Ultrafast and Continuous Flow Synthesis of Silicoaluminophosphates

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Ultrafast and Continuous Flow Synthesis of Silicoaluminophosphates Zhendong Liu, Toru Wakihara, Naoki Nomura, Takeshi Matsuo, Chokkalingam Anand, Shanmugam P. Elangovan, Yutaka Yanaba, Takeshi Yoshikawa, and Tatsuya Okubo Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b02141 • Publication Date (Web): 14 Jun 2016 Downloaded from http://pubs.acs.org on June 19, 2016

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Chemistry of Materials

Ultrafast and Continuous Flow Synthesis of Silicoaluminophosphates Zhendong Liu,†# Toru Wakihara,†# Naoki Nomura,† Takeshi Matsuo,‡ Chokkalingam Anand,† Shanmugam P. Elangovan,† Yutaka Yanaba,§ Takeshi Yoshikawa,§ Tatsuya Okubo*† †

Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan ‡

Alumina Fiber & Inorganic Products Department, Mitsubishi Plastics, Inc., Tokyo 100-8252, Japan

1-1-1, Marunouchi, Chiyoda-ku,

§

Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8505, Japan

ABSTRACT: Silicoaluminophosphates are a class of crystalline microporous materials that have been widely used as catalysts and adsorbents. Two representative silicoaluminophosphates, SAPO-CHA (also called SAPO-34) and SAPO-AFI (also called SAPO-5), were synthesized in a tubular reactor within 10 min and 5 min, respectively. The addition of a milled seed with small crystal size, the pretreatment of Al and Si sources by mechanical milling and the employment of high temperature condition were found to be the critical factors that contributed to the enhancement of crystallization rate of SAPOCHA. The fast synthesized SAPO-CHA possesses only isolated Si(OAl)4 species, indicating a great potential in catalytic applications. SAPO-CHA and SAPO-AFI usually appear as a pair of competing phases during the synthesis of SAPOCHA/SAPO-AFI because of similarities in chemical compositions and formation conditions. Here we show that owing to the feature of rapid heating, the tubular reactor demonstrated itself as a facile and precise platform to control over the phase selection between SAPO-CHA and SAPO-AFI by tuning the crystallization kinetics, which could not be realized in the conventional autoclaves. A continuous flow process was also established to synthesize these two silicoaluminophosphates with high efficiency and flexibility. These results demonstrate a comprehensive strategy to achieve the minute-order synthesis of two important silicoaluminophosphates, and could be very useful to direct the ultrafast synthesis of other crystalline materials.

Introduction Zeolites, a class of crystalline microporous aluminosilicates built upon tetrahedral Al and Si atoms, have played an important role in the fields of catalysis and separation.1-3 The emergence of phosphate-based zeolites, including aluminophosphates and silicoaluminophosphates, enormously enriched framework versatility and chemical diversity of crystalline microporous materials.4-6 Up to date, 231 zeolite framework structures have been identified.7 Aluminophosphates are composed of tetrahedral Al and P atoms in an exactly alternative manner. Unfortunately, due to structural instability, the applications of aluminophosphates are very limited. On the contrary, incorporation of Si atoms into the framework of aluminophosphates generates silicoaluminophosphates, which possess high structural stability as well as ion exchange capability that results in Brønsted acidity and redox activity.8 Silicoaluminophosphates therefore draw special attention because of their wide applications arising from unique properties with respect to aluminosilicates and aluminophosphates. SAPO-CHA (also called SAPO-

34), a silicoaluminophosphate with CHA topology, has proven to be able to exhibit excellent activity and selectivity in a series of catalytic reactions, such as transformation of methanol to light olefin (MTO),9-11 selective conversion of syngas to light olefin,12 direct conversion of ethylene to propylene (ETP)13,14 and ammonia selective catalytic reduction (NH3-SCR) of nitrogen oxides (NOx).15-18 SAPOAFI (also called SAPO-5), a silicoaluminophosphate with AFI topology, can be potentially used as a catalyst in chemical reactions such as isopropylation of benzene and alkylation of toluene.19-21 Meanwhile, silicoaluminophosphates possess a subtle balance between hydrophilicity and hydrophobicity, and therefore are suitable to be used as water adsorbents. For example, SAPO-CHA is an excellent water vapor adsorbent for adsorption heat pump with high adsorption-desorption circle durability, and therefore provides an efficient route to utilize waste heat.22-24 These important applications have stimulated intensive studies on silicoaluminophosphates. Therefore, developing an efficient route to prepare highquality silicoaluminophosphate materials is of high significance.

