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Dongyang Xi, Qiming Sun, Xiaoxin Chen, Ning Wang and Jihong Yu* 5
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Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x A facile and green route has been developed for the synthesis of hierarchical zeolite catalysts by recycling waste motherliquors. After three recycles of mother-liquors, the obtained hierarchical SAPO-34 zeolites keep high crystallinity, texture properties, and acidity, as well as excellent MTO catalytic performance as compared to the initially prepared catalysts. Zeolite materials with regular microporous structures have been widely used in many industrial processes such as catalysis, adsorption, and ion-exchange.1-3 These materials are typically prepared under hydrothermal or solvothermal conditions by using alkali ions, amines or quaternary ammonium ions as the structure directing agents (SDAs). Their syntheses generally require excess reactant materials to give rise to a moderate product yield. The desired solid products are separated from the reaction mixtures while the mother-liquors are usually discarded as a waste. However, the filtrated mother-liquors usually contain surplus reactants, in particular organic species (usually toxic and expensive) that can be reused. Presently, green chemistry has received much attention due to increased energy, economy, and environmental concerns.4-6 Great efforts have been made to synthesize zeolites cost-effectively by maximizing the materials efficiency and minimizing the generation of hazardous species.7, 8 For example, Zones et al. reported a facile method by recycling SDAs during zeolite synthesis where the organic amines can be broken into smaller fragments after the synthesis, easily removed from the pores and recombined for reuse.9 Our group also investigated the synthesis of cobalt-substituted aluminophosphate molecular sieves by recycling waste mother-liquors.10 However, the development of efficient green routes to the synthesis of industrially important zeolite catalysts remains a great challenge.11, 12 The silicoaluminophosphate zeolite SAPO-34 (CHA zeotype) with large cavities (9.4 Å in diameter) connected by small 8-ring pore openings (3.8 Å × 3.8 Å) is one of the most excellent
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industrial catalysts for the methanol-to-olefin (MTO) reaction.13Since the MTO process introduces a new way to produce light olefins from the abundant nonpetroleum sources such as nature gas, coal, and biomass, the synthesis of SAPO-34 catalysts with high catalytic performance has gained extensive interest.17-20 Previous studies have shown that when the meso or/and macropores are introduced into the microporous SAPO-34 zeolite crystals, the resulting hierarchical structure can markedly enhance the MTO performance.21-25 In our recent work, we developed a HF-assisted in-situ growth-etching route to synthesize hierarchical SAPO-34 crystals with intracrystalline parallel macrochannels of approximately 100 nm. These hierarchical SAPO-34 catalysts exhibited so far the best MTO catalytic performance under similar catalytic conditions.26 However, excess HF and triethylamine (TEA) used in the synthetic system undoubtedly increase the synthesis cost and environmental pollution. To make use of the excess non-reacted reagents effectively and further enhance the yield of SAPO-34, in this work, we developed a facile and green method by recycling the waste mother-liquors to prepare hierarchical SAPO-34 zeolite catalysts. Importantly, the resulting hierarchical SAPO-34 zeolites show excellent MTO catalytic performance after three recycles of the waste mother-liquors. The initial SAPO-34 zeolite crystals (M0) were prepared in the reaction mixture with molar composition of 0.4 SiO2: 1.0 Al2O3: 1.1 P2O5: 4.7 TEA: 1.9 HF: 70 H2O under hydrothermal conditions at 200 °C for 24 hours.26 After the crystallization, the solid product was separated by centrifugation and the motherliquors were collected and used for the subsequent recycle. At each recycle, we kept the molar ratio of SiO2: Al2O3: P2O5 in the reaction gel unchanged by supplementing inorganic sources (Si, Al, and P) to the mother-liquors without adding extra HF and TEA. 16
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Table 1. Product composition, gel composition, pH of the synthesis systems and the product yield. Samples
Product compositiona
Gel composition
pH
Yield
M0
Si0.10Al0.46P0.44O2
0.40 SiO2: 1.00 Al2O3: 1.10 P2O5: 4.70 TEA: 1.9HF: 70H2O
8.16
34.0%
M1
Si0.11Al0.46P0.43O2
