High-silica zeolite Beta (BEA) has three-dimensional intersected channels and 12-membered ring pore openings [1, 2][Newsam, 1988 #1327]. These properties make it useful as a catalyst in aromatic alkylation, isomerization, alkene hydration, aromatic acylation, and nitration syntheses in petrochemical industries [3, 4, 5, 6, 7, 8, 9].
Formation of the zeolite Beta structure was achieved originally using tetraethylammonium hydroxide (TEAOH) as an organic structure-directing agent (OSDA) [10]. However, its use has increased the zeolite Beta cost significantly, thereby limiting its industrial application. For this reason, recent studies related to zeolite Beta have focused mainly on low-cost synthesis using more affordable OSDAs such as tetraethylammonium bromide (TEABr) [11, 12, 13, 14]. Xie et al. [15] demonstrated for the first time that zeolite Beta could be synthesized by adding calcined nanocrystalline zeolite Beta seeds into OSDA-free aluminosilicate gel. This synthesis route attracted much attention [16, 17, 18, 19, 20, 21, 22, 23]. Iyoki et al. [22, 23] proposed that the key factor in successful zeolite synthesis in the absence of OSDA was the common composite building unit contained in both the seeds and zeolite obtained from the gel after heating without seeds. Majano et al. [16] showed that zeolite Beta could be obtained at low crystallization temperature with non-calcined seeds. They believe that the active surface of the as-synthesized seeds promoted crystallization while calcination of the seeds would be harmful because of seed surface deactivation. Kamimura et al. [17, 18] reported that zeolite Beta synthesized with OSDA-free gel could be used as a seed to generate more zeolite Beta. They concluded that the seed was partially dissolved during the initial stage in the hydrothermal environment and that subsequent crystallization took place on the surface of the residual Beta seeds exposed to the liquid. They also observed that zeolite Beta with SiO2/Al2O3 ratio greater than 52 could not be used as seeds because of their complete dissolution in the initial stage in the hydrothermal environment. Xie et al. [19] showed that the residues partially dissolved Beta seeds rather than the dissolved species of Beta seeds helped crystallization. They proposed a core-shell growth mechanism to describe the crys tallization of OSDA-free gel on the surface of partially dissolved Beta seeds.
Although it is well known that seeding is useful for the synthesis of many zeolites, the mechanism by which this occurs has been interpreted in various ways: some believe that seeds behave as crystal nuclei supplying a surface for the crystallization of amorphous aluminosilicate gel; others suggest that the seeds dissolve partially and then the residual seed, or dissolved species, or both form nuclei [23, 24]. An investigation into the seeding mechanism therefore holds significance not only for OSDA-free synthesis of zeolite Beta but also for improving synthesis techniques of other zeolites.
In this work, we carried out a detailed study on the OSDA-free synthesis of zeolite Beta using different seeds. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet (UV)- Raman spectroscopy were used to characterize the solid products obtained before and during the synthesis. Emphasis was given to the structure-directing effect of different seeds, key aspects of the seed that influence the structure-directing effect, and the seeding mechanism.
Al-containing zeolite Beta seeds were synthesized as follows. First, silica sol (SiO2, 30 wt%, Qingdao Haiyang Chemical Co.) or fumed silica (Shenyang Chemical Co.) was mixed with OSDA solutions, which included a TEAOH solution (20 wt%, Hejian Qingfeng Shimian Chemical Co.), TEABr solution (99 wt%, Jintan Huadong Chemical Research Institute), ammonia and NaOH, or solution of TEABr and TEAOH. A NaAlO2 solution (Al2O3, 41 wt%, Sinopharm Chemical Reagent Co.) was added to the mixture with vigorous stirring for 40 min. The mixture was transferred to an autoclave and crystallized at 145 °C under static or stirred conditions for ~3-6 d.
Pure silica zeolite Beta seed was synthesized as follows. Fumed silica was mixed with the TEAOH solution (40 wt%, condensed in laboratory). Next, NH4F was added and the mixture stirred thoroughly. The sticky gel obtained was placed in a Teflon-lined stainless steel autoclave and crystallized at 150 °C for 4 or 5 d.
All solid products were filtered, washed, dried overnight at 110 °C, and calcined in air at 540 °C for 6 h to remove the OSDA before they were used as seeds.