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The synthesis procedure of silicoaluminophosphate is similar to that of aluminosilicate zeolites. Crystallization mechanism of silicoaluminophosphate, however, is viewed to be different.4-6 Crystallization of silicoaluminophosphate is largely interpreted in terms of substituting Si atoms into a corresponding aluminophosphate framework. The formation of the aluminophosphate framework undergoes a unique pathway evolving from one-dimensional chain to twodimensional porous layer and finally to three-dimensional framework.25,26 While for silicoaluminophosphate, the incorporation of Si atoms into the chain or layer structures follows via substitution mechanisms including one silica atom replaces one P atom (SM2) and two silica atoms replace neighboring P and Al atoms (SM3).27,28 These substitution mechanisms result in different Si coordination environments (including Si(OSi)n(OAl)4-n, n=0, 1, 2, 3 and 4) , which consequently bring about huge difference in the properties of the products. Excess Si incorporation due to SM3 substitution mechanism may result in the formation of Si island, which denotes the Si(OSi)4 species. Si island has proven disadvantageous to the catalytic performance of SAPO-CHA, as these Si-rich species do not create negative charges and thus lack the capability to stabilize the extra-framework cations.29,30 Organic structure-directing agent (OSDA) has been found to play a vital role in effecting the Si coordination. For example, a synthesis using tetraethylammonium hydroxide (TEAOH) is more likely to generate SAPO-CHA with Si island,31,32 whereas the employment of mixed OSDAs or a single OSDA with specifically designed properties can optimize Si distribution, avoiding the formation of Si island.33-35 Moreover, SAPO-CHA and SAPO-AFI always appear as a pair of competing phases during the synthesis of SAPOCHA/SAPO-AFI because of similarities in chemical compositions and formation conditions, and many delicate efforts have been devoted to optimize the synthesis parameters to obtain a pure phase. These aspects should be considered to develop an ultrafast route for the synthesis of high-quality silicoaluminophosphates. Recently, we have developed a minute-order synthesis route to prepare crystalline microporous materials, with which several representative zeolite materials, including aluminophosphate AlPO4-5 (within 1 min),36 high-silica zeolite SSZ-13 (within 10 min)37,38 and pure-silica zeolite silicalite-1 (within 10 min),39 have been successfully synthesized. On the basis of the ultrashort synthesis period, the continuous flow syntheses of AlPO4-540 and SSZ-1337 have also been demonstrated. Yet, only limited cases have been reported so far, and the applicability of this methodology is still subject to examination. A question then arises as whether this minute-order synthesis method can be applied to silicoaluminophosphates, because these materials are supposed to undergo a unique crystallization mechanism. Following our methods, Sun et al. recently reported the ultrafast synthesis of SAPO-CHA, yet the critical factors to the ultrafast synthesis were not examined in detail.41 The objective of the present work aims at investigating the

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ultrafast syntheses of SAPO-CHA and SAPO-AFI, two representative and industrially important silicoaluminophosphates. Particular considerations were made in order to achieve the ultrafast syntheses of SAPOCHA and SAPO-AFI with high yield, which will be discussed systematically in the following paragraphs. In addition, the fast-synthesized SAPO-CHA proved to possess only isolated Si(OAl)4 species without Si island, and thus has great potential to be used as an excellent catalyst due to high hydrothermal stability and proper acidity. We also demonstrate that phase selection between SAPO-CHA and SAPO-AFI can be tuned by precisely controlling the crystallization kinetics in the tubular reactor. These phenomena have never been observed in the previous studies and would be very helpful to deepen the understanding of the crystallization of silicoaluminophosphates.

