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Effect of sol–gel synthesis parameters and Cu loading on the physicochemical properties of a new SUZ-4 zeolite
Colloids and Surfaces A: Physicochem. Eng. Aspects 377 (2011) 187–194
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Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Effect of sol–gel synthesis parameters and Cu loading on the physicochemical properties of a new SUZ-4 zeolite Patcharin Worathanakul a,∗ , Dusadee Trisuwan a , Amarin Phatruk b , Paisan Kongkachuichay b,c,d a
Department of Chemical Engineering, King Mongkut’s University of Technology North Bangkok 1518 Pibulsongkram Road, Wongsawang, Bangsue, Bangkok 10800, Thailand Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand National Center of Excellence for Petroleum, Petrochemicals and Advanced Materials, Kasetsart University, Bangkok 10900, Thailand d Center for Advanced Studies in Nanotechnology for Chemical, Food and Agricultural Industries, Kasetsart University, Bangkok, 10900 Thailand b c
a r t i c l e
i n f o
Article history: Received 4 August 2010 Received in revised form 16 December 2010 Accepted 22 December 2010 Available online 13 January 2011 Keywords: SUZ-4 zeolite Copper loading Bagasse ash Silica sol Sol–gel synthesis
a b s t r a c t SUZ-4 zeolites were synthesized hydrothermally using bagasse ash (BA) as a co-silica source and tetraethlyammonium hydroxide as a template, with synthesis occurring at a SiO2 :Al2 O3 ratio of 21.2 under autogenous pressure. Different amounts of copper (II) were loaded in the K+ /SUZ-4 with different weight percentages: 2.3, 2.8, 3.3 and 5.5. The physico-chemical characterization of the obtained SUZ-4 and Cu-loaded SUZ-4 were investigated using X-ray powder diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), X-ray fluorescence (XRF), BET-N2 adsorption, and Fourier transform infrared spectroscopy (FTIR). The results show that Cu loading did not change the structure of SUZ-4. The obtained SUZ-4 zeolite has a narrow pore size distribution and a needle-shaped crystal with approximately 0.07 m mean diameter. The increase in BA content did, however, change the total pore volume and BET surface area, due to the competitive formation of merlinoite zeolite (MER), phillipsite (PHI) and Linde Type F during the crystallization process. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Over the past few decades, a large number of zeolite structures have been synthesized. There are approximately 175 unique zeolite frameworks identified by the International Zeolites Association (IZA) [1], and over 40 naturally occurring zeolite frameworks are known. SUZ-4 is a new type of synthetic zeolite [2–6]. Its topology consists of a three-dimensional pore system having straight tenmembered channels intersected by two eight-membered channels [7]. Many researchers have focused on synthesis, characterization, and catalysis of zeolites. The large and medium pore zeolites after having been ion exchanged with selected metal cations exhibit high activity for reducing NOx . Cu-exchanged zeolites have been widely investigated and found to have potential use as catalysts for NOx reduction [8–11]. The best results have mostly been associated with the ZSM-5 zeolite structure. However, a major drawback to the structure is the de-alumination that occurs under working conditions and causes catalytic deactivation [11]. Fortunately, it has been demonstrated and claimed that SUZ-4 possesses excellent catalytic properties and high thermal stability, as well as high resistance to organic solvents [7,11–17]. Hence, it is of interest to synthesize
∗ Corresponding author. Tel.: +66 29132500x8242; fax: +66 25870024. E-mail addresses: [email protected], patcharin [email protected] (P. Worathanakul). 0927-7757/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2010.12.034
SUZ-4 from low-cost materials or solid wastes and to investigate the physico-chemical properties of Cu/SUZ-4 zeolites before using them as catalysts in NOx reduction. Biomass is a renewable resource, which, due to environmental considerations and the increasing demands of energy worldwide, is used extensively. Bagasse ash (BA) with high silica content is one of the alternative sources for production of valuable materials and chemicals. Crystalline silica in BA is formed at high temperatures and is recognized as a material that can cause respiratory tract disease and, according to the International Agency for Research on Cancer (IARC), cancer. To protect the environment and to decrease the amount of BA waste (and its required storage area), appropriate usage strategies must be found. Several studies have investigated bagasse ash for potential applications and have synthesized various types of zeolites and other materials, such as silica gel as an adsorbent, raw materials for ceramics, cements and concrete additives, catalysts, cosmetics, paint and coating [18–20]. However, the preparation of a SUZ-4 from BA has not been reported yet. Therefore, it is of interest to synthesize and characterize this type of zeolite to find out the optimum conditions for synthesis and using this zeolite as a catalyst for NOx reduction. In this work, different molar ratios of SiO2 and Al2 O3 , crystallization time and temperature were studied to determine the optimal condition of gel parameters. Copper loading in the SUZ-4 zeolite and its thermal stability were also investigated. BA was then used as a silica source instead of silica sol, since it is abundantly sup-
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plied in the sugar industries of Thailand. Different molar ratios of BA and silica sol were prepared in order to obtain the desired SUZ4 zeolite. The pristine SUZ-4 zeolite and Cu-loaded SUZ-4 were analyzed using X-ray powder diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), X-ray fluorescence (XRF), BET-N2 adsorption and Fourier transform infrared spectroscopy (FTIR). With the physico-chemical properties discussed here, Cu-loaded SUZ-4 has a potential to be used as a catalyst for NOx reduction (analysis of which is reserved for future work). 2. Materials and methods 2.1. Materials and BA preparation The materials used to synthesize SUZ-4 zeolite are as follows. Aluminum powder (99.7% Al, Hi Media), silica sol (LUDOX AS40 colloidal silica, 40 wt.% SiO2 , Aldrich), tetraethylammonium hydroxide (TEAOH, 35% in water, Aldrich), potassium hydroxide (85% KOH pellet, Carlo Erba), hydrochloric acid (37 wt.% HCl, Merck), and sodium hydroxide (99% NaOH pellet, Merck) were used as a source of alumina, silica, template, alkali, and acidic and basic leaching, respectively. Bagasse ash (BA), the main raw material used as a silica source, was obtained from sugar factory boilers. It was well washed and boiled with 2 M NaOH for 1 h. The solution was filtered and sodium silicate was then obtained as filtrate. To produce silica gels, the solution was titrated with 1 M HCl until neutral condition was achieved. The soft gel was further aged for 18 h and it was added 100 ml of de-ionized water. It was then filtered, washed with distilled water, and dried at 80 ◦ C for 12 h. The obtained white ash (BA) was further used as a natural silica source.
