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Epoxidation of cyclic-olefins over carbon template mesoporous TS-1
Microporous and Mesoporous Materials 141 (2011) 2–7
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Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso
Epoxidation of cyclic-olefins over carbon template mesoporous TS-1 q Dae-Yong Ok, Nanzhe Jiang, Eko Adi Prasetyanto, Hailian Jin, Sang-Eon Park ⇑ Laboratory of Nano-Green Catalysis and Nano Center for Fine Chemicals Fusion Technology, Department of Chemistry, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, South Korea
a r t i c l e
i n f o
Article history: Received 9 April 2010 Received in revised form 6 September 2010 Accepted 22 December 2010 Available online 30 December 2010 Keywords: Mesoporous TS-1 Carbon template Cyclo-olefins oxidation Hydrogen peroxide
a b s t r a c t Mesoporous TS-1 was prepared by varying the amount of carbon particles using as a hard template average size 12 nm under the microwave irradiation. The catalytic activity of carbon templated mesoporous TS-1 (C-meso-TS-1) was ratified by epoxidation of various cyclic olefins and the catalytic activity was compared with TS-1 synthesized by hydrothermal method. The activity of mesoporous TS-1 increased with increasing the carbon content. Mesoporous TS-1 showed higher activity than the microporous TS-1. Ó 2011 Elsevier Inc. All rights reserved.
1. Introduction TS-1 zeolite is Ti substituted silicalite-1 which belongs to the MFI structural group. Over the last decades, TS-1 zeolite known to have an excellent catalytic properties for selective oxidation of number of organic substrates, using hydrogen peroxide as an oxidant under mild condition [1,2]. TS-1 has also been used in several types of oxidation reactions including hydroxylation, epoxidation, ammoxidation and aromatic oxidation. Moreover, hydrogen peroxide used as a green oxidant in these reactions due to the fact that by-product is only water [3]. In alkenes epoxidation, many studies have been done to enhance the epoxide selectivity. Epoxides play an important role both in organic synthesis and pharmaceuticals. TS-1 is being used commercially for the production of catechol and hydroquinone from phenol, and also for the synthesis of cyclohexanone oxime from cyclohexanone [4,5]. The successful applications of TS-1 as a catalyst arise due to unique synthetic procedure by which the pore diameter can control topology, and also the nature, concentration of active sites. More than eight types of zeolite have been used in oil refining process. The number will be more if it counted especially in the field of catalysis for production of bulk chemical and fine chemicals. However, main drawback is that the pore blockage by coking, reduced yields and selectivity which cause the slow diffusion rate of reactants and products in microporous channel structures (typically smaller than 1.2 nm) are serious problems that routinely arise in q Presented at the International Symposium on Zeolites and Microporous Crystals (ZMPC2009), held at Waseda University in Tokyo, Japan, August 3–7, 2009. ⇑ Corresponding author. Tel.: +82 32 860 7675; fax: +82 32 872 8670. E-mail address: [email protected] (S.-E. Park).
1387-1811/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2010.12.031
catalytic applications of zeolites [6,7]. The inclusion of broad pores may help to overcome these problems [8]. The increased diffusion limitation of zeolites is responsible for significant decrease of the undesired product selectivity due to the increased interaction time between the active sites and reactants in zeolite pores [9]. This fact has stimulated research of zeolites with larger pores and amorphous mesoporous titanium containing materials [10]. Mesoporous materials such as MCM-41 family and SBA series have uniform pore like zeolites but with a diameter greater than 20 Å. The initial work from Mobil R&D Corp. demonstrated that cationic surfactants, such as cetyltrimethylammonium cation (CTMA+), can act equivalently like the organic structure directing agents of zeolites which can generate aluminosilicate and other metal oxide materials with uniform channels in the mesoporous region [11,12]. Although, improvement of mesoporous materials suggest a new opportunity, the relatively weak activity and poor hydrothermal properties of mesoporous materials have resulted limitations in the practical applications. In view of this, mesoporous zeolites which can provide several benefits which could potentially improve the efficiency of zeolite in catalysis such as the increase the external surface area, low limitations on transport in zeolites channels and a high hydrothermal stability are highly demanded. Moreover, the development of mesopores can favor the production of various unexplored products those may be in demand for numerous applications. To develop mesoporosity in zeolite single crystals increase the accessibility to the internal surface, several methods research such as dealumination, desilication and other chemical treatment for forming defect site, a hard templating method have been introduced [13–16]. Using carbon materials as hard template is one of the most reliable methods to synthesize mesoporous zeolites with fully crystalline walls. This kind of
D.-Y. Ok et al. / Microporous and Mesoporous Materials 141 (2011) 2–7
mesoporous zeolite have been prepared by crystallizing in the presence of carbon materials such as carbon black [10,13–21], mesoporous carbon [22,23], colloid imprinted carbon [24], and carbon aero gel [25]. It was found that the microwave process is especially useful for the synthesizing of porous crystalline materials. Microwave heating was conceived about 50 years ago and it is a relatively new in the field of synthesis nano materials [26]. A significant increase in microwave processing research began in the late 1980s for ceramics and polymers. Especially, researchers of Mobil Co. studied the application of microwave in the nanoporous materials in 1988. So far, there are numerous research groups worldwide that are applying microwave energy to different types of materials and products. Here we are reporting the preparation of mesoporous TS-1 with different amount of carbon as a hard template under microwave
7000
Intensity(a. u.)
6000 5000 (d)
4000 3000
(c)
2000 (b)
1000 (a)
0 10
20
30
40
50
60
2θ degree Fig. 1. High angle XRD patterns of C (a) 10 wt%, (b) 20 wt%, (c) 30 wt%, and (d) 40 wt% of mesoporous TS-1 prepared by microwave synthesis.