Experimental Section Materials: Fumed silica (Aerosil 2000) and pseudoboehmite (Catapal C1) were used as purchased without any further purification. A reference SAPO-CHA seed was provided by Mitsubishi Plastics, Inc. Deionized water made from a Millipore water purification system was used in all experiments. Silicone oil (KF968-1-100, Shin-Etsu Silicone) was used as a heating medium. The tubular reactor (Figure S1) was made from a standard stainless steel tube (1/4 inch, with an inner diameter of 4.4 mm). With a length around 13.5 cm, the tubular reactor was sealed using stainless steel caps (Swagelok, 1/4 inch, SS-400-C) at its two ends. Preparation of the Milled SAPO-CHA Seed: Milling of the reference SAPO-CHA was conducted on a bead milling apparatus (LMZ05, Ashizawa Finetech Ltd., Japan) using ZrO2 as beads (size of the beads: 300 μm). Typically, 10 g of reference SAPO-CHA was dispersed in 250 g pure water to get a slurry, which was then fed by a gear pump into the milling chamber, where the beads were rotating at a rate of 3000 rpm. After a certain period of milling, the milled slurry was collected and dried to obtain the milled SAPO-CHA seed. Preparation of the Milled Al & Si Source: Similarly, fumed silica and pseudoboehmite with a specific ratio were dispersed in pure water to get a slurry. This slurry was treated on the milling apparatus for 30 min, and the milled slurry was collected and dried to obtain the milled Al & Si source. Original Procedure to Prepare the Synthesis Precursor: Using the original procedure, the synthesis precursor was prepared according to the references.24,42 Modified Procedure to Prepare the Synthesis Precursor: Using the modified procedure, the synthesis precursor was prepared as follows: the milled Al & Si sources were added to a phosphoric acid solution and stirred for 3 h upon which organic structure-directing agents were added in sequence and stirred for another 1.5 h to obtain the synthesis precursor with the same composition shown above. Ultrafast Synthesis Using the Tubular Reactor: The synthesis precursor was aged at 90 oC for 24 h. Prior to the


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synthesis at elevated temperatures, 10 wt% SAPO-CHA seed based on Al2O3 was added for a seed-assisted synthesis. Subsequently, 1.5 ml synthesis precursor was transferred to the tubular reactor, which was then sealed and immersed in an oil bath preheated to a certain temperature. After a specific synthesis period, the tubular reactor was quenched in water. The slurry was recovered, centrifuged, washed and then dried overnight at 80 oC to get the final product. Continuous flow synthesis: The following devices were used to set up the continuous flow apparatus: high pressure syringe pump (Micro Feeder JP-H, Furue Science, Japan); HPLC pump (MP311, Lab-Quatec, Japan); back pressure regulator (TESCOM 26-1700, Emerson, US); relieve valve (SS-4R3A, Swagelok). The continuous flow reactor was made from standard stainless tube with an outer diameter of 1/4 in, which was place inside the oil bath with the temperature preset at 210 oC. All parts were connected using Swagelok standard unions, and a homemade system for pressure recording and alarm was installed for safety considerations. The residence time was adjusted by controlling the flow rate and the length of the continuous flow reactor. The product flowing out of the continuous flow reactor was diluted, quenched and finally collected at the outlet of the back pressure regulator. Characterizations: Powder X-ray diffraction (XRD) patterns were collected on a Rigaku Ultima IV diffractometer using CuKα radiation (λ=0.15406 nm, 40 kV, 40 mA). The morphology of the products was observed by FE-SEM (JSM-7000F, JEOL) with an accelerating voltage of 15 keV. Nitrogen adsorption-desorption measurements of the calcined samples were performed on an Autosorb-iQ instrument (Quantachrome Instruments) at 77 K. Elemental analysis was performed on a Thermo iCAP 6300 inductively coupled plasma−atomic emission spectrometer (ICP-AES). Solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra were collected by a JEOL ECA 500 spectrometer.