stainless steel reactor (Parr Model 4561, USA) for crystallization under autogenous pressure. The BA and silica sol were used as silica sources with BA: silica sol molar ratio of 0:100, 25:75, 50:50 and 100:0. Preparing a SUZ-4 zeolite with the starting composition of 7.9K2 O:Al2 O3 :21.2SiO2 :2.6TEA2 O:499H2 O, following steps were carried out. Firstly, a solution containing potassium aluminate solution was prepared by dissolving 4.92 g of KOH and 0.49 g of aluminum powder. Next, a solution containing BA:silica sol was prepared by adjusting the molar ratio of BA and silica sol in the range of 0–100%. TEAOH was added into the silica solution. Subsequently, both solutions were mixed inside a teflon cup and vigorously stirred for 3 h. The resulting white gel was formed and then transferred to the autoclave, in which the gel was stirred for crystallization at 150 ◦ C under autogenous pressure for 4 days. The powder product was filtered, washed thoroughly with distilled water, dried at 120 ◦ C for 2 h, and finally calcined at 550 ◦ C for 4 h. 2.3. Ion-exchange of K+ /SUZ-4 and thermal stability Copper (II) exchanged SUZ-4 zeolite was prepared with different percentages of Cu loading (Table 1) by an aqueous ion exchange method, with vigorous stirring using a dilute solution of copper acetate (99.5 wt.%, AR Grade, QRëCTM ) in solid–liquid ratio of 1 g/100 ml at room temperature for 24 h. The ion-exchanged zeolite was then filtered and washed thoroughly with de-ionized water before drying at 120 ◦ C for 12 h. The samples were then calcined at 500 ◦ C for 6 h. The thermal stabilities of the samples were tested by treating the samples in air at various temperatures in the range of 400–700 ◦ C. 2.4. Material characterization
2.2. SUZ-4 synthesis The effects of corresponding factors (i.e., gel composition (SiO2 /Al2 O3 ), crystallization temperature and time) listed in Table 1 were studied to obtain SUZ-4 zeolite. The precursor gels of aluminosilicate were prepared following methods reported in our previous study and others [6,21,22], using the following molar ratios: (3.96–7.9)K2 O:Al2 O3 :(16.2–33.5)SiO2 : (0.92–3.10)TEA2 O:(450–812)H2 O. Firstly, KOH was dissolved in distilled water; aluminum powder was then added to this solution in a loosely capped bottle (H2 gas was evolved during this step); the mixture was stirred continuously until the aluminum was completely dissolved, forming a clear solution. Secondly, an aqueous solution of LUDOX and TEAOH was prepared and then it was poured into the aluminum solution under vigorous stirring. Subsequently, a white gel was formed and mixed thoroughly until an even consistency was achieved. Next, it was transferred to an autoclave Table 1 List of experiments performed. K+ /SUZ-4 SiO2 precursor Al2 O3 precursor Structure directing agent SiO2 :Al2 O3 molar ratio Temperature and crystallization time BA: silica sol molar ratio Cu2+ /SUZ-4 Metal loading wt.% Cu loading Thermal stability of SUZ-4
Silica sol and bagasse ash (BA) Aluminum powder Tetraethylammonium hydroxide (TEAOH) 16.2, 21.2, 33.3 150 ◦ C for 4 days, 165 ◦ C for 2 days 0:100, 25:75, 50:50 and 100:0 (at SiO2 :Al2 O3 = 21.2, 155 ◦ C for 4 days) Copper(II) acetate 2.3,2.8, 3.3, 5.5 (at BA:silica sol = 0:100) 400, 500, 600, 700 ◦ C (at 2.3 wt.% Cu loading)
2.4.1. X-ray powder diffraction (XRD) The crystal structure of synthesized SUZ-4 zeolites was determined by using X-ray powder diffraction (Phillips PW 1830/40) ˚ generator tension 40 kV and with Cu-K˛ 1 radiation ( = 1.5406 A), generator current 30 mV, and scanning in the range of 5–70◦ (2) with a rate of 0.01◦ /min. 2.4.2. X-ray fluorescence spectroscopy (XRF) Chemical analysis was determined by using X-ray fluorescence (XRF HORIBA, MESA 500-WX-ray fluorescence spectrometry) with a 15/50 keV X-ray tube. Quantitative analysis of the silica content was performed without any preparatory work, such as calibration using standard samples or the pre-registration of a standard spectrum. 2.4.3. Scanning electron microscopy (SEM) The crystal morphology and size of the obtained zeolite were determined via scanning electron microscopy (SEM) with energy dispersive spectroscopy (Jeol, JSM-6301F and Phillips, XL30). The sample was coated with a thin layer of gold using a sputter coater (Edwards Laboratories, Milpitas, CA). 2.4.4. BET N2 -adsorption/desorption isotherm Specific surface area (SSA), adsorption/desorption isotherms, pore size and pore size distribution (PSD) of the prepared samples were determined using BET-N2 adsorption (Quantachrome, Autosorb® -1-C) with micropore analysis (74 points N2 adsorption/desorption). 2.4.5. Fourier transform infrared spectroscopy (FTIR) The surface chemical bonding was observed by a Fourier transform infrared spectroscopy (FTIR, Perkin Elmer, Spectrum One, USA). The diffuse reflectance infrared Fourier transform (DRIFT) technique was used for all samples to identify types of
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patterns with different SiO2 /Al2 O3 ratios for 4 days crystallization. Using a SiO2 /Al2 O3 ratio of 32.4, the pattern reveals the co-existence of mordenite (MOR) according to known results of competing phase in SUZ-4 synthesis [2,21] whereas a ratio of SiO2 /Al2 O3 = 16.3 shows a merlinotie (MER) and alpha quartz phase co-existing with SUZ-4. However, with SiO2 /Al2 O3 = 21.2, a high purity SUZ-4 zeolite can be achieved (Fig. 1b). The result shows that the chemical composition of the mixture is very sensitive for SUZ-4 synthesis. It was also observed that gel mixtures with a high SiO2 /Al2 O3 ratio were very viscous and, as the ratio was decreased, the mixtures became less viscous. SEM images of SUZ-4 zeolite obtained after 4 days crystallization are shown in Fig. 2. The images illustrate that most of the crystals are needle-shaped, confirming the formation of SUZ-4 [7,12,22]. However, in Fig. 2c (SiO2 /Al2 O3 = 16.3) some irregularly shaped crystals can be observed. These crystals are the MER and the alpha quartz phase as mentioned earlier. It thus appears that the images found at a higher SiO2 /Al2 O3 ratio gave larger needle-shaped crystals than that obtained at a low ratio (see Table 2). Fig. 1. XRD patterns of SUZ-4 crystals prepared at 155 ◦ C for 4 days with different SiO2 /Al2 O3 ratios: (a) 32.4, (b) 21.2, and (c) 16.3.
chemical bonds (functional groups). The spectral resolution was 4 cm−1 and 256 scans were coded into the mid-infrared region (4000–400 cm−1 ) [23]. 3. Results and discussion 3.1. Using chemical sources for SUZ-4 zeolite synthesis 3.1.1. Effect of SiO2 /Al2 O3 ratios For these experiments, the crystallization reaction time was studied for two conditions: 2 days and 4 days. Fig. 1 shows XRD
3.1.2. Effects of temperature and time of crystallization Two days crystallization time was carried out in the same type of autoclave to confirm the characterization results. However, a higher reaction temperature of 169 ◦ C was controlled in the reactor. Fig. 3 shows XRD patterns with different SiO2 /Al2 O3 ratios for 2-day crystallization. SUZ-4 zeolites were mainly obtained from SiO2 /Al2 O3 ratios of 32.7 and/or 21.2. Using a SiO2 /Al2 O3 ratio of 32.7 still gave some impurities of MOR, and SiO2 /Al2 O3 = 16.2 has been shown to have competing MER, alpha quartz and phillipsite (PHI) phases as product impurities of product according to the results of Gujar and Price [21,22]. A gel mixture of SiO2 /Al2 O3 = 21.2 still gave, under experimental conditions, a good sample of pure synthesized SUZ-4 zeolite. These results are in good agreement with previous reports [6,22]. Moreover, the formation of SUZ-4 zeo-
Fig. 2. SEM micrographs of SUZ-4 crystals prepared at 155 ◦ C for 4 days with different SiO2 /Al2 O3 ratios: (a) 32.4, (b) 21.2, and (c) 16.3.
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Table 2 BET surface area and pore volume of zeolites with different synthesis time and SiO2 /Al2 O3 ratios. Synthesis time (days)
SiO2 /Al2 O3
BET surface area (m2 /g)
Micropore volumea (cm3 /g)
Total pore volumeb (cm3 /g)
Pore diameterc (Å)
Crystallite size d
4
32.4 21.2 16.3
107.0 440.4 145.2
0.0269 0.1089 0.0332
0.1657 1.0360 0.1923
5.4 ± 1.0 5.4 ± 1.0 4.6 ± 0.4
0.09 m dia. × 0.63 m long 0.07 m dia. × 0.64 m long 0.09 m dia. × 1.20 m long
2
33.3 21.2 16.2
76.0 347.6 18.4
0.0071 0.0558 -
0.1441 0.3692 0.1046
5.4 ± 0.6 5.4 ± 1.0 4.6 ± 0.5
0.15 m dia. × 1.09 m long 0.10 m dia. × 0.41 m long 0.12 m dia. × 1.23 m long
a b c d
t-Plot micropore analysis method. MP micropore analysis method at P/P0 close to unity. SF micropore analysis method. Measured from SEM micrographs.
