disappeared completely, which suggests that the CuCI, is highly dispersed in the channels of NaZSM-5 and NaY zeolites.Similar phenomena were observed for the samples of CuCI,-silicalite-I, AuCI,-Nay, AuCI,-NaZSM-5, NiCI,-NaZSM-5, RuCI,-Nay, Li2S04-AIP04-1 1. The n-hexane isotherms of CuC12-NaZSM-5 treated in a microwave oven exhibited a higher adsorption pressure to reach saturated adsorption of n-hexane, compared with those of NaZSM-5 and a mechanical mixture of NaZSM-5 and CuCI,.2H20 without treatment in a microwave oven. IR spectra of CO adsorbed on CuCI,-NaZSM-5 treated in a microwave oven showed much stronger adsorption bands than those of CuZSM-5 ion-exchanged by CuCI, solution, which indicates that the concen- tration of Cu2+ (CO) and Cuf (CO) on the CuCI,-NaZSM-5 is larger than those on the CuZSM-5.Furthermore, CuC12.2H20-NaZSM-5 (weight ratio 0-0.50) exhibited no peak at the melting point of CuCI, in DTA curves, because the CuCI, was highly dispersed in the channels of NaZSM-5. However, increasing the CuCl2.2H,O loading in NaZSM-5 up to 0.60, beyond the high-dispersion capacity, the DTA curve exhibited peaks at 770 K assigned to the melting point of CuCI, due to residual crystalline CuCI,. The forms of the active components present in heterogeneous In the present paper, we try to develop a new route for the catalysts are of importance to catalysis. A supported catalyst dispersion of some inorganic salts onto channel surfaces of usually consists of active components dispersed on a support microporous crystals.As an example, we study the dispersion with a highly specific surface. The degree of dispersion of the of CuCl, in NaZSM-5 and NaY zeolites using the microwave active component on the support is of economic consequence method, and it is found that the CuC1, highly disperses in the and influences the activity and selectivity of the catalysts.'-5 pores of NaZSM-5 and NaY zeolites. One method for obtaining high dispersity of the active compo- nent onto the support is the so-called 'monolayer disper- sion',&-'' which is thermodynamically stable. Recently, Iwamoto et ~l."-'~ reported that copper ion- Experimental exchanged zeolites, in particular copper ion-exchanged Preparation of SamplesNaZSM-5 zeolites, are very active for catalytic decomposition of nitrogen monoxide (NO).This and the stoichiometry of CuCl2-NaZSM-5 and CuC1,-NaY were prepared from the reaction were further confirmed by the other research- CuC1,.2H20 (purity >99.99%) with NaZSM-5 (Si :A1 =40, ers,'+-'' and increasing interest in this field has been fuelled surface area 500 m2 g-') and NaY (Si:Al=2.75, surface area by various environmental concerns.18-20 The activity and 750 m2 g-I), respectively. The NaZSM-5 (Nay) powder selectivity in catalytic decomposition of NO are strongly (2.00 g) was mixed mechanically with CuC1,.2H20 crystals influenced by the copper loading in zeolites and the properties (0-1.60 g), and the sample was placed in the microwave oven of zeolite^.'^^'^^'^ The preparation of Cu-zeolites is usually (Microwave Products, Shunde, China; model, E-100EA; fre- performed by the ion-exchange method.Owing to the limi- quency, 2450 MHz; power, 800 W). After reaction for tation of the ion-exchanged amount in zeolites,2'*22 it is 10-60 min, the sample was characterized by X-ray diffraction difficult to prepare Cu-zeolites with a high Cu content (e.g. (D/max-IIIA, Rigaku). The CuZSM-5 sample (Cu :Al =0.40)samples with Cu: Al> 1.0).Additionally, it is well known that was prepared from Cu2+-exchange in 0.1 mol 1-' CuC1,zeolites containing various cations exhibit high catalytic aqueous solution with NaZSM-5 at room temperature for activity and