well as the seeds with longer milling periods (Figure S2). Longer milling period resulted in a smaller particle size yet caused a severer amorphization,43-45 which deteriorated the efficiency of the seed. High temperature synthesis with the addition of the 10-min-milled seed was attempted using the tubular reactor. SAPO-CHA product with high yield could be achieved after a synthesis of 30 min under 190 oC (Figure 2A), representing a remarkable enhancement in crystallization rate. However, further increasing the synthesis temperature resulted in the formation of SAPO-AFI as a byproduct (Figure 2B), which indicates that high temperature synthesis reached its limit at 190 oC.

Figure 1. SAPO-CHA seeds. (A) XRD patterns for the reference SAPO-CHA seed and the milled seed obtained by milling the reference seed for 10 min (denoted as 10-min-milled seed). (B) and (C), SEM images for the reference seed and the 10-min-milled seed, respectively.

Results and Discussions A tubular reactor was employed to achieve an environment of rapid heating, and consequently the duration for temperature raise (targeted temperature: 190 oC or 210 oC) could be shortened to about 1 min (Figure S1), which laid a solid foundation for establishing a synthesis route on the order of minutes. The merits of the tubular reactor, however, are beyond avoiding thermal lag that usually exists in the conventional autoclaves. Rather, the rapid temperature raise in the tubular reactor offers us the feasibility to precisely controlling the crystallization kinetics. The particle size of the seed is an important factor that influences the crystallization in a seeded synthesis. Generally, a smaller seed is preferred for a faster crystallization as it can provide a larger external surface where newly formed crystals can growth. In this work, a SAPO-CHA seed obtained by mechanically milling a reference SAPO-CHA sample for 10 min (denoted as 10-min-milled seed hereafter, see SEM image in Figure 1) was used. The 10-minmilled seed showed a higher efficiency in accelerating the crystallization rate than did the reference SAPO-CHA as

To employ a higher temperature and thereof achieve a faster crystallization rate, the pretreatment of Al and Si sources was found to be critical. Instead of adding Al and Si sources separately, we developed a modified procedure to prepare the synthesis precursor, where Al and Si sources were mixed and mechanically milled prior to being mixed with other species to obtain the synthesis precursor. On the basis of this strategy, ultrafast synthesis of SAPO-CHA within 10 min was achieved under 210 oC (Figure 3A). The SEM image in Figure 3B shows that the SAPO-CHA product synthesized for 10 min has a cubic shape with smooth facets, and the TEM image (Figure 3B) demonstrates the well-ordered lattice, both of which indicate that high crystallinity of the fast-synthesized product was obtained. High yield and micropore volume comparable to those of the reference SAPO-CHA seed were achieved after the synthesis for 10 min, as shown in Table 1. In addition, Figure S3 also illustrates the comparable textural properties for the reference SAPO-CHA and the



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fast-synthesized SAPO-CHA. These results convincingly demonstrate that the fast-synthesized SAPO-CHA has the same properties as those of the reference SAPO-CHA, except that the latter has a much larger crystal size.

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Table 1. Yield and micropore volume data for the ultrafast synthesis of SAPO-CHA using the modified procedure. yield(a)

micropore volume(b)

(%)

(cm3/g)

0 min

15.6

0.04

5 min

40.9

0.16

synthesis time

10 min

88.5

0.26

30 min

91.4

0.27

(c)

94.1

0.27

reference seed (a)

Calculated on the basis of the total weight of TO4 in the (b) (c) synthesis precursor. Calculated by the t-plot method. The reference SAPO-CHA seed was synthesized in the conventional autoclave without the addition of any seed.

Figure 2. Synthesis of SAPO-CHA using the original proceo o dure. (A) Synthesis at 190 C. (B) Synthesis at 210 C. (Note that 10 wt% of the 10-min-milled seed was added in both cases).