A gel with molar composition Na2O:Al2O3:SiO2:H2O = 11.4:1:40:640 was prepared as follows. Fumed silica was dissolved in the NaOH solution before addition of the NaAlO2 solution under vigorous stirring. Calcined zeolite Beta was then added as seed (10 wt% in relation to silica source). The mixtures were agitated to form a homogenous gel. The gel was transferred into a 100-ml autoclave and crystallized statically at 140 °C. Sampling was conducted at time intervals. The solid product was isolated from the resultant mixture by filtration, washed with deionized water, and dried at 110 °C for characterization.
XRD patterns were collected on a Rigaku D/max-2004 diffractometer using Cu Kα radiation (40 kV, 100 mA) and a scanning rate of 0.02°/min (2θ). The crystallinity of the obtained Beta phase was calculated based on the intensity of the peak at reflection (3 0 2) (2θ = ~22.4°).
FE-SEM micrographs were recorded on a Hitachi S-4800 microscope. TEM micrographs were obtained on a JEOL JEM-2100 electron microscope operating at 200 kV with a point resolution of 0.23 nm. TEM samples were dispersed in ethanol and a droplet of this mixture was deposited on a Cu grid.
FT-IR spectra in the hydroxyl region were obtained on a Nicolet iS10 FTIR instrument according to the following procedure. The sample was pressed into a self-supporting wafer and placed into a quartz IR cell with CaF2 windows. The FT-IR spectra were recorded with a resolution of 4 cm−1 at room temperature. Prior to measurement, the sample was dehydrated under vacuum at 400 °C for 4 h.
UV-Raman spectra were recorded on a DL-2 Raman spectrometer. The 244-nm line of a LEXEL LASER was used as the excitation source. An Acton triple monochromator was used as a spectrometer for Raman scattering. Spectra were collected using a Prinston charge-coupled device detector. The power of the laser line at the sample was below 3 mW.
Elemental analyses were performed using a Bruker SRS 3400 X-ray fluorescence spectrometer.
N2 adsorption-desorption isotherms were recorded at -196 °C on a Micromeritics ASAP 2000 instrument after activating the sample under vacuum at 350 °C for at least 6 h. The surface area was evaluated using the BET method. The external surface area, micropore surface area, and micropore volume were calculated using the t-plot method. The total pore volume was determined from the amount adsorbed at a relative pressure of approximately 0.99, and the mesopore volume was calculated from the difference between the total and micropore volume.
To obtain different zeolite Beta seeds, the synthesis of zeolite Beta was carried out in Al-containing and Al-free gels with different silica sources and different OSDA solutions. The resultant seeds were investigated and the main crystal data are summarized in Table 1. Seeds S1 to S6 were less than 200 nm in crystal size with relatively larger mesopore volume owing to aggregation of small crystals. However, they were different in terms of SiO2/Al2O3 ratio and relative crystallinity. Both the SiO2/Al2O3 ratio and relative crystallinity increased from seed S1 to S6. Seeds S7 and S8 were synthesized in the same gel but with different crystallization times. Both were approximately 3-μm spherical crystals and their SiO2/Al2O3 ratios were close to that of seed S5. However, the relative crystallinity of S8 was higher than that of S7 because it was synthesized over longer time. Seeds S9 and S10 were also synthesized in the same gel, with S10 being crystallized over longer time but seeds S9 and S10 were pure silica zeolite Beta approximately 9 μm in crystal size and with truncated octahedral morphology. It is worth noting that the relative crystallinity of the seeds calculated from XRD and micropore volume (Vmicro) data was almost the same for S1 to S6 but different for S7 to S10. Differences in seeds S7 to S10 may be caused by crystal size and lattice imperfections [25, 26]. In seeds S7 and S8, the microcrystals were composed of nanocrystals while in seeds S9 and S10, the large crystals were all monocrystals. The crystal size may result in weak XRD peaks in S7 and S8 and strong ones in S9 and S10. FE-SEM micrographs also show that seed S10 and especially seed S9 had high-density wormhole defects (not shown), which may result in a decrease of micropore volume for S9 and S10.