selectivity in many catalytic reaction^:^-^^ and several hours. the preparation of zeolites exchanged by cations with higher content such as ReY (Re =rare-earth cation) and NH4ZSM-5 is not simple.Generally, these samples were prepared by repeated cycles of cation-exchange of zeolites, drying and Hexane Isotherm Measurements calcination.26 In this decade commercially available microwave ovens The hexane isotherms on various samples were carried out have been used in many laboratory including with a Cahn-2000 electron recording balance, equipped with the preparation of short-lived radio- temperature control and weight monitor units, connected to organic synthe~is,~~,~' pharmaceutical^,^' the dissolution of geological samples in a vacuum system consisting of an oil diffusion pump backed mineral acid,33 the reaction of solids in the synthesis of up by a mechanical pump.The sample was first placed into inorganic and the crystallization of NaA zeo- a sample cell, and evacuated at 473 K for 3 h. After the sample lite.35 More recently, we have successfully used the microwave had been cooled to room temperature, it was exposed to technique to synthesize some molecular ~ieves~~?~~ hexane and its weight change was recorded. The sensitivity ofat ambient temperature with short reaction time (5-30 min). the electron recording balance was 0.1 pg. 736 Infrared Spectroscopy The sample was pressed into a self-supporting disc (10 mm diameter, 5-5.5 mgcm-, mass) and placed in an infrared quartz cell with CaF, windows. After evacuation from room temperature to 573 K for 5 h and at 573 K for 2 h to remove adsorbed water and other impurities, the sample disc was cooled to room temperature.Then CO 100Torr was intro- duced into the cell, and infrared spectra were measured using a Fourier transform spectrometer (Nicolet 5DX) with a reso- lution of 2 cm-' in the region 4000-1200 cm-'. Thermal Analysis Differential thermal analysis (DTA) was recorded in a flow of pure nitrogen on a PE-1700 by programmed heating at 10 K min-'. Results and Discussion X-Ray Diffraction Fig. 1 shows the XRD patterns of NaZSM-5 zeolite with CuC12.2H20 under microwave conditions. As observed in Fig. l(u) and l(b), the two XRD patterns give the same peaks at 7.9", 8.9" and 23.1", characteristic of NaZSM-5, which indicates that the framework structures of NaZSM-5 are stable under microwave conditions.The mechanical mixture u.-v)c u .-c J. MATER. CHEM., 1994, VOL. 4 of CuC12.2H,0 and NaZSM-5 (CuC12.2H,0 : NaZSM-5 = 0.10; Cu: Al= 1.5) shows peaks at 16.29", 21.94- and 33.96", assigned to crystalline CuC12.2H20, in addition to those of the NaZSM-5 zeolite [Fig. l(c)]. It is of interest to note that the characteristic peaks assigned to crystalline CuCI2.2H2O disappear completely when the sample is treated in a micro- wave oven for 10 min, as given in Fig. 1(d).The disappearance of the XRD peaks of crystalline CuClz.2H,0 in CuCl,. 2H20-NaZSM-5 can be explained by the high dispersion of CuC1,.2H20 in the NaZSM-5 zeolite channels, where the CuCl2.2H20 no longer exists in the crystalline ~tate.~,~',~~ Increasing the CuC12-2H,0 mass loading in NaZSM-5 zeolite to 0.50 (Cu:Al=7.6), we observed that the XRD peaks of NaZSM-5 maintained their positions, and we could not observe the XRD peaks of crystalline CuCl,.2H20, as shown in Fig.l(e)-(h). With a further increase in CuC12.2H20 mass loading in NaZSM-5 zeolite to 0.60-0.70 (Cu: A1 =9.1-10.6), the characteristic peaks assigned to crystalline CuC12-2H20 appear [Fig. l(i)-(l)]. Fig. 2 shows the XRD patterns of NaY zeolite mixed with CuC1,-2H20 under microwave conditions. The results demon- strate that CuC12.2H20 is highly dispersed in