Si content as well as its distribution in the framework determines the acidity and stability of SAPO-CHA.46-50 In this work, we were able to achieve an ultrafast synthesis of SAPO-CHA with optimum Si content as well as uniform distribution. From solid-state 29Si MAS NMR spectra in Figure 4, a single peak centering at -91.5 ppm was observed for both of the reference SAPO-CHA and the fastsynthesized SAPO-CHA, indicating the presence of only Si(OAl)4 species. Peaks due to Si island (Si(OSi)4 species) and the species with other coordination states (including Si(OSi)(OAl)3, Si(OSi)2(OAl)2 and Si(OSi)3(OAl) species) were not observed. Meanwhile, it is worth noting that the molar ratios of Si in the reference SAPO-CHA and the fast-synthesized SAPO-CHA were characterized as 8.8% and 8.7%, respectively, which are in agreement with the theoretical value of 8.3% for a case where Si(OAl)4 species are uniformly distributed in CHA framework.51,52

29

Figure 3． Ultrafast synthesis of SAPO-CHA using the modified procedure. (A) XRD patterns for the SAPO-CHA products synthesized over different periods. (B) and (C) SEM image and TEM image for the SAPO-CHA product synthesized for 10 min, respectively. (Note that 10 wt% of the 10-minmilled seed was added).

Figure 4. Solid-state Si MAS NMR spectra for the reference SAPO-CHA and the SAPO-CHA product synthesized for 10 min. (Note that the oxygen elements are not shown in the schematic illustration of Si-O-Si and Si-O-Al bonds).

To clarify the role of the pretreatment of Al and Si sources, the evolution of chemical composition in the solid products was examined. As seen from Figure 5, orig-


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inal procedure and modified procedure led to different changes of chemical composition, suggesting two different crystallization pathways exist. In the original procedure, pseudoboehmite was firstly mixed with phosphoric acid aqueous solution, which generated an amorphous aluminophosphate. Silica species existed unreacted and precipitated in the initial stage, contributing to a higher Si content in the solid products (over than 40% as shown in Figure 5A). During the high temperature synthesis (190 o C), reorganization of the aluminophosphate network along with the Si incorporation proceeded, resulting in the gradual formation of crystalline SAPO-CHA. When a higher temperature (210 oC) was employed, however, the aluminophosphate tended to form a primary crystalline phase with AFI structure because of its faster formation rate compared with CHA structure under this condition, which accordingly generated SAPO-AFI as a byproduct. In contrast, in the modified procedure, Al and Si sources were firstly milled and then added to the phosphoric acid aqueous solution. The interaction/reaction between Al and Si sources under milling treatment caused an intrusion to the formation of the aluminophosphate, which can be reflected by the changes in chemical composition. As a consequence, the modified procedure was able to avoid the formation of primary AFI structure, leading to the ultrafast synthesis of SAPO-CHA at a relatively higher temperature.

The appearance of SAPO-AFI in the synthesis using the original procedure at 210 oC indicates that the crystallization of SAPO-AFI should be very fast. As shown in Figure 2B, the formation of SAPO-AFI rapidly proceeded even though the milled SAPO-CHA seed was added. It is thus reasonable to expect that pure phase of SAPO-AFI could be synthesized if no seed or a SAPO-AFI seed was used. With this purpose, the ultrafast synthesis of SAPO-AFI was firstly attempted in a seed-free system. Figure S4 shows that fully crystallized SAPO-AFI was obtained after a synthesis period of 20 min at 210 oC. Using the 20-minsynthesized SAPO-AFI as a seed, the crystallization of SAPO-AFI was much enhanced, resulting in the synthesis of SAPO-AFI in 5 min (Figure 6A). The SEM images (for the SAPO-AFI seed and the fast-synthesized SAPO-AFI, respectively, in Figure 6B and 6C) together with the N2 adsorption-desorption isotherms (Figure S5) confirm the full crystallinity of the fast-synthesized SAPO-AFI.