3
irradiation. Nanosized carbon materials as a template during the zeolite crystallization were utilized to make a mesoporous TS-1. Here we also described the epoxidation of different size of cyclicolefins by carbon templated mesoporous TS-1. In this work, we have prepared carbon template mesopoorus TS-1 in order to widen its catalytic application for relatively larger size olefin such as cyclohexene, cyclooctene, and cyclododecene. 2. Experimental 2.1. Preparation of carbon template mesoporous TS-1 TS-1 zeolite (Si/Ti = 100) was synthesized using tetraethylortho silicate (TEOS, 95%, Aldrich) as the silica source and titanium tetra isopropoxide (Ti(OPr)4, 97%, Aldrich) as the Ti source. Moreover, tetrapropyl ammonium hydroxide (TPAOH, TCI, 25%) was used as the structure-directing agent. The composition of the final gel with Si/Ti was: SiO2:TiO2:TPA-OH:H2O:IPA = 1:0.01:0.5:23.33:1.13 In typical synthesis, 48 g TPA-OH was mixed in 48 g of distilled water and appropriate amount of carbon (Carbon Black Pearl 2000 – ranging from 10 to 40 wt% of C/Si source) was added and allowed to stir for 12 h. TIP (0.328 g) was dissolved in 8 g of isopropyl alcohol (IPA, 99%, DC chemical) and 24 g TEOS was added and allowed to stir for 12 h then added to the above mixture. Finally, the whole mixture was vigorously stirred for 4 h. After stirring it was put into a microwave oven equipped with a Teflon autoclave, and was irradiated at 80 °C for 30 min under 1200 W microwave power after that increasing temperature at 165 °C under 1200 W holding 5 min and was maintained at 165 °C under 1200 W microwave power during 60 min. The resulting solid product was filtered, washed with deionized water; and dried in air at 60 °C for 12 h. To remove the organic template, the as-synthesized samples were calcined at 550 °C for 10 h in air. 2.2. Characterization of carbon templated mesoporous TS-1 Crystallinity and phase purity of this materials was determined by powder X-ray diffraction using a Rigaku diffractometer
Fig. 2. SEM images of (a) C 10 wt%, (b) C 20 wt%, (c) C 30 wt%, and (d) 40 wt% of mesoporous TS-1 prepared by microwave synthesis.
D.-Y. Ok et al. / Microporous and Mesoporous Materials 141 (2011) 2–7
2.3. Catalytic reaction Carbon template mesoporous TS-1 catalysts were dehydrated at 100 °C for 2 h. The catalytic epoxidation of cyclohexene, cyclooctene, and cyclododecene with hydrogen peroxide were carried out using EYELA ChemiStation Personal Organic Synthesizer. Each reactant was reacted with carbon templated mesoporous TS-1 with C 10, 20, 30, and 40 wt% as a hard template. Firstly, reaction mixture which contains 20 mmol of each olefin, mesitylene as standard material and methanol 20 ml as a solvent was prepared before temperature was reached to 72 °C. After temperature was reached to 72 °C, 50 mg catalysts and 10 mmol hydrogen peroxide was added to that vessel. The reaction products were collected at 1, 3, and 5 h and analyzed by gas chromatograph with flame ionization detector and HP-5 capillary column. 2.4. Result and discussion XRD patterns of carbon templated mesoporous TS-1 synthesized by microwave irradiation method was shown in Fig. 1. This pattern was obtained after the zeolite synthesis, followed by combustion of the carbon black pearl material by calcinations. In Fig. 1, it is seen that all samples contain exclusively highly crystalline MFI structure, and with the increase the amount of carbon in the synthetic mixture, the high angle XRD pattern showed more increased peaks due to the presence of carbon particle which might play a crucial role on microwave absorption sites. But the low angle XRD peak intensity of those mesoporous TS-1 was not observed due to the freely dispersed carbon particles during synthesizing.
The scanning electron microscopy was used to observe the morphologies of mesoporous TS-1 synthesized by microwave heating. Fig. 2 shows the SEM images of each mesoporous TS-1 crystal. SEM micrographs of carbon templated mesoporous TS-1 together with high angle XRD pattern proved that the crystal size increased by increasing the amount of the carbon contents. In order to develop the large mesoporous zeolite crystals rather than small zeolite crystals, it is essential that an excess of sufficient carbon matrix required which allows growth to proceed through the pore system [17]. So we suggest that carbon particle played an important role as microwave absorber to develop the crystallinity. In Fig. 3, the transmission electron microscopy images clearly showed that the well-shaped crystals and the presence of mesopores in typical TS-1 crystals, resulting in some inter-particle voids by combustion of carbon template were displayed. It is seen that relatively large and well-shaped crystals are obtained. The significant mesoporosity of individual TS-1 crystals is indicated in micrograph. The mesopores were clearly observed as a well-dispersed bright spots throughout the entire zeolite crystal. Fig. 4 shows the nitrogen adsorption and desorption isotherms of mesoporous TS-1 zeolites synthesized by microwave method
300 280 3
(0.8–6° in 2h) and employing Cu Ka radiation (k = 0.1547 nm). Scanning electron microscopy (SEM) was performed on a JEOL 630-F microscope instrument. Transmission electron microscopy (TEM) images were recorded with a JEOL JEM-3011 electron microscope operated at 200 kV and equipped with CCD camera. N2 adsorption experiments were performed with a Micromeritics ASAP 2020 surface area analyzer. The samples were out gassed at 300 °C prior to the measurement. The surface area was calculated by using the BET method and the pore parameters calculated on the basis of the N2 adsorption–desorption isotherms. Raman spectra was performed on a 45-MRM-302-220 (Multimode HeCd Laser 30 mW, 325 nm, unpolarized, 220 V) for confirm the incorporating of Ti species into the zeolite structure.
Amount adsorbed (cm /g)
4
(d)
260 240 (c)
220 200
(b)
180
(a)
160 (e)
140 120 100 80 0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0) Fig. 4. N2 adsorption and desorption isotherms of C (a) 10 wt%, (b) 20 wt%, (c) 30 wt%, and (d) 40 wt% of mesoporous TS-1 prepared by microwave synthesis and (e) microporous TS-1.