lite is here found to be achieved under the narrow range conditions [22]. The formation of SUZ-4 can be confirmed by the SEM images (Fig. 4) that show needle-shaped crystals of SUZ-4 obtained after 2 days crystallization. The images show that most crystals are needle-shaped. However, the image for SiO2 /Al2 O3 = 16.2 shows some irregular shapes and aggregated crystals, which have been in line with XRD pattern of MER, alpha quartz and phillipsite (PHI) phases shown in Fig. 3. The image clearly shows that, similar to the results of 4 days crystallization, the larger needle-shaped crystals were attained from samples with a higher SiO2 /Al2 O3 ratio. In addition, specific surface areas and pore volumes at different SiO2 /Al2 O3 molar ratios and crystallization times were characterized by BET N2 -adsorption/desorption isotherms, as shown in Table 2. The results clearly demonstrate that a gel mixture composition with a SiO2 /Al2 O3 ratio of 21.2 exhibits a high surface area of 440.45 m2 /g and large total pore volume (1.036 cm3 /g) at P/P0 = 1. Under the conditions employed in the experiments here, synthesis of the most pure SUZ-4 occurred for SiO2 :Al2 O3 ratio of 21.2 after 4 days crystallization at 155 ◦ C under autogenous pressure. This product clearly exhibits a high BET surface area and a total pore volume with a narrow pore size distribution. The overall results obtained here suggest that SUZ-4 synthesis is very sensitive to the gel chemical composition of mixture, the temperature and the crystallization time, since MOR and PHI are common competing phases.
3.1.3. Effect of different copper loadings and thermal stability The composition 7.9K2 O:Al2 O3 :21.2SiO2 :2.6TEA2 O:499H2 O was prepared for determination of the effects of Cu loading and thermal stability of Cu-loaded SUZ-4. As determined by XRF analysis, the chemical compositions of Cu-loaded with different weight percentages are summarized in Table 3 the results show that all Cu2+ /SUZ-4 have Si/Al ratio (by weight) in the range of 7.3–8.3. XRD patterns of the K+ /SUZ-4 and different Cu loading are shown in Fig. 5. There is no detectable change in the background due to degradation of the sample, as well as no detectable formation of CuO in the XRD patterns of Cu2+ /SUZ-4. The detection limit of XRD is normally 3–5 wt.%, but with favorable scattering properties, the minimal amount could be close to 1 wt.%. It is possible that the corresponding peaks of CuO might be below the detection limit of this technique. However, even at a maximum Cu loading of 5.5% that is higher than the detection limit of XRD, no CuO peak was detected. Additionally, the decrease of potassium content shown in Table 3 confirms the success of ion exchange between K+ and Cu2+ . Fig. 6 presents the XRD patterns of Cu2+ /SUZ-4 after being treated at different temperatures. The results reveal that Cu loading and thermal treatment did not alter the SUZ-4 structure. BET surface area and total pore volume of Cu-loaded SUZ-4 are summarized in Table 4. With a high weight percentage of Cu loading, the BET surface area of Cu2+ /SUZ-4 increased, except at 2.8% loading. This is probably due to the use of different scaledup batches for 2.8% Cu loading, which may lead to incomplete ion exchange. Fig. 7 shows the FTIR spectrum in the region of 4000–400 cm−1 for K+ /SUZ-4 and Cu2+ /SUZ-4 at 155 ◦ C crystallization for 4 days with SiO2 /Al2 O3 = 21.2. Frequencies of Si(OH)Al group vibration in zeolites depend generally on local structure and composition. The peaks at 3500 cm−1 and 1682 cm−1 are assigned to isolated silanol groups (Si–OH) and absorption O–H stretching, respectively [16,17]. The peaks at 831 and 1103 cm−1 are assigned to the vibration of Al–O–Si and Si–O stretching, respectively. The vibration of Si–O bending for Si–O–Al and Si–O–Si are located at 573 cm−1 and 470 cm−1 , respectively. There is no IR spectroscopic evidence for the presence of CuO after Cu loading. For all samTable 3 Chemical compositions of Cu-loaded with different weight percentages on SUZ-4 zeolite (wt.% Cu2+ /SUZ-4) using XRF analysis.
Fig. 3. XRD patterns of zeolite SUZ-4 crystals prepared at 168 ◦ C for 2 days with different SiO2 /Al2 O3 : (a) 32.7, (b) 21.2, and (c) 16.2.
Element
K+ /SUZ-4
Cu loading 2.3 wt.%
2.8 wt.%
3.3 wt.%
5.5 wt.%
Si K Al O Cu Fe Others
32.89 17.48 4.48 45.07 0 0.07 0.01
33.00 13.37 4.40 54.73 3.90 0.06 0.02
33.42 12.79 4.04 45.94 3.68 0.07 0.06
32.89 12.17 4.47 45.26 5.11 0.07 0.03
33.03 11.58 4.44 45.36 5.51 0.06 0.02
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Fig. 4. SEM micrographs of zeolite SUZ-4 crystals prepared at 168 ◦ C for 2 days with different SiO2 /Al2 O3 : (a) 33.3, (b) 21.2, and (c) 16.2.
Fig. 5. XRD pattern of different Cu loadings Cu2+ /SUZ-4: (a) K+ /SUZ-4, (b) 2.3 wt.% Cu2+ /SUZ-4, (c) 2.8 wt.% Cu2+ /SUZ-4, (d) 3.3 wt.% Cu2+ /SUZ-4, and (e) 5.5 wt.% Cu2+ /SUZ-4.
Fig. 6. XRD patterns of fresh/treated Cu2+ /SUZ-4 prepared with different thermal treatments: (a) fresh Cu2+ /SUZ-4, (b) 400 ◦ C, (c) 500 ◦ C, (d) 600 ◦ C, and (e) 700 ◦ C.
Table 4 BET surface area with different weight percentages of Cu2+ /SUZ-4. Cu loading (wt.%)
BET surface area (m2 /g)
External surface areaa (m2 /g)
Micropore volumea (cm3 /g)
Total pore volumeb (cm3 /g)
Pore diameterc (Å)
2.3 2.8 3.3 5.5
341.9 300.9 345.2 398.3
232.8 182.3 229.4 267.8
0.0738 0.0861 0.0730 0.0846
0.5199 0.3965 0.6641 0.6885
5.8 5.7 5.7 5.7
a b c
t-Plot micropore analysis method. MP micropore analysis method at P/P0 close to unity. SF micropore analysis method.
± ± ± ±
0.8 0.9 1.0 0.9
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Fig. 8. XRD patterns of prepared BA and synthesized product prepared with different BA: silica sol molar ratios (a) 0:100, (b) 25:75, (c) 50:50, and (d)100:0. Fig. 7. FTIR-spectra of (a) K+ /SUZ-4, (b) 2.3 wt.% Cu2+ /SUZ-4, (c) 2.8 wt.% Cu2+ /SUZ-4, (d) 3.3 wt.% Cu2+ /SUZ-4, and (e) 5.5 wt.% Cu2+ /SUZ-4.
3.2. Bagasse ash as a silica source for SUZ-4 synthesis
ples of Cu loadings, no vibration was observed at 410, 500 and 610 cm−1 , which correspond to the presence of CuO [24–26]. The result shows that no CuO was formed and it might be concluded that only ionic Cu was formed after ion-exchange with the SUZ-4 zeolite. This is in line with XRD pattern that shows no CuO phase in Fig. 5. Nonetheless, one also should keep in mind that the amount of CuO (if formed) might be too small to be detected by the FTIR.
The BA used in this study is composed of 96.1% silica, 2.98% alumina (Al2 O3 ), 0.77% potassium oxide (K2 O), and trace amounts of other metal oxides. The silica in BA is in amorphous form as confirmed by the XRD (Fig. 8). The BA was used as silica source for SUZ-4 zeolite synthesis under autogenous pressure using a stainless steel autoclave at 150 ◦ C; crystallization lasted 4-days. The gel composition of 7.92K2 O:Al2 O3 :21.2SiO2 :2.6TEA2 O:499H2 O was prepared with different BA: silica sol molar ratios (0:100, 25:75, 50:50 and
Fig. 9. SEM micrographs of as-synthesized SUZ-4 with different molar ratios of BA: silica sol (a) 0:100, (b) 25:75, and (c) 50:50.