Figure 6. Ultrafast synthesis of SAPO-AFI in the tubular reactor. (A) XRD patterns for the SAPO-AFI seed and the products synthesized for 0 min, 2 min and 5 min, respectively. (B) and (C) SEM images for the SAPO-AFI seed and the product synthesized for 5 min, respectively.

Figure 5. Evolution of chemical composition in the solid products for the syntheses using different gel preparation procedures. (A) Evolution of chemical composition for the original procedure, where no pretreatment of Al and Si sources were adopted. (B) Evolution of chemical composition for the modified procedure, where milling of Al and Si sources was adopted.

So far, many efforts have been devoted to tune the phase selection between SAPO-CHA and SAPO-AFI, because they are a pair of competing phases due to similarities in compositions and formation conditions.52,53 In this work, we found that phase selection can be achieved by controlling the crystallization kinetics, as SAPO-AFI and SAPO-CHA have clear difference in crystallization rate under specific conditions. Using the tubular reactor, it is very easy to alter the heating rate by changing the heating medium (see Figure S1). Under rapid heating, the targeted temperature can be reached within 1 min, which has proven to be critical to the precise control of crystallization kinetics. As shown in Figure 7A, fast heating at 190 oC and 210 oC could result in the formation of SAPO-CHA and



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SAPO-AFI, respectively; whereas slow heating at 210 oC gave rise to a mixture containing both SAPO-AFI and SAPO-CHA. The crystallinity curves for the synthesis under slow heating (Figure 7B) indicate that SAPO-AFI was firstly formed, and then the formation of SAPO-CHA followed concurrent with a gradual disappearance of SAPOAFI. In this sense, the tubular reactor has proven to be a suitable reactor to realize kinetics control and thus tune the phase selection. In contrast, a mixture of both phases was obtained in the conventional autoclave due to slow temperature raise therein (Figure 7B).

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favoring rapid formation of a primary framework with AFI structure, upon which Si incorporation followed to form SAPO-AFI. This speculation could be supported by the relatively low molar ratio of Si in the SAPO-AFI product (4.4%), probably due to the fact that formation of the parent AFI framework proceeded extremely fast at high temperatures while the Si incorporation lagged behind. Although SAPO-AFI is less stable, as a kinetically preferred phase, it could be recovered as a pure product because the transformation from SAPO-AFI to SAPO-CHA takes much longer time under a condition where almost all the nutrient species have been consumed.

Figure 7. Phase selection between SAPO-CHA and SAPO-AFI. (A) Phase determination using the same precursor by controlling crystallization kinetics (through changing temperature and heating environment) in the tubular reactor. (B) Comparison of operating areas for the tubular reactor and the conventional autoclave in the synthesis of SAPO-AFI (in this case, the original procedure was used to prepare the synthesis precursor, 10 wt% SAPO-AFI seed was added, and the o syntheses were performed at 210 C. “TR” and “Au” denote the tubular reactor and the conventional autoclave, respectively.).

Clearly, judged from kinetics point of view, the crystallization of SAPO-AFI can proceed much faster than that of SAPO-CHA. According to the Ostwald step rule, the crystallization of zeolites follows a route that the first generated phase could convert to a more thermodynamically stable phase and then the next until the most stable phase is formed.54-57 It seems that SAPO-AFI has a higher crystallization rate than SAPO-CHA, because AFI, having a one-dimensional 12-member ring structure, is a less stable phase compared to CHA, which is a three-dimensional structure with smaller pores (Figure 8). Therefore, it is reasonable to speculate that the synthesis at 210 oC using the original procedure may help to create an environment

Figure 8. Illustrations and characteristics of AFI and CHA structures. (A) AFI. (B) CHA.