(0.27b+0.13c) SiO2: (0.66b +0.34c) Al2O3: (0.78b +0.32c) P2O5: 4.36 TEAd: ∼1.9HFe: 70H2O
7.70
33.7%
M2
Si0.11Al0.48P0.41O2
(0.25b +0.15c) SiO2: (0.68b +0.32c) Al2O3: (0.81b +0.29c) P2O5: 4.12 TEAd: ∼1.9HFe: 70H2O
7.50
30.0%
M3
Si0.11Al0.48P0.41O2
(0.26b +0.14c) SiO2: (0.67b +0.33c) Al2O3: (0.82b +0.28c) P2O5: 3.91 TEAd: ∼1.9HFe: 70H2O
7.25
30.0%
a
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Measured by inductively coupled plasma (ICP). b The residual inorganic sources in the mother-liquors. c Supplemented inorganic sources to the motherliquors based on those consumed for the product crystallization. d The residual amount of TEA in the mother-liquors based on product TG analysis (Fig. S1, ESI†).e Nearly no change is assumed for HF because only less HF is involved in the products.
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Recyclable Synthesis of Hierarchical Zeolite SAPO-34 with Excellent MTO Catalytic Performance
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Scheme 1. A series of chart illustrating the mother-liquor recyclable synthesis of SAPO-34 (M0, M1, M2, and M3). 30
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repeated 3 times and the products were named as M1, M2, and M3, respectively. The detailed synthesis information and procedure are presented in Table 1 and Scheme 1. At each recycling process, we got the similar product yield of approximately 30% based on the alumina. After three recycles, the utilization ratio of TEA reached up to 22%. The XRD patterns of samples M0, M1, and M2 show typical diffraction peaks of the CHA structure (Fig. 1), while the XRD pattern of the sample M3 reveals that SAPO-5 coexists with SAPO-34 as a minor phase due to the decreased pH value of the reaction gel caused by the consumption of TEA. All of the XRD patterns suggest high crystallinity of the synthesized products. Fig. 2 shows the SEM images of the samples M0-M3. The morphology of samples M1 and M2 obtained by recycling mother-liquors (Fig. 2b, 2c) is almost the same as that of the initial M0 (Fig. 2a). All of these crystals present center-hollowed rhombohedral morphology. The intracrystalline macropores resulting from the dissolution of defect regions as described in our previous work26 is shown in Fig. S2 (ESI†). In the sample M3, a little amount of SAPO-5 zeolite crystals with hexagonal prism morphology is also observed (Fig. 2d).
Fig. 1. XRD patterns of SAPO-34 samples M0, M1, M2, and M3. M3 is co-crystallized with SAPO-5(*).
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Fig. 3. Argon adsorption/desorption isotherms of SAPO-34 samples M0, M1, M2, and M3.
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Fig. 2. SEM images of SAPO-34 samples M0 (a), M1 (b), M2 (c), and M3 (d). 10
For example, when we did the first recycle for the synthesis of SAPO-34 (M1), we added inorganic Si, Al, and P sources the same amount as those included in the solid product M0 (calculated by ICP) to the mother-liquors. These procedures were
This journal is © The Royal Society of Chemistry [year]
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Figure 3 shows the Ar adsorption/desorption isotherms of the resulting SAPO-34 samples. All of the samples exhibit the characteristic Type I adsorption isotherms, while a little uptake near saturation pressure in the isotherms of the resulting materials is observed, which indicates that secondary mesopores or macropores are presented in the crystals.27, 28 All of the assynthesized samples show similar surface areas (~500-540 m2/g) and micropore volumes (0.20-0.23 cm3/g). Solid-state 29Si MAS NMR spectra of the calcined samples of M0 to M3 are shown in Fig. S3 (ESI†). The samples synthesized by recycling mother-liquors exhibit similar chemical shifts compared to the initial SAPO-34 crystals, which indicates that all of the samples possess the similar coordination states of Si atoms.29 Fig. S4 (ESI†) shows the NH3-TPD profiles of all samples. Samples M1 and M2 synthesized by recycling motherliquors have almost the same acidic strength and concentration in strong acid sites compared to the sample M0, while the sample M3 possesses slightly higher acidity due to the existence of a little amount of SAPO-5 crystals. [journal], [year], [vol], 00–00 | 2
ChemComm Accepted Manuscript
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DOI: 10.1039/C5CC03904E
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Fig. 4. Methanol conversion variation and selectivities with time-onstream over M0 to M3 catalysts. Experimental conditions: WHSV = 2 h-1, T = 673 K, catalyst weight = 300 mg.