Fig. 3. TEM images of (a) C 20 wt%, (b) C 30 wt%, and (c) 40 wt% of mesoporous TS-1 prepared by microwave synthesis.
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D.-Y. Ok et al. / Microporous and Mesoporous Materials 141 (2011) 2–7
with carbon content in the synthesis precursor gel from 10 to 40 wt% after combustion of the carbon. The isotherms of all samples contain a hysteresis loop at relative pressures lower than P/P0 = 0.2 and higher than P/P0 = 0.4. This hysteresis could be separated with large pore, milli mesopore, and super micropore. The low pressure hysteresis loop at round P/P0 = 0.2 suggest that
0.005
synthesis steaming caused developing of a significant amorphous phase and the redistribution of the crystalline phase to smaller pore sizes [27,28]. The amounts of nitrogen adsorbed by the mesoporous TS-1 depended on the amount of carbon that was added into the synthesis mixture. The pore size distribution of mesoporous TS-1 was shown in Fig. 5. All the samples possess mesopores with sizes in the range of 10–20 nm widths. This diameter matches with the Carbon Black pearl 2000 particles having an average particle size of 12 nm occupied these positions before combustion
22 20
0.003
(d)
Cyclohexene
18
0.002 (a) (b) (c)
0.001
16
Conversion / %
Pore Volume (cm3/g)
0.004
(d)
14
5
10
15
20
25
30
35
40
45
50
55
(e)
10 8
(e)
0.000
(c) (b)
12
6
60
(a)
4
Pore Diameter (nm)
2
Fig. 5. Pore size distribution of C (a) 10 wt%, (b) 20 wt%, (c) 30 wt%, and (d) 40 wt% of mesoporous TS-1 prepared by microwave synthesis and (e) microporous TS-1.
50
100
150
200
250
300
Reaction time (min) 10
Cyclooctene
C 10 wt% TS-1 MW C 20 wt% TS-1 MW C 30 wt% TS-1 MW C 40 wt% TS-1 MW Microporous TS-1
SBET (m2/g)b
SMicro (m2/g)b
SMeso (m2/g)b
VMicro (cm3/g)c
VMeso (cm3/g)c
422 416 360 382 348
283 172 122 110 203
139 242 239 272 145
0.12 0.09 0.06 0.06 0.14
0.10 0.13 0.13 0.14 0.08
8
Conversion / %
Catalyst
a
(d)
9
Table 1 Properties of C 10, 20, 30, and 40 wt% of mesoporous TS-1 prepared by microwave synthesis and microporous TS-1.
7
(c) (b)
6
(a)
5 (e) 4 3
a
The numbers 10–40 and C represents the weight ratio of C to Si, and Carbon Black pearl 2000, respectively. And microporous TS-1 represents conventional TS-1 without adding C. b Calculated by BET method. c Calculated by BJH method (desorption).
2 1 50
100
150
200
250
300
Reaction time (min) 6.0
6
Cyclododecene
(d)
5.5 5.0
4
Conversion / %
Intensity(a. u.)
5
(b)
3
2
(a)
4.5
(c)
4.0 3.5 3.0
(b)
2.5 2.0
(a) (e)
1.5 1.0
1
0 900
0.5 50 1000
1100
1200
-1
Raman shift (cm ) Fig. 6. Raman spectra of (a) C 20 wt% and (b) 40 wt% of mesoporous TS-1.
100
150
200
250
300
Reaction time (min) Fig. 7. Epoxidation of cyclohexene, cyclooctene, and cyclododecene over C (a) 10 wt%, (b) 20 wt%, (c) 30 wt%, and (d) 40 wt% mesoporous TS-1 prepared by microwave synthesis and (e) microporous TS-1.
6
D.-Y. Ok et al. / Microporous and Mesoporous Materials 141 (2011) 2–7
Table 2 Epoxidation of (a) cyclohexene, (b) cyclooctene, and (c) cyclododecene over C 10, 20, 30, and 40 wt% mesoporous TS-1 prepared by microwave synthesis and microporous TS-1. Catalyst
Conversion (%)
(a) Epoxidation of cyclohexene C 10 wt% TS-1 MW 5.1 C 20 wt% TS-1 MW 12 C 30 wt% TS-1 MW 12.3 C 40 wt% TS-1 MW 21.1 Microporous TS-1 11.1 (b) Epoxidation of cyclooctene Catalyst
C 10 wt% TS-1 MW C 20 wt% TS-1 MW C 30 wt% TS-1 MW C 40 wt% TS-1 MW Microporous TS-1
Product distribution (%)
Yield of epoxide (%)
Epoxide
1,2-Cyclohexandiol
2-Cyclohexene-1-one
2-Cyclohexen-1-ol
Others
29 21 20 24 29
11 16 18.6 15.7 10.8
38 31.5 32.9 38.4 39
5.7 14.6 21.1 9.5 4.9
16.3 16.9 7.4 12.4 16.3
Conversion (%)
Product distribution (%)
1.5 1.5 2.5 5.1 3.2
Yield of epoxide (%)
Epoxide
2-Cyclooctene-1-one
Others
5.9 6.8 7.4 9.3 4.5
46.5 80.1 83.5 82 50
17.8 6.5 6.5 5.8 15.9
35.7 13.4 10 12.2 34.1
2.7 5.4 6.2 7.6 2.3
1.5 2.7 4.2 5.7 1.3
69 54 47 41 55
21.5 32 39 46.3 34.9
1.0 1.5 2.0 2.3 0.7
(c) Epoxidation of cyclododecene 2-Cyclododecene-1-one C 10wt% TS-1 MW C 20wt% TS-1 MW C 30wt% TS-1 MW C 40wt% TS-1 MW Microporous TS-1
9.5 14 14 12.7 10.1
Reaction condition: 50 mg catalyst was activated @ 100 °C for 2 h, temperature 70 °C, reaction time 5 h, cycloolefins:H2O2 (30 wt%) = 20:10 mmol, methanol 20 ml as a solvent.