The ultrashort synthesis period offers a great convenience to develop a continuous flow synthesis. In general, the kinetics, the thermodynamics and the hydrodynamics should be considered comprehensively, and mismatch among these aspects may cause difficulties or even make it impossible to realize a continuous flow synthesis.37 In this study, a precursor with low viscosity was used for the synthesis of silicoaluminophosphates, and the viscosity was maintained at almost the same level throughout the whole crystallization even though the crystals gradually accumulated and precipitated. The low viscosity of the


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Figure 9. Continuous flow synthesis of silicoaluminophosphates. (A) Diagram of the continuous flow synthesis of silicoaluminophosphates. (B) Photograph of the oil bath and the flow reactor immersed therein. (C) Pressure log showing the synchronized fluctuation of the pressures at both ends of the flow reactor. (D) Photograph of the milky slurry flowing out of the flow reactor.

synthesis precursor allowed us to design a one-stage and straightforward continuous flow reactor to synthesize silicoaluminophosphates. Figure 9A shows the flow diagram of the continuous flow synthesis, and Figure 9B depicts the oil bath with the flow reactor immersed. Both SAPO-CHA and SAPO-AFI could be prepared using this apparatus, and the selection of the targeted phase could be easily achieved by changing the synthesis conditions like the precursor preparation procedure, the type of seed and the residence time. A stable flow process was maintained, as indicated by a synchronized fluctuation of the pressures at both inlet and outlet of the flow reactor (Figure 9C). Product flowing out of the continuous flow reactor was a kind of milky slurry (Figure 9D). After separation, the final solid product exhibited the same qualities as those synthesized in the tubular reactor operated in batch. The flow rate of the synthesis mixture was maintained at 0.35 ml/min, which was equivalent to a production rate of 4.5 g SAPOs per hour. Because the actual reactor volumes were quite small (about 1.8 cm3 and 3.6 cm3 for the reactors of SAPO-AFI and SAPO-CHA, respectively), the continuous flow process generated a very high space-time yield. Considering the practical importance of SAPO-CHA and SAPO-AFI, the continuous flow synthesis, with high space-time yield and ease of being scaled up, will surely benefit the mass production of these materials in the future.

Conclusions In this work, we have demonstrated a comprehensive method to achieve the minute-order synthesis of both SAPO-CHA and SAPO-AFI. The fast-synthesized SAPOCHA proved to possess only isolated Si species, indicating great potential in practical applications. The phase determination between SAPO-AFI and SAPO-CHA can be made by controlling the crystallization kinetics using the tubular reactor, and analysis into this phenomenon helped us to reveal the crystallization behaviors of SAPOAFI and SAPO-CHA. Thanks to the minute-order synthesis period, the continuous flow synthesis of silicoaluminophosphates was also established, which is expected to alter the mass production mode of silicoaluminophosphates and other zeolitic catalysts in the future.

ASSOCIATED CONTENT Supporting Information. Heating environments in the tubular reactor, effect of milled seeds on the synthesis of SAPOCHA, synthesis of SAPO-AFI without the addition of seed, N2 adsorption-desorption isotherms for both SAPO-CHA and SAPO-AFI. This material is available free of charge via the Internet at http://pubs.acs.org.



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AUTHOR INFORMATION Corresponding Author

Propene Formation in the MTO Reaction over SAPO-34, Catal.

*[email protected]

Lett. 1993, 20, 329-336.

Author Contributions #

(10) Wilson, S.; Barger, P., The Characteristics of SAPO-34

These authors contributed equally.

Notes

Which Influence the Conversion of Methanol to Light Olefins,

The authors declare on competing financial interest.

Microporous Mesoporous Mater. 1999, 29, 117-126.

ACKNOWLEDGMENT This paper is based on results obtained from the Future Pioneering Program "Research and development of thermal management materials and technology" commissioned by the New Energy and Industrial Technology Development Organization (NEDO), and it has also been supported by the Thermal Management Materials and Technology Research Association (TherMAT). Z.L. is grateful to the Ministry of Education, Culture, Sports, Science and Technology, Japan, for a Japanese Government Scholarship.

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Table of Contents Artwork


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Ultrafast and Continuous Flow Synthesis of Silicoaluminophosphates

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