In summary, hierarchical silicoaluminophosphate SAPO-34 zeolites have been successfully synthesized by a facile and green route via recycling waste mother-liquors. The synthesized catalysts show high MTO catalytic performance after three recycles of mother-liquors, which is comparable to the initially prepared catalyst. The recycling mother-liquor route can effectively decrease the wastes of raw materials and environmental pollution, proving to be cost-effective and environment-friendly for the synthesis of industrially important zeolite catalysts. We thank the State Basic Research Project of China (Grant No. 2011CB808703) and National Natural Science Foundation of China (Grant Nos: 91122029, 21401067 and 21320102001) for supporting this work.
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China [email protected] † Electronic Supplementary Information (ESI) available: More details of experimental and characterization processes, 29Si MAS NMR and NH3TPD, and the MTO catalytic results. See DOI: 10.1039/b000000x/
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J. Čejka, H. van Bekkum, A. Corma and F. Schüth, Introduction to zeolite science and practice, in studies in surface science and catalysis 168, Elsevier BV Amsterdam, Neth, 2007. 2. A. Corma, Chem. Rev., 1997, 97, 2373-2420. 3. Z. Wang, J. Yu and R. Xu, Chem. Soc. Rev., 2012, 41, 1729-1741. 4. H. Lee, S. I. Zones and M. E. Davis, Nature, 2003, 425, 385-388. 5. R. Rinaldi and F. Schüth, Energy Environ. Sci., 2009, 2, 610-626. 6. X. Meng and F. S. Xiao, Chem Rev, 2014, 114, 1521-1543. 7. Q. Qian, J. Ruiz-Martínez, M. Mokhtar, A. M. Asiri, S. A. AlThabaiti, S. N. Basahel and B. M. Weckhuysen, ChemCatChem, 2014, 6, 772-783. 8. H. Pan, Q. Pan, Y. Zhao, Y. Luo, X. Shu and M. He, Ind. Eng. Chem. Res., 2010, 49, 7294-7302. 9. S. Zones, H. Lee, M. Davis, J. Casci and A. Burton, Stud. Surf. Sci. Catal., 2005, 158, 1-10. 10. F. Duan, J. Li, P. Chen, J. Yu and R. Xu, Microporous Mesoporous Mater., 2009, 126, 26-31. 11. E.-P. Ng, L. Delmotte and S. Mintova, Green Chemistry, 2008, 10, 1043-1048. 12. D. Fan, P. Tian, S. Xu, Q. Xia, X. Su, L. Zhang, Y. Zhang, Y. He and Z. Liu, J. Mater. Chem., 2012, 22, 6568-6574. 13. S. T. Wilson, B. M. Lok, C. A. Messina, T. R. Cannan and E. M. Flanigen, J. Am. Chem. Soc., 1982, 104, 1146-1147. 14. Y. Li and J. Yu, Chem. Rev., 2014, 114, 7268-7316. 15. U. Olsbye, S. Svelle, M. Bjorgen, P. Beato, T. V. Janssens, F. Joensen, S. Bordiga and K. P. Lillerud, Angew. Chem. Int. Ed., 2012, 51, 58105831. 16. C. Baerlocher and L. McCusker, can be found under http://www. izastructure. org/databases, 2012. 17. Y. Jin, Q. Sun, G. Qi, C. Yang, J. Xu, F. Chen, X. Meng, F. Deng and F. S. Xiao, Angew. Chem. Int. Ed., 2013, 52, 9172-9175. 18. S. M. A. Ahmadi, S. Askari and R. Halladj, Afinidad, 2013, 70, 130138. 