The OH vibration FT-IR spectra are shown in Fig. 1. Generally, the typical zeolite Beta may exhibit six bands, including hydroxyls on a partially hydrolyzed framework Al (3783 cm−1), terminal SiOH (3745 cm−1), internal SiOH at framework defects (3735 cm−1), hydroxyls associated with extra framework Al (3665 cm−1), bridging hydroxyls (3610 cm−1), and hydroxyl-bonded hydroxyls (broad band at 3400-3700 cm−1) [25, 27]. It can be seen from Fig. 1 that seeds S1 to S8 had bridging hydroxyl peaks at 3610 cm−1, while seeds S9 and S10 did not. This phenomenon confirms that seeds S1 to S8 were Al-containing zeolites and seeds S9 and S10 were pure silica zeolites. The intensities of the 3745 cm−1 band were stronger for seeds S1 to S6, weaker for seeds S7 and S8, and very weak for seeds S9 and S10. This agrees with the fact that seeds S1 to S6 were small crystals while seeds S7 to S10 were large crystals.
The UV-Raman spectra of the seeds are shown in Fig. 2. The most intense Raman scattering of the zeolite Beta framework vibrations appear mainly from 310 to 470 cm−1. According to the literature [28, 29, 30, 31], the peaks at 314 and 343 cm−1 should be assigned to five-membered rings, those at 399 and 425 cm−1 to six-membered rings, and that at 465 cm−1 to four-membered rings. The peaks at 314, 399, and 465 cm−1 belonged to the rings in the periodic building unit, while the peaks at 343 and 425 cm−1 belonged to the interlayer connectivity mode for polymorphs. Therefore, the intensity ratio of peaks at 314 and 343 cm−1 indicated the presence of interlayer connecting faults and the larger value indicated fewer stacking faults. It can be seen that seeds S1 to S8 had a larger but comparable amount of stacking faults while seeds S9 and S10 had the least.
The seeds played a crucial role in the formation of the zeolite Beta structure in the OSDA-free gel because no beta phase could be obtained without seed. Beta zeolites were synthesized by adding different seeds as indicated in Table 2. However, when seeds S1 to S5 were used, the synthesized products (BEA1 to BEA5) showed low zeolite Beta crystallinity. When seeds S6 to S10 were used, the synthesized products (BEA6 to BEA10) showed good zeolite Beta crystallinity. For seeds S1 to S6, which had a similar crystal size (less than 150 nm) but increasing SiO2/Al2O3 ratio, the crystallinity of the synthesized products increased from 16% to 89%. This phenomenon implies that the SiO2/Al2O3 ratio is a very important parameter for zeolite Beta seeding. To carry out the successful OSDA-free synthesis of zeolite Beta, it is better to use zeolite Beta seed with a SiO2/Al2O3 ratio of more than 30. Successful synthesis with pure silica seeds (S9 and S10) in this study implies the possibility of a much higher SiO2/Al2O3 ratio range existing for zeolite Beta seed selection. This opinion is different from previous research that has succeeded in the OSDA-free synthesis of zeolite Beta using zeolite Beta seeds with SiO2/Al2O3 ratios of between 20 and 52 [15, 16, 17, 18, 19, 20]. According to this research, seeds with SiO2/Al2O3 ratio greater than 52 could not provide a beta phase because of complete dissolution. We assume that the dissolution behavior of the high-silica zeolite Beta seed during the OSDA-free synthesis of zeolite Beta may be influenced by its morphological and constructional features, including crystal size and crystal defects.
The crystal size of zeolite Beta seeds affected the crystal size of the synthesized zeolite Beta product. As indicated by Table 2 and Fig. 3, although the zeolite Beta products obtained with different seeds had a similar appearance (intergrown crystals with truncated octahedral morphology), the increase in crystal size of the zeolite Beta seeds resulted in an obvious increase in crystal size of the zeolite Beta product. It is also interesting to note from Fig. 3 that the residual bodies of the larger crystal seeds remained in the obtained zeolite Beta products (BEA8-b and BEA10-b). For the Al-containing large crystal seed (S8), there was an obvious growth of zeolite Beta product on the seed residue surface, as indicated by the crowded small multidimensional faces on the big seed residue (BEA8-b). For the pure silica large crystal seed (S10), however, no growth of zeolite Beta product on the seed residue could be seen. The residue was round and relatively smooth.