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Table 5 BET surface area with different BA: silica sol ratios. Silica from BA: silica sol
BET surface area (m2 /g)
External surface areaa (m2 /g)
Micropore volumea (cm3 /g)
Total pore volumeb (cm3 /g)
Pore diameterc (Å)
0:100 25:75 50:50
402.8 351.2 261.7
291.9 200.9 148.8
0.0768 0.1081 0.0812
0.6113 0.4365 0.2859
5.7 ± 0.8 5.8 ± 0.8 5.7 ± 0.9
a b c
t-Plot micropore analysis method. MP micropore analysis method at P/P0 close to unity. SF micropore analysis method.
100:0). XRD patterns of the synthesized products with different BA amounts are presented in Fig. 8. The corresponding phases were identified by comparison with the reported standard patterns [7,22,27]. It is evident that when BA was added into the silica sol, the height of the corresponding peaks of SUZ-4 decreased and MER, PHI, and Linde Type F [28,29] were formed when the only silica source used was BA (100:0). The Si/Al ratios of the impurities formed (i.e., 1.9, 2.6 and 1.0, for MER, PHI and Linde Type F, respectively) are much lower than that of SUZ-4 (Si/Al = 6.2) [21]; this implies that formation of the competing phases requires less silica than SUZ-4. It should be highlighted that, in this study, BA was used as amorphous solid, while the silica sol was in the form of colloidal solution. Thus, the BA required a longer time to be dissolved completely to form silicate units, compared to the time required silica sol (which has a higher activity). Moreover, zeolite crystallization is a competitive reaction depending on the controlled conditions and on the nature of each chemical species involved. Therefore, when BA alone was used as a source of silica, the availability of silicate units was quite limited and favored the formation of MER, PHI and Linde Type F instead of the SUZ-4 zeolite. It is worth mentioning that the impurities of other compounds in prepared BA may affect on the formation of the SUZ-4. These results are in good agreement with those of Gujar et al. [7], who reported that SUZ-4 formation occurred in a narrow range of conditions and was very sensitive to various factors. SEM micrographs of the products were taken as shown in Fig. 9. The pictures confirm the formation of SUZ-4 as needle-shaped crystals. It is also found that the crystal of SUZ-4 was approximately 0.07 m in diameter and 0.61 m long; these results are close to those for SUZ-4 synthesized from a chemical source at a SiO2 /Al2 O3 ratio of 21.2 after 4-days, as shown in Table 2 (0.07 m dia. × 0.64 m long). ˚ this The mean size of obtained SUZ-4 is approximately 5.7 A; is the size of the open channel inside the SUZ-4 structure [3]. The surface area, the micropore volume, and the total pore volume of the products were also analyzed and are summarized in Table 5. The results clearly show that the surface area and pore volume are directly related to the amount of SUZ-4 formed. With increasing BA contents, the surface area and pore volume decrease as the result of the formation of impurities. 4. Conclusions SUZ-4 zeolites have been successfully synthesized under different conditions. With TEAOH as a structure directing agent, a good sample of synthesized SUZ-4 zeolite can be produced from a gel mixture of SiO2 /Al2 O3 = 21.2 under autogenous pressure using a stainless steel autoclave at 150 ◦ C for 4 days. Different BA:silica sol ratios did change the purity of the obtained SUZ-4. The differences in crystal size, specific surface areas, pore volume and pore size distribution have been reported. Copper (II) loading did not change the SUZ-4 zeolite structure, and no CuO formation was found. Increasing the content of BA to 50%, a high purity of SUZ-4 was still obtained with 262 m2 /g surface area is. Using more BA together with silica
sol, mono-distribution of pores having a mean size of approximately 5.7 A˚ was obtained. When 100% BA was added, competing phases (MER, PHI and Linde Type F) were formed, and no SUZ-4 zeolite was found. From this study, we conclude that bagasse ash can be used as co-silica-source for SUZ-4 synthesis, thus allowing the use of some bagasse waste. More studies however are required to fully access its range of applications and its economical limitations. Acknowledgements The authors gratefully acknowledge the financial support of Thailand Research Fund (TRF) under grant number MRG5280110 and TRF-master research grants and Khonburi Sugar Company Limited under grant number MRG-WI525E092. We also acknowledge the grant for research publications (Amarin Phatruk) from the Graduate School Kasetsart University and research grants from the Kasetsart University Research and Development Institute (KURDI) and the Commission on Higher Education, Ministry of Education, the “National Research University Project of Thailand (NRU)”. References [1] International Zeolite Association, Database of Zeolite Structures, http://www. iza-structure.org/databases (accessed 10.05.2010). [2] S.A. Barri, Crystalline (Metallo) Silicates and Germanates-SUZ-4, United States, 5,118,483, 1992. [3] S.L. Lawton, J.M. Bennett, J.L. Schlenker, M.K. Rubin, Synthesis and proposed framework topology of zeolite SUZ-4, J. Chem. Soc., Chem. Commun. 11 (1993) 894–896. [4] W.C. Paik, C.H. Shin, J.M. Lee, B.J. Ahn, S.B. Hong, Host–guest interactions in P1, SUZ-4, and ZSM-57 zeolites containing N,N,N,N ,N N hexaethylpentanediammonium ion as a guest molecule, J. Phys. Chem. B 105 (2001) 9994–10000. [5] K.G. Strohmaier, M. Afeworki, D.L. Dorset, The crystal structures of polymorphic SUZ-4, Z. Kristallogr. 221 (2006) 689–698. [6] P. Worathanakul, P. Kongkachuichay, New SUZ-4 zeolite membrane from sol–gel technique, Int. J. Chem. Biomol. Eng. 1 (2008) 131–135. [7] A.C. Gujar, A.A. Moye, P.A. Coghill, D.C. Teeters, K.P. Roberts, G.L. Price, Raman investigation of the SUZ-4 zeolite, Micropor. Mesopor. Mater. 78 (2005) 131–137. [8] S. Bhattacharyya, R.K. Das, Catalytic reduction of NOx in gasoline engine exhaust over copper-and nickel-exchanged X-zeolite catalysts, Energy Convers. Manage. 42 (2001) 2019–2027. [9] A.E. Palomares, F. Marquez, S. Valencia, A. Corma, On the researching of a new zeolite structure for the selective catalytic reduction of NO: the possibilities of Cu-exchanged IM5, J. Mol. Catal. A: Chem. 162 (2000) 175–189. [10] C. Torre-Abreu, C. Henriques, F.R. Ribeiro, G. Delahay, M.F. Ribeiro, Selective catalytic reduction of NO on copper-exchanged zeolites: the role of the structure of the zeolite in the nature of copper-active sites, Catal. Today 54 (1999) 407–418. [11] A. Subbiah, B.K. Cho, R.J. Blint, A.C. Gujar, G.L. Price, J.E. Yie, NOx reduction over metal-ion exchanged novel zeolite under lean conditions: activity and hydrothermal stability, Appl. Catal., B 42 (2003) 155–178. [12] M.A. Asensi, M.A. Camblor, A. Martinez, Zeolite SUZ-4: reproducible synthesis physicochemical characterization and catalytic evaluation for the skeletal isomerization of n-butenes, Micropor. Mesopor. Mater. 28 (1999) 427–436. [13] H. Choo, S.B. Hong, L. Keven, Comparative ESR and catalytic studies of ethylene dimerization on Pd(II)-exchanged clinoptilolite, mordenite, ferrierite, and SUZ4, J. Phys. Chem. B 105 (2001) 7730–7738. [14] S. Jiang, Y.K. Hwang, S.H. Jhung, J.-S. Chang, J.-S. Hwang, Zeolite SUZ-4 as selctive dehydration catalyst for methanol conversion to dimethy ether, Chem. Lett. 33 (2004) 1048–1049. [15] S.-H. Lee, C.-H. Shin, G.J. Choi, T.-J. Park, I.-S. Nam, B. Han, S.B. Hong, Zeolite synthesis in the presence of flexible diquaternary alkylammonium ions (C2 H5 )3 N+ (CH2 )N+ (C2 H5 )3 with n = 3–10 as structure-directing agents, Micropor. Mesopor. Mater. 60 (2003) 237–249.