19. Q. Sun, Y. Ma, N. Wang, X. Li, D. Xi, J. Xu, F. Deng, K. B. Yoon, P. Oleynikov , O. Terasaki and J. Yu, J. Mater. Chem. A, 2014, 2, 1782817839. 20. Z. Li, J. Martinez-Triguero, P. Concepcion, J. Yu and A. Corma, PCCP, 2013, 15, 14670-14680. 21. H. Yang, Z. Liu, H. Gao and Z. Xie, J. Mater. Chem., 2010, 20, 32273231. 22. Q. Sun, N. Wang, D. Xi, M. Yang and J. Yu, Chem. Commun., 2014, 50, 6502-6505. 23. J. Zhu, Y. Cui, Y. Wang and F. Wei, Chem. Commun., 2009, 32823284. 24. M. Yang, P. Tian, C. Wang, Y. Yuan, Y. Yang, S. Xu, Y. He and Z. Liu, Chem. Commun., 2014, 50, 1845-1847. 25. G. Yang, Y. Wei, S. Xu, J. Chen, J. Li, Z. Liu, J. Yu and R. Xu, J. Phys. Chem. C, 2013, 117, 8214-8222. 26. D. Xi, Q. Sun, J. Xu, M. Cho, H. S. Cho, S. Asahina, Y. Li, F. Deng, O. Terasaki and J. Yu, J. Mater. Chem. A, 2014, 2, 17994-18004. 27. V. Valtchev, E. Balanzat, V. Mavrodinova, I. Diaz, J. El Fallah and J. M. Goupil, J. Am. Chem. Soc., 2011, 133, 18950-18956. 28. X. Chen, T. Todorova, A. Vimont, V. Ruaux, Z. Qin, J. P. Gilson and V. Valtchev, Microporous Mesoporous Mater., 2014, 200, 334-342. 29. P. Tian, Y. Wei, M. Ye and Z. Liu, ACS Catalysis, 2015, 5, 1922-1938.
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Catalytic tests of methanol conversion were performed in a fixed bed reactor at 673 K over the resulting hierarchical SAPO34 catalysts. Fig. 4, Fig. S5 (ESI†) and Table S1 (ESI†) show the conversions versus time-on-stream (TOS) and selectivities of products over the catalysts. The catalytic lifetimes of hierarchical SAPO-34 M0 to M3 are 506, 446, 466, and 486 min, respectively. Due to the enhanced mass transfer within the macrochannels and reduced coke deposition, the lifetimes of the hierarchical SAPO34 catalysts synthesized by recycling mother-liquors are much higher than that of 226 min for the conventional SAPO-34 synthesized without adding HF.26 Although the sample M3 synthesized by the third recycle contains a little amount of SAPO-5, the lifetime can also reach up to 486 min, indicating that after three recycles, the catalysts still have excellent MTO activity. The selectivities of ethylene and propylene versus TOS over the hierarchical SAPO-34 catalysts M0 to M3 are 84.8%, 83.6%, 84.7%, and 83.7%, respectively, which are evidently higher than that of the conventional SAPO-34 without adding HF (77.0%).24 According to the catalytic test, it can be seen that the catalysts synthesized after three recycles of mother-liquors can still keep high MTO performance, proving the successfulness of the recycling mother-liquors route to synthesize the hierarchical SAPO-34 catalysts with high performance.
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ChemComm Accepted Manuscript
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Hierarchical zeolite SAPO-34 is obtained via a facile and green route by recycling waste mother-liquors, which shows high MTO catalytic activity and selectivity.