Despite these influences, the zeolite Beta products obtained with different seeds all had low but roughly the same SiO2/Al2O3 ratios. The same SiO2/Al2O3 ratio (approximately 10) as well as similar morphology (intergrown crystals with truncated octahedral morphology) imply that the zeolite Beta products obtained in the OSDA-free gels were mainly defined by special hydrothermal conditions.
Figure 4 shows the crystallization curves of OSDA-free gels with different zeolite Beta seeds while the inset shows the solid product yield of zeolite Beta at the early stages of crystallization. The decline in zeolite Beta yield at the early stages of crystallization indicates that all seeds were partially dissolved in the induction period. The decline in zeolite Beta yield for BEA9 and BEA10 indicates that the pure silica seeds could be dissolved to a high degree. The different zeolite Beta seeds influenced the crystallization process in the OSDA-free gels considerably. First, the duration of the induction period was related mainly to the crystal size of the zeolite Beta seeds. The smaller seeds tended to have a shorter induction period while the larger seeds tended to have a longer induction period (Fig. 4(b)). This may be because the smaller seeds generally dissolved faster and so a shorter time was needed for the generation of zeolite Beta nuclei. Second, the growth rate of the zeolite Beta crystal seemed to relate to both the SiO2/Al2O3 ratio and crystal size of the zeolite Beta seeds. By comparing the crystallization curves of BEA1 to BEA6, which were seeded with zeolite Beta (S1 to S6) of largely similar crystal size but different SiO2/Al2O3 ratio, it could be seen that the crystal growth rate as a whole increased moderately with SiO2/Al2O3 seed ratio (Fig. 4(a)). By comparing the crystallization curves of BEA6 to BEA8, which were seeded with zeolite Beta (S6 to S8) of similar SiO2/Al2O3 ratio but different crystal size, it was found that the crystal growth rate decreased significantly as the seed crystal size increased (Fig. 4(b)). Compared with the SiO2/Al2O3 ratio, the crystal size of the seeds had a significant effect on the zeolite Beta crystal growth rate. The influence of crystal size of seeds on the crystal growth rate of zeolite Beta may be attributed to the number of nuclei present. The number of nuclei generated by the different seeds is supposed to decrease with increase in crystal size of zeolite Beta. This assumption is consistent with SEM observations, which indicated that an increase in crystal size of zeolite Beta seeds resulted in an increase in crystal size of zeolite Beta product. Third, the different zeolite Beta seeds also had a strong influence on the stability of the zeolite Beta product under hydrothermal synthesis. For seeds S1 and S2 (corresponding to the BEA1 and BEA2 curves), crystallization ceased at approximately 7 h. Crystal transformation from zeolite Beta to mordenite then took place. Therefore, only low crystallinity zeolite Beta products (lower than 20%) were obtained with these seeds. For seeds S3 to S6 (corresponding to the BEA3 to BEA6 curves), crystallization was extended to 15 to 17 h, and the crystallinity of the zeolite Beta products increased to approximately 50% to 90%. For seeds S7 to S10 (corresponding to the BEA7 to BEA10 curves), a much longer crystallization time was allowed, and the crystallinity of the zeolite Beta products could be increased to more than 90% before crystal transformation occurred (crystal transformation caused a drop-off in crystallinity in the curves). Therefore, in the OSDA-free synthesis of zeolite Beta, the high-silica zeolite Beta seed favors the stability and crystallinity of the zeolite Beta product.
OSDA-free synthesis of zeolite Beta was carried out with calcined seed S7. After calcination, the OSDA molecules in the seed pore channels were removed. The solid products obtained before and during crystallization were characterized by XRD, FT-IR, and FE-SEM.
Figure 5 shows that the gel-containing seed S7 (10 wt%) had a weak diffraction peak of zeolite Beta at 2θ = 22.48°. During the induction period (0-42 h), this diffraction peak shifted to lower 2θ values, which suggests an increase in Al content in the crystal framework (Al−O bond length is larger than that of Si−O). Because the zeolite Beta yield declined in the induction period (Fig. 4(b)), we tend to attribute this peak shift phenomenon to the dissolution of a Si-rich area of seeds under basic hydrothermal conditions. After the induction period, the gel began to crystallize. This peak shifted slowly to 2θ = 22.14° and increased in intensity. This indicates that Al-rich zeolite Beta was obtained.