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Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Effect of sol–gel synthesis parameters and Cu loading on the physicochemical properties of a new SUZ-4 zeolite Patcharin Worathanakul a,∗ , Dusadee Trisuwan a , Amarin Phatruk b , Paisan Kongkachuichay b,c,d a
Department of Chemical Engineering, King Mongkut’s University of Technology North Bangkok 1518 Pibulsongkram Road, Wongsawang, Bangsue, Bangkok 10800, Thailand Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand National Center of Excellence for Petroleum, Petrochemicals and Advanced Materials, Kasetsart University, Bangkok 10900, Thailand d Center for Advanced Studies in Nanotechnology for Chemical, Food and Agricultural Industries, Kasetsart University, Bangkok, 10900 Thailand b c
a r t i c l e
i n f o
Article history: Received 4 August 2010 Received in revised form 16 December 2010 Accepted 22 December 2010 Available online 13 January 2011 Keywords: SUZ-4 zeolite Copper loading Bagasse ash Silica sol Sol–gel synthesis
a b s t r a c t SUZ-4 zeolites were synthesized hydrothermally using bagasse ash (BA) as a co-silica source and tetraethlyammonium hydroxide as a template, with synthesis occurring at a SiO2 :Al2 O3 ratio of 21.2 under autogenous pressure. Different amounts of copper (II) were loaded in the K+ /SUZ-4 with different weight percentages: 2.3, 2.8, 3.3 and 5.5. The physico-chemical characterization of the obtained SUZ-4 and Cu-loaded SUZ-4 were investigated using X-ray powder diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), X-ray fluorescence (XRF), BET-N2 adsorption, and Fourier transform infrared spectroscopy (FTIR). The results show that Cu loading did not change the structure of SUZ-4. The obtained SUZ-4 zeolite has a narrow pore size distribution and a needle-shaped crystal with approximately 0.07 m mean diameter. The increase in BA content did, however, change the total pore volume and BET surface area, due to the competitive formation of merlinoite zeolite (MER), phillipsite (PHI) and Linde Type F during the crystallization process. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Over the past few decades, a large number of zeolite structures have been synthesized. There are approximately 175 unique zeolite frameworks identified by the International Zeolites Association (IZA) [1], and over 40 naturally occurring zeolite frameworks are known. SUZ-4 is a new type of synthetic zeolite [2–6]. Its topology consists of a three-dimensional pore system having straight tenmembered channels intersected by two eight-membered channels [7]. Many researchers have focused on synthesis, characterization, and catalysis of zeolites. The large and medium pore zeolites after having been ion exchanged with selected metal cations exhibit high activity for reducing NOx . Cu-exchanged zeolites have been widely investigated and found to have potential use as catalysts for NOx reduction [8–11]. The best results have mostly been associated with the ZSM-5 zeolite structure. However, a major drawback to the structure is the de-alumination that occurs under working conditions and causes catalytic deactivation [11]. Fortunately, it has been demonstrated and claimed that SUZ-4 possesses excellent catalytic properties and high thermal stability, as well as high resistance to organic solvents [7,11–17]. Hence, it is of interest to synthesize
∗ Corresponding author. Tel.: +66 29132500x8242; fax: +66 25870024. E-mail addresses: [email protected], patcharin [email protected] (P. Worathanakul). 0927-7757/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2010.12.034
SUZ-4 from low-cost materials or solid wastes and to investigate the physico-chemical properties of Cu/SUZ-4 zeolites before using them as catalysts in NOx reduction. Biomass is a renewable resource, which, due to environmental considerations and the increasing demands of energy worldwide, is used extensively. Bagasse ash (BA) with high silica content is one of the alternative sources for production of valuable materials and chemicals. Crystalline silica in BA is formed at high temperatures and is recognized as a material that can cause respiratory tract disease and, according to the International Agency for Research on Cancer (IARC), cancer. To protect the environment and to decrease the amount of BA waste (and its required storage area), appropriate usage strategies must be found. Several studies have investigated bagasse ash for potential applications and have synthesized various types of zeolites and other materials, such as silica gel as an adsorbent, raw materials for ceramics, cements and concrete additives, catalysts, cosmetics, paint and coating [18–20]. However, the preparation of a SUZ-4 from BA has not been reported yet. Therefore, it is of interest to synthesize and characterize this type of zeolite to find out the optimum conditions for synthesis and using this zeolite as a catalyst for NOx reduction. In this work, different molar ratios of SiO2 and Al2 O3 , crystallization time and temperature were studied to determine the optimal condition of gel parameters. Copper loading in the SUZ-4 zeolite and its thermal stability were also investigated. BA was then used as a silica source instead of silica sol, since it is abundantly sup-
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plied in the sugar industries of Thailand. Different molar ratios of BA and silica sol were prepared in order to obtain the desired SUZ4 zeolite. The pristine SUZ-4 zeolite and Cu-loaded SUZ-4 were analyzed using X-ray powder diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), X-ray fluorescence (XRF), BET-N2 adsorption and Fourier transform infrared spectroscopy (FTIR). With the physico-chemical properties discussed here, Cu-loaded SUZ-4 has a potential to be used as a catalyst for NOx reduction (analysis of which is reserved for future work). 2. Materials and methods 2.1. Materials and BA preparation The materials used to synthesize SUZ-4 zeolite are as follows. Aluminum powder (99.7% Al, Hi Media), silica sol (LUDOX AS40 colloidal silica, 40 wt.% SiO2 , Aldrich), tetraethylammonium hydroxide (TEAOH, 35% in water, Aldrich), potassium hydroxide (85% KOH pellet, Carlo Erba), hydrochloric acid (37 wt.% HCl, Merck), and sodium hydroxide (99% NaOH pellet, Merck) were used as a source of alumina, silica, template, alkali, and acidic and basic leaching, respectively. Bagasse ash (BA), the main raw material used as a silica source, was obtained from sugar factory boilers. It was well washed and boiled with 2 M NaOH for 1 h. The solution was filtered and sodium silicate was then obtained as filtrate. To produce silica gels, the solution was titrated with 1 M HCl until neutral condition was achieved. The soft gel was further aged for 18 h and it was added 100 ml of de-ionized water. It was then filtered, washed with distilled water, and dried at 80 ◦ C for 12 h. The obtained white ash (BA) was further used as a natural silica source.