at 550 °C. Broader peak around 30 nm was developed at C 40 wt% mesoporous TS-1 than other C 10, 20, and 30 wt% templated mesoporous TS-1. The physical properties of the mesoporous TS-1 synthesized with different carbon content are displayed in Table 1. BET surface area of all samples has similar value of high surface range from 300 to 400 m2/g that were developed by carbon templating method. The mesopore surface area of carbon templated mesoporous TS-1 prepared by microwave synthesis increased from 139 to 272 m2/g, in parallel micropore pore volume decreased from 0.12 to 0.06 cm3/g (Table 1). It apparently indicated that the mesopore of the carbon templated mesoporous TS-1 materials prepared by microwave synthesis were well-developed in TS-1 zeolite crystal with the amount of carbon. And the pore volume of carbon template mesoporous TS-1 is getting bigger with the increase of carbon adding due to the aggregation of carbon particle each other. The transition metal ions and the coordination state of Ti species substituted in the framework of the mesoporous TS-1 catalyst were identified by UV-Raman spectroscopy. Since most transition metal ions doped in zeolites or mesoporous zeotypes give a charge-transfer transition in the UV or near UV region, the resonance Raman effect can selectively enhance Raman bands that are associated with framework transition metals in framework sites while keeping the other Raman bands unchanged. Thus, it helps to identify the related species [29,30]. UV-Raman spectra of 20 and 40 wt% carbon templated mesoporous TS-1 are shown as Fig. 6. For these samples, Raman band at 970, 1110, and 1150 cm 1. While the band at 970 cm 1 assigned to the surface silanol groups. The UV-Raman spectra clearly shows band at 1110 cm 1 may be assigned as framework titanium species with tetrahedral coordination (Ti–O–Ti). The catalytic activity of these materials was tested for the epoxidation of cyclic-olefins to produce the epoxide at 70 °C using aqueous hydrogen peroxide as an oxidant. TS-1 has redox property that was contributed by tetrahedrally incorporated titanium species in the zeolite framework [31]. The catalytic epoxidation reaction of cyclohexene, cyclooctene, and cyclododecene was shown in
the Fig. 7 and Table 2. The selectivity towards the corresponding epoxides was also described in Table 2. The catalytic activities of five samples are evaluated by plotting the conversion as a function of time. Interestingly, in the case of cyclohexene epoxidation reaction could not observe any specific difference of the catalytic activity between carbon templated mesoporous TS-1 synthesized by microwave method and conventional TS-1 synthesized by hydrothermal method, the reason may be due to the small size of reactant that could not be limited by intra-crystalline diffusion and hence not dependent on whether microporous zeolite crystal or mesopore. So it showed similar catalytic activities with other carbon template mesoporous TS-1. In comparison, both cyclooctene and cyclododecene, every carbon templated mesoporous TS-1 synthesized by microwave has more superior catalytic activities than microporous TS-1 synthesized by hydrothermal method. TS-1 synthesized by hydrothermal method shows lower activity than carbon template mesoporous TS-1, which is attributed to its smaller pore size, making it difficult for large size cycloolefins to interact with the active Ti atoms present within the pores. So those results indicate that carbon particles can enhance the catalytic activity of TS-1 by widening the active sites to interact with bulkier molecules.
3. Conclusion Carbon template mesoporous TS-1 having single-crystal shape was successfully prepared by using microwave synthesis. The amounts of larger mesopores were proportional to the amounts of carbon used as a hard template. Although carbon was added, excellent crystalline product was observed because of carbon play a major role as a microwave absorber to give better crystallinity of the product. Carbon template mesoporous TS-1 (MW) catalyst showed higher catalytic activity than typical microporous TS-1 prepared in hydrothermal conditions. Mesoporous TS-1 prepared by microwave synthesis with varying the amounts of carbon resulted the increase of catalytic activities compared to the amounts of
D.-Y. Ok et al. / Microporous and Mesoporous Materials 141 (2011) 2–7
larger mesoporosities. Epoxidation of cyclooctene and cyclododecene over carbon template mesoporous TS-1 showed the good shape-selectivities contrary to the epoxidation of cyclohexene. Acknowledgment This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MEST) (No. 2009-0083073). References [1] M. Taramasso, G. Perego, B. Notri, U.S. Patent 4 (1983) 501. [2] T. Tastumi, M. Nakanura, S. Negishi, H. Tominnaga, J. Chem. Soc., Chem. Commun. (1990) 476. [3] J.-W. Yoo, C.-W. Lee, J.-S. Chang, S.-E. Park, J. Ko, Catal. Lett. 66 (2000) 169. [4] B. Notari, Stud. Surf. Sci. Catal. 37 (1988) 413. [5] A. Thangaraj, S. Sivasanker, P. Ratnasamy, J. Catal. 137 (1992) 252. [6] G. Caeiro, R.H. Carvalho, X. Wang, M.A.N.D.A. Lemos, R. Lemos, M. Guisnet, F. Ramôa Ribeiro, J. Mol. Catal. A: Chem. 255 (2006) 131. [7] M.-O. Coppens, in: A. Cybulski, J.A. Moulijn (Eds.), Structured Catalysts and Reactors, second ed., CRC Press, New York, 2006. [8] E. Johannessen, G. Wang, M.-O. Coppens, Ind. Eng. Chem. Res. 46 (2007) 4245. [9] G.A. Eimer, I. Diaz, E. Sastre, S.G. Casuscelli, M.E. Crivello, E.R. Herrero, J. PerezPariente, Appl. Catal. A: General 343 (2008) 77. [10] I. Schmidt, A. Krogh, K. Wienberg, A. Carlsson, M. Brorson, C.J.H. Jacobsen, Chem. Commun. (2000) 2157.