Figure 6 shows that the initial gel had a strong signal at 3745 cm−1, which is attributed to the terminal SiOH of the gel particles. During the induction period, this band became weak. This change may be an indication of the digestion (or rearrangement) of the amorphous gel under hydrothermal conditions. When the crystallization time was more than 42 h, the solid product showed a new strong absorption peak at 3614 cm−1, which is assigned to bridging hydroxyls. This indicated that a great deal of Al entered the framework during the crystal growth process, which agrees well with the peak shift in the XRD analysis.
Figure 7 shows that in the induction period ((b)-(g)) two important changes occurred to the gel: one was the dissolution of seeds, which seemed to start at the exposed surface and develop towards the inside of the seed balls and the other was the softening of the graining fresh gel and the covering of the tender gel on the seed balls. By the end of the induction period (Fig. 7(f)-(g)), sprout-like crystals could be seen penetrating the gel cover from the surface of the inner seed balls. The well-crystallized product was a mixture of large and small crystals. The small crystals were intergrown with truncated octahedral morphology. The surface of the large crystals was heavily populated with fresh and small zeolite Beta crystals.
The OSDA-free synthesis of zeolite Beta was also studied with other seeds. The TEM micrographs related to the crystallization of seed S3- and S6-containing gels are shown in Fig. 8(a,b), and the SEM micrographs related to the crystallization of seed S9- and S10-containing gels are shown in Fig. 8(c,d). SEM characterization was used for the larger crystal samples as the TEM characterization was unsuccessful.
Figure 8 shows that seed dissolution occurred in all cases except for the crystallization of seed S3-containing gel. The results for seed S3-containing gel may arise because of the low extent of dissolution and small crystal size of seed S3, as the dissolution of seed S3 has been confirmed by the decline of zeolite Beta yield during the induction period (Fig. 4(a)). The situation is similar for seeds S1 to S4. The initial gels underwent a digestion (or rearrangement), which made the amorphous gels soft and sticky, and tender gels covered the seeds. However, differences did exist between the seeds. For example, for most of the Al-containing seeds (such as seed S6), dissolution tended to take place inside the seeds, which resulted in the formation of hollow seed residues. In subsequent crystallization, the hollow seed residue surface served as substrate for the growth of fresh and small zeolite Beta crystals. In contrast, for Al-free large seeds (such as seeds S9 and S10), dissolution occurred on the outside of the seeds, which resulted in their disintegration and the formation of smaller rounded residues. In subsequent crystallization, there was no visible growth of the fresh and small zeolite Beta crystals on the surface of the rounded seed residues.
Based on these observations, we believe that the dissolution of the seeds in the OSDA-free synthesis of zeolite Beta is a common phenomenon although the degree of dissolution and behavior may be different because of differences such as SiO2/Al2O3 ratio and crystal size of the seeds. The seed residues produced by dissolution assumed the structure-directing role in the OSDA-free synthesis of zeolite Beta. In this case, the role of the seed residues is to provide an “immobilized” surface nucleus. The pure silica seed residues, at least, seem to be an exception. The dissolved seed fragments also have an important role in the OSDA-free synthesis of zeolite Beta, as evidenced by the appearance of abundant small crystals in the crystallization products of the large seed-containing gels. The dissolved seed fragments can definitely serve as nuclei. For the pure silica seeds (seeds S9 and S10), the dissolved seed fragments are the main nuclei source. The seeding mechanism is different from that reported to date in the literature. As stated above, Kamimura et al. [18] have concluded that the crystallization of zeolite Beta from the OSDA-free gel took place on the surface of the residual Beta seeds, and that the seed residues should be exposed to the liquid. Xie et al. [19] have shown that it was the residue of partially dissolved Beta seeds rather than the dissolved species of Beta seeds that assisted in the crystallization.