stainless steel reactor (Parr Model 4561, USA) for crystallization under autogenous pressure. The BA and silica sol were used as silica sources with BA: silica sol molar ratio of 0:100, 25:75, 50:50 and 100:0. Preparing a SUZ-4 zeolite with the starting composition of 7.9K2 O:Al2 O3 :21.2SiO2 :2.6TEA2 O:499H2 O, following steps were carried out. Firstly, a solution containing potassium aluminate solution was prepared by dissolving 4.92 g of KOH and 0.49 g of aluminum powder. Next, a solution containing BA:silica sol was prepared by adjusting the molar ratio of BA and silica sol in the range of 0–100%. TEAOH was added into the silica solution. Subsequently, both solutions were mixed inside a teflon cup and vigorously stirred for 3 h. The resulting white gel was formed and then transferred to the autoclave, in which the gel was stirred for crystallization at 150 ◦ C under autogenous pressure for 4 days. The powder product was filtered, washed thoroughly with distilled water, dried at 120 ◦ C for 2 h, and finally calcined at 550 ◦ C for 4 h. 2.3. Ion-exchange of K+ /SUZ-4 and thermal stability Copper (II) exchanged SUZ-4 zeolite was prepared with different percentages of Cu loading (Table 1) by an aqueous ion exchange method, with vigorous stirring using a dilute solution of copper acetate (99.5 wt.%, AR Grade, QRëCTM ) in solid–liquid ratio of 1 g/100 ml at room temperature for 24 h. The ion-exchanged zeolite was then filtered and washed thoroughly with de-ionized water before drying at 120 ◦ C for 12 h. The samples were then calcined at 500 ◦ C for 6 h. The thermal stabilities of the samples were tested by treating the samples in air at various temperatures in the range of 400–700 ◦ C. 2.4. Material characterization
2.2. SUZ-4 synthesis The effects of corresponding factors (i.e., gel composition (SiO2 /Al2 O3 ), crystallization temperature and time) listed in Table 1 were studied to obtain SUZ-4 zeolite. The precursor gels of aluminosilicate were prepared following methods reported in our previous study and others [6,21,22], using the following molar ratios: (3.96–7.9)K2 O:Al2 O3 :(16.2–33.5)SiO2 : (0.92–3.10)TEA2 O:(450–812)H2 O. Firstly, KOH was dissolved in distilled water; aluminum powder was then added to this solution in a loosely capped bottle (H2 gas was evolved during this step); the mixture was stirred continuously until the aluminum was completely dissolved, forming a clear solution. Secondly, an aqueous solution of LUDOX and TEAOH was prepared and then it was poured into the aluminum solution under vigorous stirring. Subsequently, a white gel was formed and mixed thoroughly until an even consistency was achieved. Next, it was transferred to an autoclave Table 1 List of experiments performed. K+ /SUZ-4 SiO2 precursor Al2 O3 precursor Structure directing agent SiO2 :Al2 O3 molar ratio Temperature and crystallization time BA: silica sol molar ratio Cu2+ /SUZ-4 Metal loading wt.% Cu loading Thermal stability of SUZ-4
Silica sol and bagasse ash (BA) Aluminum powder Tetraethylammonium hydroxide (TEAOH) 16.2, 21.2, 33.3 150 ◦ C for 4 days, 165 ◦ C for 2 days 0:100, 25:75, 50:50 and 100:0 (at SiO2 :Al2 O3 = 21.2, 155 ◦ C for 4 days) Copper(II) acetate 2.3,2.8, 3.3, 5.5 (at BA:silica sol = 0:100) 400, 500, 600, 700 ◦ C (at 2.3 wt.% Cu loading)
2.4.1. X-ray powder diffraction (XRD) The crystal structure of synthesized SUZ-4 zeolites was determined by using X-ray powder diffraction (Phillips PW 1830/40) ˚ generator tension 40 kV and with Cu-K˛ 1 radiation ( = 1.5406 A), generator current 30 mV, and scanning in the range of 5–70◦ (2) with a rate of 0.01◦ /min. 2.4.2. X-ray fluorescence spectroscopy (XRF) Chemical analysis was determined by using X-ray fluorescence (XRF HORIBA, MESA 500-WX-ray fluorescence spectrometry) with a 15/50 keV X-ray tube. Quantitative analysis of the silica content was performed without any preparatory work, such as calibration using standard samples or the pre-registration of a standard spectrum. 2.4.3. Scanning electron microscopy (SEM) The crystal morphology and size of the obtained zeolite were determined via scanning electron microscopy (SEM) with energy dispersive spectroscopy (Jeol, JSM-6301F and Phillips, XL30). The sample was coated with a thin layer of gold using a sputter coater (Edwards Laboratories, Milpitas, CA). 2.4.4. BET N2 -adsorption/desorption isotherm Specific surface area (SSA), adsorption/desorption isotherms, pore size and pore size distribution (PSD) of the prepared samples were determined using BET-N2 adsorption (Quantachrome, Autosorb® -1-C) with micropore analysis (74 points N2 adsorption/desorption). 2.4.5. Fourier transform infrared spectroscopy (FTIR) The surface chemical bonding was observed by a Fourier transform infrared spectroscopy (FTIR, Perkin Elmer, Spectrum One, USA). The diffuse reflectance infrared Fourier transform (DRIFT) technique was used for all samples to identify types of
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patterns with different SiO2 /Al2 O3 ratios for 4 days crystallization. Using a SiO2 /Al2 O3 ratio of 32.4, the pattern reveals the co-existence of mordenite (MOR) according to known results of competing phase in SUZ-4 synthesis [2,21] whereas a ratio of SiO2 /Al2 O3 = 16.3 shows a merlinotie (MER) and alpha quartz phase co-existing with SUZ-4. However, with SiO2 /Al2 O3 = 21.2, a high purity SUZ-4 zeolite can be achieved (Fig. 1b). The result shows that the chemical composition of the mixture is very sensitive for SUZ-4 synthesis. It was also observed that gel mixtures with a high SiO2 /Al2 O3 ratio were very viscous and, as the ratio was decreased, the mixtures became less viscous. SEM images of SUZ-4 zeolite obtained after 4 days crystallization are shown in Fig. 2. The images illustrate that most of the crystals are needle-shaped, confirming the formation of SUZ-4 [7,12,22]. However, in Fig. 2c (SiO2 /Al2 O3 = 16.3) some irregularly shaped crystals can be observed. These crystals are the MER and the alpha quartz phase as mentioned earlier. It thus appears that the images found at a higher SiO2 /Al2 O3 ratio gave larger needle-shaped crystals than that obtained at a low ratio (see Table 2). Fig. 1. XRD patterns of SUZ-4 crystals prepared at 155 ◦ C for 4 days with different SiO2 /Al2 O3 ratios: (a) 32.4, (b) 21.2, and (c) 16.3.
chemical bonds (functional groups). The spectral resolution was 4 cm−1 and 256 scans were coded into the mid-infrared region (4000–400 cm−1 ) [23]. 3. Results and discussion 3.1. Using chemical sources for SUZ-4 zeolite synthesis 3.1.1. Effect of SiO2 /Al2 O3 ratios For these experiments, the crystallization reaction time was studied for two conditions: 2 days and 4 days. Fig. 1 shows XRD
3.1.2. Effects of temperature and time of crystallization Two days crystallization time was carried out in the same type of autoclave to confirm the characterization results. However, a higher reaction temperature of 169 ◦ C was controlled in the reactor. Fig. 3 shows XRD patterns with different SiO2 /Al2 O3 ratios for 2-day crystallization. SUZ-4 zeolites were mainly obtained from SiO2 /Al2 O3 ratios of 32.7 and/or 21.2. Using a SiO2 /Al2 O3 ratio of 32.7 still gave some impurities of MOR, and SiO2 /Al2 O3 = 16.2 has been shown to have competing MER, alpha quartz and phillipsite (PHI) phases as product impurities of product according to the results of Gujar and Price [21,22]. A gel mixture of SiO2 /Al2 O3 = 21.2 still gave, under experimental conditions, a good sample of pure synthesized SUZ-4 zeolite. These results are in good agreement with previous reports [6,22]. Moreover, the formation of SUZ-4 zeo-
Fig. 2. SEM micrographs of SUZ-4 crystals prepared at 155 ◦ C for 4 days with different SiO2 /Al2 O3 ratios: (a) 32.4, (b) 21.2, and (c) 16.3.
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Table 2 BET surface area and pore volume of zeolites with different synthesis time and SiO2 /Al2 O3 ratios. Synthesis time (days)
SiO2 /Al2 O3
BET surface area (m2 /g)
Micropore volumea (cm3 /g)
Total pore volumeb (cm3 /g)
Pore diameterc (Å)
Crystallite size d
4
32.4 21.2 16.3
107.0 440.4 145.2
0.0269 0.1089 0.0332
0.1657 1.0360 0.1923
5.4 ± 1.0 5.4 ± 1.0 4.6 ± 0.4
0.09 m dia. × 0.63 m long 0.07 m dia. × 0.64 m long 0.09 m dia. × 1.20 m long
2
33.3 21.2 16.2
76.0 347.6 18.4
0.0071 0.0558 -
0.1441 0.3692 0.1046
5.4 ± 0.6 5.4 ± 1.0 4.6 ± 0.5
0.15 m dia. × 1.09 m long 0.10 m dia. × 0.41 m long 0.12 m dia. × 1.23 m long
a b c d
t-Plot micropore analysis method. MP micropore analysis method at P/P0 close to unity. SF micropore analysis method. Measured from SEM micrographs.