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Contents lists available at ScienceDirect
Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso
Epoxidation of cyclic-olefins over carbon template mesoporous TS-1 q Dae-Yong Ok, Nanzhe Jiang, Eko Adi Prasetyanto, Hailian Jin, Sang-Eon Park ⇑ Laboratory of Nano-Green Catalysis and Nano Center for Fine Chemicals Fusion Technology, Department of Chemistry, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, South Korea
a r t i c l e
i n f o
Article history: Received 9 April 2010 Received in revised form 6 September 2010 Accepted 22 December 2010 Available online 30 December 2010 Keywords: Mesoporous TS-1 Carbon template Cyclo-olefins oxidation Hydrogen peroxide
a b s t r a c t Mesoporous TS-1 was prepared by varying the amount of carbon particles using as a hard template average size 12 nm under the microwave irradiation. The catalytic activity of carbon templated mesoporous TS-1 (C-meso-TS-1) was ratified by epoxidation of various cyclic olefins and the catalytic activity was compared with TS-1 synthesized by hydrothermal method. The activity of mesoporous TS-1 increased with increasing the carbon content. Mesoporous TS-1 showed higher activity than the microporous TS-1. Ó 2011 Elsevier Inc. All rights reserved.
1. Introduction TS-1 zeolite is Ti substituted silicalite-1 which belongs to the MFI structural group. Over the last decades, TS-1 zeolite known to have an excellent catalytic properties for selective oxidation of number of organic substrates, using hydrogen peroxide as an oxidant under mild condition [1,2]. TS-1 has also been used in several types of oxidation reactions including hydroxylation, epoxidation, ammoxidation and aromatic oxidation. Moreover, hydrogen peroxide used as a green oxidant in these reactions due to the fact that by-product is only water [3]. In alkenes epoxidation, many studies have been done to enhance the epoxide selectivity. Epoxides play an important role both in organic synthesis and pharmaceuticals. TS-1 is being used commercially for the production of catechol and hydroquinone from phenol, and also for the synthesis of cyclohexanone oxime from cyclohexanone [4,5]. The successful applications of TS-1 as a catalyst arise due to unique synthetic procedure by which the pore diameter can control topology, and also the nature, concentration of active sites. More than eight types of zeolite have been used in oil refining process. The number will be more if it counted especially in the field of catalysis for production of bulk chemical and fine chemicals. However, main drawback is that the pore blockage by coking, reduced yields and selectivity which cause the slow diffusion rate of reactants and products in microporous channel structures (typically smaller than 1.2 nm) are serious problems that routinely arise in q Presented at the International Symposium on Zeolites and Microporous Crystals (ZMPC2009), held at Waseda University in Tokyo, Japan, August 3–7, 2009. ⇑ Corresponding author. Tel.: +82 32 860 7675; fax: +82 32 872 8670. E-mail address: [email protected] (S.-E. Park).
1387-1811/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2010.12.031
catalytic applications of zeolites [6,7]. The inclusion of broad pores may help to overcome these problems [8]. The increased diffusion limitation of zeolites is responsible for significant decrease of the undesired product selectivity due to the increased interaction time between the active sites and reactants in zeolite pores [9]. This fact has stimulated research of zeolites with larger pores and amorphous mesoporous titanium containing materials [10]. Mesoporous materials such as MCM-41 family and SBA series have uniform pore like zeolites but with a diameter greater than 20 Å. The initial work from Mobil R&D Corp. demonstrated that cationic surfactants, such as cetyltrimethylammonium cation (CTMA+), can act equivalently like the organic structure directing agents of zeolites which can generate aluminosilicate and other metal oxide materials with uniform channels in the mesoporous region [11,12]. Although, improvement of mesoporous materials suggest a new opportunity, the relatively weak activity and poor hydrothermal properties of mesoporous materials have resulted limitations in the practical applications. In view of this, mesoporous zeolites which can provide several benefits which could potentially improve the efficiency of zeolite in catalysis such as the increase the external surface area, low limitations on transport in zeolites channels and a high hydrothermal stability are highly demanded. Moreover, the development of mesopores can favor the production of various unexplored products those may be in demand for numerous applications. To develop mesoporosity in zeolite single crystals increase the accessibility to the internal surface, several methods research such as dealumination, desilication and other chemical treatment for forming defect site, a hard templating method have been introduced [13–16]. Using carbon materials as hard template is one of the most reliable methods to synthesize mesoporous zeolites with fully crystalline walls. This kind of
D.-Y. Ok et al. / Microporous and Mesoporous Materials 141 (2011) 2–7
mesoporous zeolite have been prepared by crystallizing in the presence of carbon materials such as carbon black [10,13–21], mesoporous carbon [22,23], colloid imprinted carbon [24], and carbon aero gel [25]. It was found that the microwave process is especially useful for the synthesizing of porous crystalline materials. Microwave heating was conceived about 50 years ago and it is a relatively new in the field of synthesis nano materials [26]. A significant increase in microwave processing research began in the late 1980s for ceramics and polymers. Especially, researchers of Mobil Co. studied the application of microwave in the nanoporous materials in 1988. So far, there are numerous research groups worldwide that are applying microwave energy to different types of materials and products. Here we are reporting the preparation of mesoporous TS-1 with different amount of carbon as a hard template under microwave
7000
Intensity(a. u.)
6000 5000 (d)
4000 3000
(c)
2000 (b)
1000 (a)
0 10
20
30
40
50
60
2θ degree Fig. 1. High angle XRD patterns of C (a) 10 wt%, (b) 20 wt%, (c) 30 wt%, and (d) 40 wt% of mesoporous TS-1 prepared by microwave synthesis.