In the non-calcined seeds, the pore channels of the zeolite Beta seeds were expected to be occupied by OSDA molecules. A previous study has shown that the calcined zeolite Beta seed with SiO2/Al2O3 ratio of 52 was unsuccessful in zeolite Beta synthesis from OSDA-free gel but that the same zeolite Beta seed without calcination was successful [16]. When we investigated the influence of pre-calcination with seed S6, it was found that both the calcined and non-calcined zeolite Beta seeds led to successful zeolite Beta synthesis. However, the gel-containing calcined seed showed a higher degree of seed dissolution, shorter induction period, and higher crystal growth rate (Fig. 9). In contrast with the significant inner dissolution of the calcined seed (Fig. 8(a,b)), the non-calcined seed did not show a significant dissolution in the induction period (Fig. 10). These results were different from the previous study, which showed that the active surface of as-synthesized seeds promoted crystallization while the calcination of seeds would be harmful because of the deactivation of the seed surface [16]. Interestingly, for the gel-containing calcined seed, the crystallization products (from 7 to 16 h) gave a singlet characteristic peak of zeolite Beta around 2θ = 22.14° (Fig. 11(a)). For the gel-containing non-calcined seed, however, the crystallization products (from 20 to 33 h) gave a doublet characteristic peak of zeolite Beta in the same region (Fig. 11(b)). The latter case provides evidence of the formation of the core-shell structure of zeolite Beta. The core was the zeolite Beta seed S6 with higher SiO2/Al2O3 ratio, while the shell was the new zeolite Beta with lower SiO2/Al2O3 ratio. These results indicate that pretreatment is an important factor for influencing the structure-directing performance of zeolite Beta seed.
Compared with seeding in a fresh gel, when the same zeolite Beta seed (S7) was added into the aged gel (prehydrothermal treatment of fresh gel for 7 h at the crystallization temperature), more seed was dissolved and the seeding resulted in a shorter induction period and faster crystal growth (Fig. 12). The SEM micrographs (Fig. 13) show that during aging the fresh gel became fused and viscous ((a)-(c)), as was seen in the induction period of the foregoing experiments (Fig. 7). The difference is that when the seed was added into the aged gel, the viscous gel did not envelop the seed. This may be why the seed dissolved more rapidly and in higher quantities. In this case, seed dissolution did not result in the formation of hollow balls as was the case for seeding in a fresh gel (Fig. 7), but appeared to take place on the surface of the seed. At the end of the crystallization, the surface of the seed residues was heavily populated with small fresh zeolite Beta crystals, which formed large crystals. Seeding an aged gel also yielded many small crystals. Once again, this provides evidence for the structure-directing effect of dissolved seed fragments.
The synthesis of zeolite Beta with OSDA-free gel was achieved using several zeolite Beta seeds, which differed mainly in SiO2/Al2O3 ratio and crystal size. However, the different zeolite Beta seeds influenced the crystallization process and product significantly. As the seed SiO2/Al2O3 ratio increased, the induction period was shortened and crystal growth rate was enhanced. However, the effect of the seed crystal size was the opposite and much stronger. The seed with high SiO2/Al2O3 ratio was favorable for the synthesis of zeolite Beta with high crystallinity, while the seed with large crystal size resulted in an increase in product crystal size. Nevertheless, different zeolite Beta seeds all produced zeolite Beta with similar crystal morphology and SiO2/Al2O3 ratio. This indicates that the zeolite Beta products obtained in the OSDA-free gels were mainly determined by special hydrothermal conditions. In the induction period, the different zeolite Beta seeds all underwent dissolution. The increase of seed SiO2/Al2O3 ratio enhanced the extent of dissolution of the seed, while the increase in seed crystal size reduced the dissolution speed. Compared with the as- synthesized seed, precalcined seeds dissolved faster and in higher quantities. Dissolution of the seed commenced on the bare surface of the seed. However, when this surface was enveloped by the sticky gel, the dissolution of the seed likely developed from the tiny bare surface into the inside of the seed, thus forming a hollow seed ball. Morphology studies showed that the seed residues produced by dissolution could provide an “immobilized” surface nucleus, which allowed for the dense growth of fresh small crystals of zeolite Beta although the residues of pure silica seed were an exception. Small seed fragments produced by dissolution could provide dispersed nuclei that resulted in the formation of relatively scattered small zeolite Beta crystals. This may be the main structure-directing technique of the pure silica zeolite Beta seed. The use of precalcined zeolite Beta seed with smaller crystal size and appropriately high SiO2/Al2O3 ratio will be useful in the crystallization of zeolite Beta from OSDA-free gel with high crystallinity and purity.
2014, Vol. 35 Issue (11): 1800-1810
PDF (3175 KB)
2014, Vol. 35 Issue (11): 1800-1810
PDF (3175 KB)