the pores of NaY zeolite with a CuCl2.2HZO mass loading of 0-0.60 (CU:A1=1.0). In contrast to those samples prepared from the copper ion-exchanged method, Cu/NaZSM-5 prepared from the microwave technique exhibits the following features: (i) the -10 20 30 10 20 30 10 20 30 20ldegrees Fig.1 XRD patterns of NaZSM-5 and CuC12.2H20 under various conditions: (a)NaZSM-5; (b) NaZSM-5 in microwave oven for 60 min; (c)mechanical mixture of CuC1,.2H20 and NaZSM-5 with CuC12.2H20 loading of 0.10 g g-' (Cu:Al= 1.5); (d)sample (c) in microwave oven for 10 min; (e)mechanical mixture of CuC12.2H20 and NaZSM-5 with CuC12.2H20 loading of 0.20 g g-' (Cu :A1 =3.0) in microwave oven for 10 min; (f)mechanical mixture of CuC12.2H20 and NaZSM-5 with CuCl,.2H20 loading of 0.30 g g-' (Cu: A1 =4.5) in microwave oven for 10 min;(g) mechanical mixture of CuC12.2H20 and NaZSM-5 with CuC1,*2H20 loading of 0.40 g g-' (Cu :A1=6.0) in microwave oven for 10 min; (h) mechanical mixture of CuC12-2H20 and NaZSM-5 with CuC12.2H20 loading of 0.50 g g-' (Cu :A1 =7.5) in microwave oven for 10 min; (i) mechanical mixture of CuCI2.2H2O and NaZSM-5 with CuCl,.2H20 loading of 0.60 g g-' (Cu: Al=9.0); (j)after i, the sample in microwave oven for 20 min; (k)mechanical mixture of CuCl,.2H20 and NaZSM-5 with CuC1,.2H20 loading of 0.70 g g -' (Cu :A1 = 10.5); (1) sample (k)in microwave oven for 20 min (V,characteristic peaks of CuC12-2H,0) J.MATER. CHEM., 1994, VOL. 4 -10 20 30 10 20 3 2eldegrees Fig.2 XRD patterns of NaY and CuC12.2H20 under various con- ditions: (a)Nay; (b)NaY in microwave oven for 60 min; (c) mechanical mixture of CuC12-2H20 and NaY with CuC12-2H20 loading of 0.20 g g-' (Cu: Al= 0.34); (d) sample (c) in microwave oven for 10min; (e) mechanical mixture of CuCl,.2H20 and NaY with CuC1,.2H20 loading of 0.40 g g-' (Cu: A1 =0.67) in microwave oven for 10min; (f)mechanical mixture of CuC12.2H20 and NaY with CuCl2.2H20 loading of 0.60 g g-' (Cu :Al= 1.0) in microwave oven for 10min; (g) mechanical mixture of CuC12.2H20 and NaY with CuC12.2H20 loading of 0.80 g g-' (Cu: Al= 1.34); (h) sample (9) in microwave oven for 20 min (V,characteristic peaks of CuC12*2H20) dispersion loading of CuC1, in NaZSM-5 is very large; we can prepare the CuC12.2H,0-NaZSM-5 with CuC1,-2H2O loading up to 0.50-0.6Og g-' (Cu:Al=7.6-9.1 g g-'), the higher Cu loading in zeolites may produce a better catalyst for NO, decomposition; (ii) it takes a very short time; generally, the dispersion of CuC12-2H20 in zeolites takes only 10 min; (iii) the preparation of samples is very simple without stirring in solution, drying and calcination steps.Using the microwave technique, we have recently prepared the series of samples: CuC1,-silicalite-I, AuC1,-NaZSM-5, AuC1,-Nay, RuC1,-Nay, NiC1,-NaZSM-5 and Li,S04-AlPO,-11, and it is found that metal salts such as CuCl,, AuCl,, NiCl,, RuC1, and Li,S04 can be highly dispersed in the channels of various zeolites such as silicate-I, NaZSM-5, Beta, and AlPO,-11, which are well characterized by X-ray diffraction.,O In some conditions, the above-mentioned mate- rials exhibit some specific chemical properties.For example, the sample of AuCl,-NaY prepared from highly dispersed AuC1, in NaY zeolite under microwave conditions is very active for the decomposition of NO,, and even at room temperature partial CO and NO can be converted into CO, and N2 over an AuC1,-NaY The Li2S04-AlP04- 1 1 sample prepared from highly dispersed Li2S0, in AlPO, zeolite under microwave conditions has a much higher electronic conductivity than does Li2S0,.42 More recently, we have studied the rare-earth ion (Ce3+, Eu3+ and Sm3+) exchanged zeolites (Beta, NaY and NaX) in aqueous solution