3
irradiation. Nanosized carbon materials as a template during the zeolite crystallization were utilized to make a mesoporous TS-1. Here we also described the epoxidation of different size of cyclicolefins by carbon templated mesoporous TS-1. In this work, we have prepared carbon template mesopoorus TS-1 in order to widen its catalytic application for relatively larger size olefin such as cyclohexene, cyclooctene, and cyclododecene. 2. Experimental 2.1. Preparation of carbon template mesoporous TS-1 TS-1 zeolite (Si/Ti = 100) was synthesized using tetraethylortho silicate (TEOS, 95%, Aldrich) as the silica source and titanium tetra isopropoxide (Ti(OPr)4, 97%, Aldrich) as the Ti source. Moreover, tetrapropyl ammonium hydroxide (TPAOH, TCI, 25%) was used as the structure-directing agent. The composition of the final gel with Si/Ti was: SiO2:TiO2:TPA-OH:H2O:IPA = 1:0.01:0.5:23.33:1.13 In typical synthesis, 48 g TPA-OH was mixed in 48 g of distilled water and appropriate amount of carbon (Carbon Black Pearl 2000 – ranging from 10 to 40 wt% of C/Si source) was added and allowed to stir for 12 h. TIP (0.328 g) was dissolved in 8 g of isopropyl alcohol (IPA, 99%, DC chemical) and 24 g TEOS was added and allowed to stir for 12 h then added to the above mixture. Finally, the whole mixture was vigorously stirred for 4 h. After stirring it was put into a microwave oven equipped with a Teflon autoclave, and was irradiated at 80 °C for 30 min under 1200 W microwave power after that increasing temperature at 165 °C under 1200 W holding 5 min and was maintained at 165 °C under 1200 W microwave power during 60 min. The resulting solid product was filtered, washed with deionized water; and dried in air at 60 °C for 12 h. To remove the organic template, the as-synthesized samples were calcined at 550 °C for 10 h in air. 2.2. Characterization of carbon templated mesoporous TS-1 Crystallinity and phase purity of this materials was determined by powder X-ray diffraction using a Rigaku diffractometer
Fig. 2. SEM images of (a) C 10 wt%, (b) C 20 wt%, (c) C 30 wt%, and (d) 40 wt% of mesoporous TS-1 prepared by microwave synthesis.
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2.3. Catalytic reaction Carbon template mesoporous TS-1 catalysts were dehydrated at 100 °C for 2 h. The catalytic epoxidation of cyclohexene, cyclooctene, and cyclododecene with hydrogen peroxide were carried out using EYELA ChemiStation Personal Organic Synthesizer. Each reactant was reacted with carbon templated mesoporous TS-1 with C 10, 20, 30, and 40 wt% as a hard template. Firstly, reaction mixture which contains 20 mmol of each olefin, mesitylene as standard material and methanol 20 ml as a solvent was prepared before temperature was reached to 72 °C. After temperature was reached to 72 °C, 50 mg catalysts and 10 mmol hydrogen peroxide was added to that vessel. The reaction products were collected at 1, 3, and 5 h and analyzed by gas chromatograph with flame ionization detector and HP-5 capillary column. 2.4. Result and discussion XRD patterns of carbon templated mesoporous TS-1 synthesized by microwave irradiation method was shown in Fig. 1. This pattern was obtained after the zeolite synthesis, followed by combustion of the carbon black pearl material by calcinations. In Fig. 1, it is seen that all samples contain exclusively highly crystalline MFI structure, and with the increase the amount of carbon in the synthetic mixture, the high angle XRD pattern showed more increased peaks due to the presence of carbon particle which might play a crucial role on microwave absorption sites. But the low angle XRD peak intensity of those mesoporous TS-1 was not observed due to the freely dispersed carbon particles during synthesizing.
The scanning electron microscopy was used to observe the morphologies of mesoporous TS-1 synthesized by microwave heating. Fig. 2 shows the SEM images of each mesoporous TS-1 crystal. SEM micrographs of carbon templated mesoporous TS-1 together with high angle XRD pattern proved that the crystal size increased by increasing the amount of the carbon contents. In order to develop the large mesoporous zeolite crystals rather than small zeolite crystals, it is essential that an excess of sufficient carbon matrix required which allows growth to proceed through the pore system [17]. So we suggest that carbon particle played an important role as microwave absorber to develop the crystallinity. In Fig. 3, the transmission electron microscopy images clearly showed that the well-shaped crystals and the presence of mesopores in typical TS-1 crystals, resulting in some inter-particle voids by combustion of carbon template were displayed. It is seen that relatively large and well-shaped crystals are obtained. The significant mesoporosity of individual TS-1 crystals is indicated in micrograph. The mesopores were clearly observed as a well-dispersed bright spots throughout the entire zeolite crystal. Fig. 4 shows the nitrogen adsorption and desorption isotherms of mesoporous TS-1 zeolites synthesized by microwave method
300 280 3
(0.8–6° in 2h) and employing Cu Ka radiation (k = 0.1547 nm). Scanning electron microscopy (SEM) was performed on a JEOL 630-F microscope instrument. Transmission electron microscopy (TEM) images were recorded with a JEOL JEM-3011 electron microscope operated at 200 kV and equipped with CCD camera. N2 adsorption experiments were performed with a Micromeritics ASAP 2020 surface area analyzer. The samples were out gassed at 300 °C prior to the measurement. The surface area was calculated by using the BET method and the pore parameters calculated on the basis of the N2 adsorption–desorption isotherms. Raman spectra was performed on a 45-MRM-302-220 (Multimode HeCd Laser 30 mW, 325 nm, unpolarized, 220 V) for confirm the incorporating of Ti species into the zeolite structure.
Amount adsorbed (cm /g)
4
(d)
260 240 (c)
220 200
(b)
180
(a)
160 (e)
140 120 100 80 0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0) Fig. 4. N2 adsorption and desorption isotherms of C (a) 10 wt%, (b) 20 wt%, (c) 30 wt%, and (d) 40 wt% of mesoporous TS-1 prepared by microwave synthesis and (e) microporous TS-1.