lite is here found to be achieved under the narrow range conditions [22]. The formation of SUZ-4 can be confirmed by the SEM images (Fig. 4) that show needle-shaped crystals of SUZ-4 obtained after 2 days crystallization. The images show that most crystals are needle-shaped. However, the image for SiO2 /Al2 O3 = 16.2 shows some irregular shapes and aggregated crystals, which have been in line with XRD pattern of MER, alpha quartz and phillipsite (PHI) phases shown in Fig. 3. The image clearly shows that, similar to the results of 4 days crystallization, the larger needle-shaped crystals were attained from samples with a higher SiO2 /Al2 O3 ratio. In addition, specific surface areas and pore volumes at different SiO2 /Al2 O3 molar ratios and crystallization times were characterized by BET N2 -adsorption/desorption isotherms, as shown in Table 2. The results clearly demonstrate that a gel mixture composition with a SiO2 /Al2 O3 ratio of 21.2 exhibits a high surface area of 440.45 m2 /g and large total pore volume (1.036 cm3 /g) at P/P0 = 1. Under the conditions employed in the experiments here, synthesis of the most pure SUZ-4 occurred for SiO2 :Al2 O3 ratio of 21.2 after 4 days crystallization at 155 ◦ C under autogenous pressure. This product clearly exhibits a high BET surface area and a total pore volume with a narrow pore size distribution. The overall results obtained here suggest that SUZ-4 synthesis is very sensitive to the gel chemical composition of mixture, the temperature and the crystallization time, since MOR and PHI are common competing phases.
3.1.3. Effect of different copper loadings and thermal stability The composition 7.9K2 O:Al2 O3 :21.2SiO2 :2.6TEA2 O:499H2 O was prepared for determination of the effects of Cu loading and thermal stability of Cu-loaded SUZ-4. As determined by XRF analysis, the chemical compositions of Cu-loaded with different weight percentages are summarized in Table 3 the results show that all Cu2+ /SUZ-4 have Si/Al ratio (by weight) in the range of 7.3–8.3. XRD patterns of the K+ /SUZ-4 and different Cu loading are shown in Fig. 5. There is no detectable change in the background due to degradation of the sample, as well as no detectable formation of CuO in the XRD patterns of Cu2+ /SUZ-4. The detection limit of XRD is normally 3–5 wt.%, but with favorable scattering properties, the minimal amount could be close to 1 wt.%. It is possible that the corresponding peaks of CuO might be below the detection limit of this technique. However, even at a maximum Cu loading of 5.5% that is higher than the detection limit of XRD, no CuO peak was detected. Additionally, the decrease of potassium content shown in Table 3 confirms the success of ion exchange between K+ and Cu2+ . Fig. 6 presents the XRD patterns of Cu2+ /SUZ-4 after being treated at different temperatures. The results reveal that Cu loading and thermal treatment did not alter the SUZ-4 structure. BET surface area and total pore volume of Cu-loaded SUZ-4 are summarized in Table 4. With a high weight percentage of Cu loading, the BET surface area of Cu2+ /SUZ-4 increased, except at 2.8% loading. This is probably due to the use of different scaledup batches for 2.8% Cu loading, which may lead to incomplete ion exchange. Fig. 7 shows the FTIR spectrum in the region of 4000–400 cm−1 for K+ /SUZ-4 and Cu2+ /SUZ-4 at 155 ◦ C crystallization for 4 days with SiO2 /Al2 O3 = 21.2. Frequencies of Si(OH)Al group vibration in zeolites depend generally on local structure and composition. The peaks at 3500 cm−1 and 1682 cm−1 are assigned to isolated silanol groups (Si–OH) and absorption O–H stretching, respectively [16,17]. The peaks at 831 and 1103 cm−1 are assigned to the vibration of Al–O–Si and Si–O stretching, respectively. The vibration of Si–O bending for Si–O–Al and Si–O–Si are located at 573 cm−1 and 470 cm−1 , respectively. There is no IR spectroscopic evidence for the presence of CuO after Cu loading. For all samTable 3 Chemical compositions of Cu-loaded with different weight percentages on SUZ-4 zeolite (wt.% Cu2+ /SUZ-4) using XRF analysis.
Fig. 3. XRD patterns of zeolite SUZ-4 crystals prepared at 168 ◦ C for 2 days with different SiO2 /Al2 O3 : (a) 32.7, (b) 21.2, and (c) 16.2.
Element
K+ /SUZ-4
Cu loading 2.3 wt.%
2.8 wt.%
3.3 wt.%
5.5 wt.%
Si K Al O Cu Fe Others
32.89 17.48 4.48 45.07 0 0.07 0.01
33.00 13.37 4.40 54.73 3.90 0.06 0.02
33.42 12.79 4.04 45.94 3.68 0.07 0.06
32.89 12.17 4.47 45.26 5.11 0.07 0.03
33.03 11.58 4.44 45.36 5.51 0.06 0.02
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Fig. 4. SEM micrographs of zeolite SUZ-4 crystals prepared at 168 ◦ C for 2 days with different SiO2 /Al2 O3 : (a) 33.3, (b) 21.2, and (c) 16.2.
Fig. 5. XRD pattern of different Cu loadings Cu2+ /SUZ-4: (a) K+ /SUZ-4, (b) 2.3 wt.% Cu2+ /SUZ-4, (c) 2.8 wt.% Cu2+ /SUZ-4, (d) 3.3 wt.% Cu2+ /SUZ-4, and (e) 5.5 wt.% Cu2+ /SUZ-4.
Fig. 6. XRD patterns of fresh/treated Cu2+ /SUZ-4 prepared with different thermal treatments: (a) fresh Cu2+ /SUZ-4, (b) 400 ◦ C, (c) 500 ◦ C, (d) 600 ◦ C, and (e) 700 ◦ C.
Table 4 BET surface area with different weight percentages of Cu2+ /SUZ-4. Cu loading (wt.%)
BET surface area (m2 /g)
External surface areaa (m2 /g)
Micropore volumea (cm3 /g)
Total pore volumeb (cm3 /g)
Pore diameterc (Å)
2.3 2.8 3.3 5.5
341.9 300.9 345.2 398.3
232.8 182.3 229.4 267.8
0.0738 0.0861 0.0730 0.0846
0.5199 0.3965 0.6641 0.6885
5.8 5.7 5.7 5.7
a b c
t-Plot micropore analysis method. MP micropore analysis method at P/P0 close to unity. SF micropore analysis method.
± ± ± ±
0.8 0.9 1.0 0.9
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Fig. 8. XRD patterns of prepared BA and synthesized product prepared with different BA: silica sol molar ratios (a) 0:100, (b) 25:75, (c) 50:50, and (d)100:0. Fig. 7. FTIR-spectra of (a) K+ /SUZ-4, (b) 2.3 wt.% Cu2+ /SUZ-4, (c) 2.8 wt.% Cu2+ /SUZ-4, (d) 3.3 wt.% Cu2+ /SUZ-4, and (e) 5.5 wt.% Cu2+ /SUZ-4.
3.2. Bagasse ash as a silica source for SUZ-4 synthesis
ples of Cu loadings, no vibration was observed at 410, 500 and 610 cm−1 , which correspond to the presence of CuO [24–26]. The result shows that no CuO was formed and it might be concluded that only ionic Cu was formed after ion-exchange with the SUZ-4 zeolite. This is in line with XRD pattern that shows no CuO phase in Fig. 5. Nonetheless, one also should keep in mind that the amount of CuO (if formed) might be too small to be detected by the FTIR.
The BA used in this study is composed of 96.1% silica, 2.98% alumina (Al2 O3 ), 0.77% potassium oxide (K2 O), and trace amounts of other metal oxides. The silica in BA is in amorphous form as confirmed by the XRD (Fig. 8). The BA was used as silica source for SUZ-4 zeolite synthesis under autogenous pressure using a stainless steel autoclave at 150 ◦ C; crystallization lasted 4-days. The gel composition of 7.92K2 O:Al2 O3 :21.2SiO2 :2.6TEA2 O:499H2 O was prepared with different BA: silica sol molar ratios (0:100, 25:75, 50:50 and
Fig. 9. SEM micrographs of as-synthesized SUZ-4 with different molar ratios of BA: silica sol (a) 0:100, (b) 25:75, and (c) 50:50.