under microwave condition^,^^ and it is found that the rate of ion-exchange of zeolites under micro- wave conditions is ca. 60 times that of the sample without using the microwave.Generally, a complete exchange of Ce3+ with Na-Beta zeolite takes only 8min under microwave conditions. Comparatively, the same Ce3 +-exchanged content in Na-Beta zeolite takes at least 8 h. Hexane Isotherms Fig. 3 shows the hexane isotherms on various samples. It is clear that all samples exhibit Langmuir-type isotherms.26 For NaZSM-5 and CuZSM-5, the hexane isotherms are the same, indicating that NaZSM-5 and CuZSM-5 have the same channels and surface areas. For a mechanical mixture of CuC1,.2H2O with NaZSM-5, the shape of the hexane iso- therm is the same as those of NaZSM-5 and CuZSM-5, but the adsorption amount of hexane is reduced, which is in good agreement with the theoretical value for the CuC12.2H20-NaZSM-5 sample estimated by the isotherm of NaZSM-5 [Fig.3(a)], where NaZSM-5:(CuC1,.2H20 + NaZSM-5)=0.91 and only NaZSM-5 can adsorb hexane. It is interesting to note that hexane adsorption on the sample (CuC1,.2H20 :NaZSM-5 =0.10 g g-I), treated in a microwave oven for lOmin, requires a higher hexane pressure to reach saturated adsorption [Fig. 3(c)], compared with those on NaZSM-5, CuZSM-5 and the mechanical mixture of CuC12.2H20 with NaZSM-5 without the treatment of micro-wave oven. This phenomenon may be interpreted by the different arrangement of channels in various samples. The microwave effect for the CuC12.2H,0-NaZSM-5 sample may result in the high dispersion of CuC1, into channels of NaZSM-5, leading to a change in channel shape in the zeolite, '1o! 0 0.1 0.2 0.3 0.4 0.5 PIP0 Fig.3 Hexane isotherms on various samples: (u)NaZSM-5 treated in microwave oven for 60min; (b) CuZSM-5 exchanged by CuC1, aqueous solution with NaZSM-5; (c) mechanical mixture of CuC12.2H20 with NaZSM-5 (weight ratio of 0.10 g g-', Cu :A1 = 1.5); (d) mechanical mixture of CuC1,-2H20 with NaZSM-5 (weight ratio of 0.10 g g-', Cu: Al= 1.5) in microwave oven for 10 min; (e)mcchan-ical mixture of CuC1,-2H20 with NaZSM-5 (weight ratio of 0.30 g g-',Cu :A1=4.5) in microwave oven for 10 min which strongly influences the adsorption of hexane on the samples. Accordingly, the higher the copper loading on NaZSM-5, the larger the change in hexane isotherm. In fact, the sample with mass ratio CuC12.2H,0 :NaZSM-5 =0.30 exhibits a lower adsorption amount and a higher adsorption pressure for saturated hexane adsorption, in contrast to those of the other samples, as shown in Fig.3(e). The CuCl,-ZSM-5 sample with CuC1,.2H20 :NaZSM-5 =0.70 g g- (Cu :A1 = 10.5) shows a small adsorption capacity, suggesting that at the higher Cu loading, the pores are either completely filled, or the pore windows are obstructed with residual material. IR Spectra of CO Adsorbed on Samples Fig.4 shows the IR spectra of CO adsorbed on CuZSM-5 and CuC1,-NaZSM-5 treated in the microwave oven. CuZSM-5 [Fig. 4(a)] exhibits bands at 2170 and 2156 cm-', which could possibly be assigned to Cu2+(CO) and Cu'(C0) species, respecti~ely.~~~ The CuC1,-NaZSM-5 sample also gives rise to bands at 2168 and 2156cm-', with intense CO adsorbed species, as shown in Fig. 4(b).This result indicates that the concentrations of Cu2+(CO) and Cu'(C0) complexes on CuC1,-NaZSM-5 is very high, compared with that on CuZSM-5. Comparatively, we can not observe the bands at 2180-2150 cm-' assigned to Cu"+(CO) (n= 1,2) for CO adsorption on the CuCl,.2H20-NaZSM-5 sample not treated in the microwave oven but pretreated by evacuation for 2 h at 473 K. The above results also indicate that CuCl, is highly dispersed in the channels of NaZSM-5 