Fig. 3. TEM images of (a) C 20 wt%, (b) C 30 wt%, and (c) 40 wt% of mesoporous TS-1 prepared by microwave synthesis.
5
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with carbon content in the synthesis precursor gel from 10 to 40 wt% after combustion of the carbon. The isotherms of all samples contain a hysteresis loop at relative pressures lower than P/P0 = 0.2 and higher than P/P0 = 0.4. This hysteresis could be separated with large pore, milli mesopore, and super micropore. The low pressure hysteresis loop at round P/P0 = 0.2 suggest that
0.005
synthesis steaming caused developing of a significant amorphous phase and the redistribution of the crystalline phase to smaller pore sizes [27,28]. The amounts of nitrogen adsorbed by the mesoporous TS-1 depended on the amount of carbon that was added into the synthesis mixture. The pore size distribution of mesoporous TS-1 was shown in Fig. 5. All the samples possess mesopores with sizes in the range of 10–20 nm widths. This diameter matches with the Carbon Black pearl 2000 particles having an average particle size of 12 nm occupied these positions before combustion
22 20
0.003
(d)
Cyclohexene
18
0.002 (a) (b) (c)
0.001
16
Conversion / %
Pore Volume (cm3/g)
0.004
(d)
14
5
10
15
20
25
30
35
40
45
50
55
(e)
10 8
(e)
0.000
(c) (b)
12
6
60
(a)
4
Pore Diameter (nm)
2
Fig. 5. Pore size distribution of C (a) 10 wt%, (b) 20 wt%, (c) 30 wt%, and (d) 40 wt% of mesoporous TS-1 prepared by microwave synthesis and (e) microporous TS-1.
50
100
150
200
250
300
Reaction time (min) 10
Cyclooctene
C 10 wt% TS-1 MW C 20 wt% TS-1 MW C 30 wt% TS-1 MW C 40 wt% TS-1 MW Microporous TS-1
SBET (m2/g)b
SMicro (m2/g)b
SMeso (m2/g)b
VMicro (cm3/g)c
VMeso (cm3/g)c
422 416 360 382 348
283 172 122 110 203
139 242 239 272 145
0.12 0.09 0.06 0.06 0.14
0.10 0.13 0.13 0.14 0.08
8
Conversion / %
Catalyst
a
(d)
9
Table 1 Properties of C 10, 20, 30, and 40 wt% of mesoporous TS-1 prepared by microwave synthesis and microporous TS-1.
7
(c) (b)
6
(a)
5 (e) 4 3
a
The numbers 10–40 and C represents the weight ratio of C to Si, and Carbon Black pearl 2000, respectively. And microporous TS-1 represents conventional TS-1 without adding C. b Calculated by BET method. c Calculated by BJH method (desorption).
2 1 50
100
150
200
250
300
Reaction time (min) 6.0
6
Cyclododecene
(d)
5.5 5.0
4
Conversion / %
Intensity(a. u.)
5
(b)
3
2
(a)
4.5
(c)
4.0 3.5 3.0
(b)
2.5 2.0
(a) (e)
1.5 1.0
1
0 900
0.5 50 1000
1100
1200
-1
Raman shift (cm ) Fig. 6. Raman spectra of (a) C 20 wt% and (b) 40 wt% of mesoporous TS-1.
100
150
200
250
300
Reaction time (min) Fig. 7. Epoxidation of cyclohexene, cyclooctene, and cyclododecene over C (a) 10 wt%, (b) 20 wt%, (c) 30 wt%, and (d) 40 wt% mesoporous TS-1 prepared by microwave synthesis and (e) microporous TS-1.
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D.-Y. Ok et al. / Microporous and Mesoporous Materials 141 (2011) 2–7
Table 2 Epoxidation of (a) cyclohexene, (b) cyclooctene, and (c) cyclododecene over C 10, 20, 30, and 40 wt% mesoporous TS-1 prepared by microwave synthesis and microporous TS-1. Catalyst
Conversion (%)
(a) Epoxidation of cyclohexene C 10 wt% TS-1 MW 5.1 C 20 wt% TS-1 MW 12 C 30 wt% TS-1 MW 12.3 C 40 wt% TS-1 MW 21.1 Microporous TS-1 11.1 (b) Epoxidation of cyclooctene Catalyst
C 10 wt% TS-1 MW C 20 wt% TS-1 MW C 30 wt% TS-1 MW C 40 wt% TS-1 MW Microporous TS-1
Product distribution (%)
Yield of epoxide (%)
Epoxide
1,2-Cyclohexandiol
2-Cyclohexene-1-one
2-Cyclohexen-1-ol
Others
29 21 20 24 29
11 16 18.6 15.7 10.8
38 31.5 32.9 38.4 39
5.7 14.6 21.1 9.5 4.9
16.3 16.9 7.4 12.4 16.3
Conversion (%)
Product distribution (%)
1.5 1.5 2.5 5.1 3.2
Yield of epoxide (%)
Epoxide
2-Cyclooctene-1-one
Others
5.9 6.8 7.4 9.3 4.5
46.5 80.1 83.5 82 50
17.8 6.5 6.5 5.8 15.9
35.7 13.4 10 12.2 34.1
2.7 5.4 6.2 7.6 2.3
1.5 2.7 4.2 5.7 1.3
69 54 47 41 55
21.5 32 39 46.3 34.9
1.0 1.5 2.0 2.3 0.7
(c) Epoxidation of cyclododecene 2-Cyclododecene-1-one C 10wt% TS-1 MW C 20wt% TS-1 MW C 30wt% TS-1 MW C 40wt% TS-1 MW Microporous TS-1
9.5 14 14 12.7 10.1
Reaction condition: 50 mg catalyst was activated @ 100 °C for 2 h, temperature 70 °C, reaction time 5 h, cycloolefins:H2O2 (30 wt%) = 20:10 mmol, methanol 20 ml as a solvent.