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Table 5 BET surface area with different BA: silica sol ratios. Silica from BA: silica sol
BET surface area (m2 /g)
External surface areaa (m2 /g)
Micropore volumea (cm3 /g)
Total pore volumeb (cm3 /g)
Pore diameterc (Å)
0:100 25:75 50:50
402.8 351.2 261.7
291.9 200.9 148.8
0.0768 0.1081 0.0812
0.6113 0.4365 0.2859
5.7 ± 0.8 5.8 ± 0.8 5.7 ± 0.9
a b c
t-Plot micropore analysis method. MP micropore analysis method at P/P0 close to unity. SF micropore analysis method.
100:0). XRD patterns of the synthesized products with different BA amounts are presented in Fig. 8. The corresponding phases were identified by comparison with the reported standard patterns [7,22,27]. It is evident that when BA was added into the silica sol, the height of the corresponding peaks of SUZ-4 decreased and MER, PHI, and Linde Type F [28,29] were formed when the only silica source used was BA (100:0). The Si/Al ratios of the impurities formed (i.e., 1.9, 2.6 and 1.0, for MER, PHI and Linde Type F, respectively) are much lower than that of SUZ-4 (Si/Al = 6.2) [21]; this implies that formation of the competing phases requires less silica than SUZ-4. It should be highlighted that, in this study, BA was used as amorphous solid, while the silica sol was in the form of colloidal solution. Thus, the BA required a longer time to be dissolved completely to form silicate units, compared to the time required silica sol (which has a higher activity). Moreover, zeolite crystallization is a competitive reaction depending on the controlled conditions and on the nature of each chemical species involved. Therefore, when BA alone was used as a source of silica, the availability of silicate units was quite limited and favored the formation of MER, PHI and Linde Type F instead of the SUZ-4 zeolite. It is worth mentioning that the impurities of other compounds in prepared BA may affect on the formation of the SUZ-4. These results are in good agreement with those of Gujar et al. [7], who reported that SUZ-4 formation occurred in a narrow range of conditions and was very sensitive to various factors. SEM micrographs of the products were taken as shown in Fig. 9. The pictures confirm the formation of SUZ-4 as needle-shaped crystals. It is also found that the crystal of SUZ-4 was approximately 0.07 m in diameter and 0.61 m long; these results are close to those for SUZ-4 synthesized from a chemical source at a SiO2 /Al2 O3 ratio of 21.2 after 4-days, as shown in Table 2 (0.07 m dia. × 0.64 m long). ˚ this The mean size of obtained SUZ-4 is approximately 5.7 A; is the size of the open channel inside the SUZ-4 structure [3]. The surface area, the micropore volume, and the total pore volume of the products were also analyzed and are summarized in Table 5. The results clearly show that the surface area and pore volume are directly related to the amount of SUZ-4 formed. With increasing BA contents, the surface area and pore volume decrease as the result of the formation of impurities. 4. Conclusions SUZ-4 zeolites have been successfully synthesized under different conditions. With TEAOH as a structure directing agent, a good sample of synthesized SUZ-4 zeolite can be produced from a gel mixture of SiO2 /Al2 O3 = 21.2 under autogenous pressure using a stainless steel autoclave at 150 ◦ C for 4 days. Different BA:silica sol ratios did change the purity of the obtained SUZ-4. The differences in crystal size, specific surface areas, pore volume and pore size distribution have been reported. Copper (II) loading did not change the SUZ-4 zeolite structure, and no CuO formation was found. Increasing the content of BA to 50%, a high purity of SUZ-4 was still obtained with 262 m2 /g surface area is. Using more BA together with silica
sol, mono-distribution of pores having a mean size of approximately 5.7 A˚ was obtained. When 100% BA was added, competing phases (MER, PHI and Linde Type F) were formed, and no SUZ-4 zeolite was found. From this study, we conclude that bagasse ash can be used as co-silica-source for SUZ-4 synthesis, thus allowing the use of some bagasse waste. More studies however are required to fully access its range of applications and its economical limitations. Acknowledgements The authors gratefully acknowledge the financial support of Thailand Research Fund (TRF) under grant number MRG5280110 and TRF-master research grants and Khonburi Sugar Company Limited under grant number MRG-WI525E092. We also acknowledge the grant for research publications (Amarin Phatruk) from the Graduate School Kasetsart University and research grants from the Kasetsart University Research and Development Institute (KURDI) and the Commission on Higher Education, Ministry of Education, the “National Research University Project of Thailand (NRU)”. References [1] International Zeolite Association, Database of Zeolite Structures, http://www. iza-structure.org/databases (accessed 10.05.2010). [2] S.A. Barri, Crystalline (Metallo) Silicates and Germanates-SUZ-4, United States, 5,118,483, 1992. [3] S.L. Lawton, J.M. Bennett, J.L. Schlenker, M.K. Rubin, Synthesis and proposed framework topology of zeolite SUZ-4, J. Chem. Soc., Chem. Commun. 11 (1993) 894–896. [4] W.C. Paik, C.H. Shin, J.M. Lee, B.J. Ahn, S.B. Hong, Host–guest interactions in P1, SUZ-4, and ZSM-57 zeolites containing N,N,N,N ,N N hexaethylpentanediammonium ion as a guest molecule, J. Phys. Chem. B 105 (2001) 9994–10000. [5] K.G. Strohmaier, M. Afeworki, D.L. Dorset, The crystal structures of polymorphic SUZ-4, Z. Kristallogr. 221 (2006) 689–698. [6] P. Worathanakul, P. Kongkachuichay, New SUZ-4 zeolite membrane from sol–gel technique, Int. J. Chem. Biomol. Eng. 1 (2008) 131–135. [7] A.C. Gujar, A.A. Moye, P.A. Coghill, D.C. Teeters, K.P. Roberts, G.L. Price, Raman investigation of the SUZ-4 zeolite, Micropor. Mesopor. Mater. 78 (2005) 131–137. [8] S. Bhattacharyya, R.K. Das, Catalytic reduction of NOx in gasoline engine exhaust over copper-and nickel-exchanged X-zeolite catalysts, Energy Convers. Manage. 42 (2001) 2019–2027. [9] A.E. Palomares, F. Marquez, S. Valencia, A. Corma, On the researching of a new zeolite structure for the selective catalytic reduction of NO: the possibilities of Cu-exchanged IM5, J. Mol. Catal. A: Chem. 162 (2000) 175–189. [10] C. Torre-Abreu, C. Henriques, F.R. Ribeiro, G. Delahay, M.F. Ribeiro, Selective catalytic reduction of NO on copper-exchanged zeolites: the role of the structure of the zeolite in the nature of copper-active sites, Catal. Today 54 (1999) 407–418. [11] A. Subbiah, B.K. Cho, R.J. Blint, A.C. Gujar, G.L. Price, J.E. Yie, NOx reduction over metal-ion exchanged novel zeolite under lean conditions: activity and hydrothermal stability, Appl. Catal., B 42 (2003) 155–178. [12] M.A. Asensi, M.A. Camblor, A. Martinez, Zeolite SUZ-4: reproducible synthesis physicochemical characterization and catalytic evaluation for the skeletal isomerization of n-butenes, Micropor. Mesopor. Mater. 28 (1999) 427–436. [13] H. Choo, S.B. Hong, L. Keven, Comparative ESR and catalytic studies of ethylene dimerization on Pd(II)-exchanged clinoptilolite, mordenite, ferrierite, and SUZ4, J. Phys. Chem. B 105 (2001) 7730–7738. [14] S. Jiang, Y.K. Hwang, S.H. Jhung, J.-S. Chang, J.-S. Hwang, Zeolite SUZ-4 as selctive dehydration catalyst for methanol conversion to dimethy ether, Chem. Lett. 33 (2004) 1048–1049. [15] S.-H. Lee, C.-H. Shin, G.J. Choi, T.-J. Park, I.-S. Nam, B. Han, S.B. Hong, Zeolite synthesis in the presence of flexible diquaternary alkylammonium ions (C2 H5 )3 N+ (CH2 )N+ (C2 H5 )3 with n = 3–10 as structure-directing agents, Micropor. Mesopor. Mater. 60 (2003) 237–249.
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