zeolite. Thermal Analysis Fig. 5 shows the curves of DTA for various samples. The sample of NaZSM-5 shows one peak at 361 K in the DTA curve, which is assigned to the desorption of water adsorbed on NaZSM-5.The DTA curve of CuC12.2H,0 shows two peaks, at 400 and 773 K [Fig. 5(b)],which are attributed to the dehydration of CuC1,-2H20 and the melting point of CuCI,, respectively. The mechanical mixture of CuCI2.2H,O with NaZSM-5 (weight ratio, 0.10 g g-', Cu: Al= 1.5) gives 0.25AI (b ) -2200 2025 1850 1E 5 wavenumbedcm-' Fig.4 Differential IR spectra between CO adsorbed on the sample and the background of the sample: (a)CuZSM-5 exchanged by CuCl, aqueous solution with NaZSM-5; (b) mechanical mixture of CuCI,-2H20 with NaZSM-5 (weight ratio of 0.30 g g-', Cu :A1 =4.5) in microwave oven for 10 min J. MATER. CHEM., 1994, VOL. 4 400 I I I I 383 523 663 803 TIK Fig.5 DTA curves of (a) NaZSM-5 in microwave oven for 10min, (b)CuC1,.2H20, (c)mechanical mixture of CuCl2.2Hz0 and NaZSM-5 with weight ratio of CuC1,.2H20 :NaZSM-5 of 0.10 g g-' (Cu :A1= lS), (d) mechanical mixture of CuC12.2H,0 and NaZSM-5 with weight ratio of CuC12.2H20:NaZSM-5 of 0.10 g g-' (Cu:Al= lS), followed by treatment in microwave oven for 10 min, (e) mechanical mixture of CuC12.2H20 and NaZSM-5 with weight ratio of CuC1,.2H20 :NaZSM-5 at 0.30 g g-' (Cu :A1 =4.5), followed by treatment in microwave oven for lOmin, (f)mechanical mixture of CuCl,*2H20 and NaZSM-5 with weight ratio of CuC1,.2H2O :NaZSM-5 at 0.60 g g-' (Cu :A1=9.0), followed by treatment in microwave oven for 20 min two strong peaks at 390 and 603 K, as shown in Fig.5(c). The peak at 390K is very similar to the peak at 400K assigned to the dehydration of CuC1,.2H20 in Fig. 5(b),and thus we assigned this peak to the dehydration of the CuC1,.2H2O-NaZSM-5. The peak at 603 K may be due to the 'monolayer' dispersion of CuC1, in the NaZSM-5, in the temperature range 573-723 K. Similar phenomena have been studied extensively by Xie et aL6 It is very interesting to find that, after the reaction of CuC1,.2H2O-NaZSM-5 in a micro- wave oven for 10 min, the sample profile exhibits only a peak at 380 K assigned to the dehydration of the sample, the peak at 603 K in Fig. 5(c) and the peak at 773 K in Fig. 5(b) completely disappeared. These results may be interpreted by the high dispersion of CuC1,-2H2O in NaZSM-5 zeolite under microwave conditions.6 When the copper loading in NaZSM-5 was increased to give a weight ratio of CuC1,.2H2O :NaZSM-5 =0.30 g g -'(Cu :A1 =4.5) treated in the microwave oven, the sample DTA curve still exhibited one main peak at 400K.With further increase in CuC12.2H,0 loading in NaZSM-5 up to 0.60 g g-' (Cu :A1 =9.0), followed by treatment in the microwave oven for 20min, the sample profile gave the peaks at 400 and 770 K. The peak at 400 K is assigned to the dehydration of the sample, and the other peak, at 770K, is assigned to the melting point of CuC1, because of the residual crystalline CuCl, in CuC1,.2H20-NaZSM-5. The above phenomena are the same as those for CuC1,-zeolites prepared via 'monolayer disper- J.MATER. CHEM., 1994, VOL. 4 739 sion' of CuCl,-NaZSM-5 by heating a mixture of CuC1, and NaZSM-5 for 12 h at 623 K and demonstrate that the CuCl, is highly dispersed in the channels of NaZSM-5, and that the saturated amount for CuC1,.2H20 dispersion in NaZSM-5 is a weight ratio of CuC1,.2H20-NaZSM-5 of ca. 0.50 g g-'. 2 3 4 5 G. Poncelet, P. Grange, and P. A. Jacobs, in Preparation of Catalysts 111, Elsevier, Amsterdam, 1983. H. C. Yao, Y. F. Yu Yao and K. Otto, J. Catal., 1979,%, 21. G. Y. Lee and J. C. Zhao, Petrochem. Technol. (China), 1987, 16, 266. T. Mikae, K. Sekizawa, T. Hironaka, M. Nakano, S. Fujii and Y. Tsutsumt, New Develop. Zeolite Sci. Technol., Proc. 7th Znt. Conclusions Zeolite Con$, Kodansha, Tokyo, 1986, p. 747. Y.