at 550 °C. Broader peak around 30 nm was developed at C 40 wt% mesoporous TS-1 than other C 10, 20, and 30 wt% templated mesoporous TS-1. The physical properties of the mesoporous TS-1 synthesized with different carbon content are displayed in Table 1. BET surface area of all samples has similar value of high surface range from 300 to 400 m2/g that were developed by carbon templating method. The mesopore surface area of carbon templated mesoporous TS-1 prepared by microwave synthesis increased from 139 to 272 m2/g, in parallel micropore pore volume decreased from 0.12 to 0.06 cm3/g (Table 1). It apparently indicated that the mesopore of the carbon templated mesoporous TS-1 materials prepared by microwave synthesis were well-developed in TS-1 zeolite crystal with the amount of carbon. And the pore volume of carbon template mesoporous TS-1 is getting bigger with the increase of carbon adding due to the aggregation of carbon particle each other. The transition metal ions and the coordination state of Ti species substituted in the framework of the mesoporous TS-1 catalyst were identified by UV-Raman spectroscopy. Since most transition metal ions doped in zeolites or mesoporous zeotypes give a charge-transfer transition in the UV or near UV region, the resonance Raman effect can selectively enhance Raman bands that are associated with framework transition metals in framework sites while keeping the other Raman bands unchanged. Thus, it helps to identify the related species [29,30]. UV-Raman spectra of 20 and 40 wt% carbon templated mesoporous TS-1 are shown as Fig. 6. For these samples, Raman band at 970, 1110, and 1150 cm 1. While the band at 970 cm 1 assigned to the surface silanol groups. The UV-Raman spectra clearly shows band at 1110 cm 1 may be assigned as framework titanium species with tetrahedral coordination (Ti–O–Ti). The catalytic activity of these materials was tested for the epoxidation of cyclic-olefins to produce the epoxide at 70 °C using aqueous hydrogen peroxide as an oxidant. TS-1 has redox property that was contributed by tetrahedrally incorporated titanium species in the zeolite framework [31]. The catalytic epoxidation reaction of cyclohexene, cyclooctene, and cyclododecene was shown in
the Fig. 7 and Table 2. The selectivity towards the corresponding epoxides was also described in Table 2. The catalytic activities of five samples are evaluated by plotting the conversion as a function of time. Interestingly, in the case of cyclohexene epoxidation reaction could not observe any specific difference of the catalytic activity between carbon templated mesoporous TS-1 synthesized by microwave method and conventional TS-1 synthesized by hydrothermal method, the reason may be due to the small size of reactant that could not be limited by intra-crystalline diffusion and hence not dependent on whether microporous zeolite crystal or mesopore. So it showed similar catalytic activities with other carbon template mesoporous TS-1. In comparison, both cyclooctene and cyclododecene, every carbon templated mesoporous TS-1 synthesized by microwave has more superior catalytic activities than microporous TS-1 synthesized by hydrothermal method. TS-1 synthesized by hydrothermal method shows lower activity than carbon template mesoporous TS-1, which is attributed to its smaller pore size, making it difficult for large size cycloolefins to interact with the active Ti atoms present within the pores. So those results indicate that carbon particles can enhance the catalytic activity of TS-1 by widening the active sites to interact with bulkier molecules.
3. Conclusion Carbon template mesoporous TS-1 having single-crystal shape was successfully prepared by using microwave synthesis. The amounts of larger mesopores were proportional to the amounts of carbon used as a hard template. Although carbon was added, excellent crystalline product was observed because of carbon play a major role as a microwave absorber to give better crystallinity of the product. Carbon template mesoporous TS-1 (MW) catalyst showed higher catalytic activity than typical microporous TS-1 prepared in hydrothermal conditions. Mesoporous TS-1 prepared by microwave synthesis with varying the amounts of carbon resulted the increase of catalytic activities compared to the amounts of
D.-Y. Ok et al. / Microporous and Mesoporous Materials 141 (2011) 2–7
larger mesoporosities. Epoxidation of cyclooctene and cyclododecene over carbon template mesoporous TS-1 showed the good shape-selectivities contrary to the epoxidation of cyclohexene. Acknowledgment This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MEST) (No. 2009-0083073). References [1] M. Taramasso, G. Perego, B. Notri, U.S. Patent 4 (1983) 501. [2] T. Tastumi, M. Nakanura, S. Negishi, H. Tominnaga, J. Chem. Soc., Chem. Commun. (1990) 476. [3] J.-W. Yoo, C.-W. Lee, J.-S. Chang, S.-E. Park, J. Ko, Catal. Lett. 66 (2000) 169. [4] B. Notari, Stud. Surf. Sci. Catal. 37 (1988) 413. [5] A. Thangaraj, S. Sivasanker, P. Ratnasamy, J. Catal. 137 (1992) 252. [6] G. Caeiro, R.H. Carvalho, X. Wang, M.A.N.D.A. Lemos, R. Lemos, M. Guisnet, F. Ramôa Ribeiro, J. Mol. Catal. A: Chem. 255 (2006) 131. [7] M.-O. Coppens, in: A. Cybulski, J.A. Moulijn (Eds.), Structured Catalysts and Reactors, second ed., CRC Press, New York, 2006. [8] E. Johannessen, G. Wang, M.-O. Coppens, Ind. Eng. Chem. Res. 46 (2007) 4245. [9] G.A. Eimer, I. Diaz, E. Sastre, S.G. Casuscelli, M.E. Crivello, E.R. Herrero, J. PerezPariente, Appl. Catal. A: General 343 (2008) 77. [10] I. Schmidt, A. Krogh, K. Wienberg, A. Carlsson, M. Brorson, C.J.H. Jacobsen, Chem. Commun. (2000) 2157.
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