-C. Xie and Y.-Q.Tang, Adv. Catal., 1990,37, 1. The important conclusions of this study may be summarized as follows. (a) After reaction of CuCI2.2H,O with zeolites in a microwave oven for 10-20 min at ambient temperature, the samples of CuCl,-zeolites (CuC12.2H,0 :NaZSM-5 = 0.1-0.50 g g-'; CuCl,-2H20:NaY =0.1-0.60 g g-') showed only those peaks assigned to the zeolite, and the characteristic peaks of CuCl2-2H,O disappeared completely, suggesting that the CuC1, is highly dispersed on the channel surfaces of the zeolites under microwave conditions. Using the microwave technique, some samples having catalytic activities could be prepared, such as CuC1,-silicalite-I, AuC1,-Nay, 10 11 12 13 14 15 J. M. J. G. Lipsch and G. C. A. Schuit, J. Catal., 1969,15174. F. E. Mossoth, J.Catal., 1973,30,204. N. Giordano, J. C. J. Bart, A. Vaghi, A. Castellan and G. Martinofti, J. Catal., 1975,36,81. J. Sonnemans and P. Mars, J. Catal., 1973,31,203. M. Iwamoto, S. Yokoo, K. Sakai and S. Kagawa, J. C hem. SOC., Faraday Trans. I, 1981,77,1629. M. Iwamoto, H. Yahiro, Y. Mine and S. Kagawa, Cirem. Lett., 1989,213. M. Iwamoto, H. Yahiro, K. Tanada, N. Mizuno, Y. Mine and S. Kagawa, J. Phys. Chem., 1991,95,3727. Y. Li and W. K. Hall, J. Phys. Chem., 1990,94,6415. Y. Li and W. K. Hall, J. Catal., 1991,129,202. AuC1,-ZSM-5, RuC1,-Nay, NiC12-ZSM-5 and Li2S04-AlP04-11. In these cases, CuCI,, AuCI,, NiCl,, RuCl, and Li,SO, could be highly dispersed in the pores/channels of the molecular sieves silicalite-I, ZSM-5, Beta and AIP04-11, respectively. Therefore, it is suggested that the reaction of some inorganic salts mixed with zeolites under microwave conditions may be a new route for the dispersion of some inorganic salts onto the channel surfaces of zeolite crystals.(b) Compared with the ion-exchanged methods, the reaction of CuCI2.2H,O mechanically mixed with zeolites such as NaZSM-5 under microwave conditions exhibits the following features: (i) the dispersion loading of CuCl, in NaZSM-5 is very large; highly dispersed CuC1,-2H20-NaZSM-5 can be prepared with Cu :A1=0-9.0; comparatively, the maximum Cu:A1 of CuZSM-5 prepared from copper ion-exchange is ca. 0.5-0.75; (ii) it takes a very short time; generally, the high dispersion of CuC12.2H20 in NaZSM-5 zeolite takes only 10 min; (iii) the preparation of samples is very simple, without stirring in solution, drying and calcination; (iv) in a microwave oven, CuC1,.2H20 can disperse easily in silicalite-I zeolite which does not have ion-exchange capability. The Cu-silicalite-I sample cannot be prepared by the ion-exchange method. (c) Hexane isotherms of CuCl,-NaZSM-5 treated in a microwave oven exhibit a higher adsorption pressure to reach saturated adsorption of hexane, compared with those of NaZSM-5 and a mechanical mixture of NaZSM-5 and CuC1,-2H2O without treatment in the microwave oven, which 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 Y.Li and J. N. Armor, Appl. Catal., 1991,76,21. M. Shelef, Catal. Lett., 1992, 15,305. W. K. Hall and J. Valyon, Catal. Lett., 1992,15, 311. Y. Li and J. N. Armor, US Pat., 1992,5149512.C. H. Bartholomew, R. Gopalakrishna, J. Davidson, P Stafford and W. C. Hechker, 13th North American Meeting of the Catalysis Society, PA-47, Pittsburgh, May 2-6, 1993. D. W. Breck, in Zeolite Molecular Sieves, Wiley, New York, 1974. G. D. Stuckey and F. G. Dwyer, in lntrazeolite Chemistry, ACS Symposium Series 218, American Chemical Society, Washington D.C., 1983. J. A. 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