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 4
ChemComm Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: D. Xi, Q. Sun, X. Chen, N. Wang and J. Yu, Chem. Commun., 2015, DOI: 10.1039/C5CC03904E.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
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Dongyang Xi, Qiming Sun, Xiaoxin Chen, Ning Wang and Jihong Yu* 5
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Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x A facile and green route has been developed for the synthesis of hierarchical zeolite catalysts by recycling waste motherliquors. After three recycles of mother-liquors, the obtained hierarchical SAPO-34 zeolites keep high crystallinity, texture properties, and acidity, as well as excellent MTO catalytic performance as compared to the initially prepared catalysts. Zeolite materials with regular microporous structures have been widely used in many industrial processes such as catalysis, adsorption, and ion-exchange.1-3 These materials are typically prepared under hydrothermal or solvothermal conditions by using alkali ions, amines or quaternary ammonium ions as the structure directing agents (SDAs). Their syntheses generally require excess reactant materials to give rise to a moderate product yield. The desired solid products are separated from the reaction mixtures while the mother-liquors are usually discarded as a waste. However, the filtrated mother-liquors usually contain surplus reactants, in particular organic species (usually toxic and expensive) that can be reused. Presently, green chemistry has received much attention due to increased energy, economy, and environmental concerns.4-6 Great efforts have been made to synthesize zeolites cost-effectively by maximizing the materials efficiency and minimizing the generation of hazardous species.7, 8 For example, Zones et al. reported a facile method by recycling SDAs during zeolite synthesis where the organic amines can be broken into smaller fragments after the synthesis, easily removed from the pores and recombined for reuse.9 Our group also investigated the synthesis of cobalt-substituted aluminophosphate molecular sieves by recycling waste mother-liquors.10 However, the development of efficient green routes to the synthesis of industrially important zeolite catalysts remains a great challenge.11, 12 The silicoaluminophosphate zeolite SAPO-34 (CHA zeotype) with large cavities (9.4 Å in diameter) connected by small 8-ring pore openings (3.8 Å × 3.8 Å) is one of the most excellent
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industrial catalysts for the methanol-to-olefin (MTO) reaction.13Since the MTO process introduces a new way to produce light olefins from the abundant nonpetroleum sources such as nature gas, coal, and biomass, the synthesis of SAPO-34 catalysts with high catalytic performance has gained extensive interest.17-20 Previous studies have shown that when the meso or/and macropores are introduced into the microporous SAPO-34 zeolite crystals, the resulting hierarchical structure can markedly enhance the MTO performance.21-25 In our recent work, we developed a HF-assisted in-situ growth-etching route to synthesize hierarchical SAPO-34 crystals with intracrystalline parallel macrochannels of approximately 100 nm. These hierarchical SAPO-34 catalysts exhibited so far the best MTO catalytic performance under similar catalytic conditions.26 However, excess HF and triethylamine (TEA) used in the synthetic system undoubtedly increase the synthesis cost and environmental pollution. To make use of the excess non-reacted reagents effectively and further enhance the yield of SAPO-34, in this work, we developed a facile and green method by recycling the waste mother-liquors to prepare hierarchical SAPO-34 zeolite catalysts. Importantly, the resulting hierarchical SAPO-34 zeolites show excellent MTO catalytic performance after three recycles of the waste mother-liquors. The initial SAPO-34 zeolite crystals (M0) were prepared in the reaction mixture with molar composition of 0.4 SiO2: 1.0 Al2O3: 1.1 P2O5: 4.7 TEA: 1.9 HF: 70 H2O under hydrothermal conditions at 200 °C for 24 hours.26 After the crystallization, the solid product was separated by centrifugation and the motherliquors were collected and used for the subsequent recycle. At each recycle, we kept the molar ratio of SiO2: Al2O3: P2O5 in the reaction gel unchanged by supplementing inorganic sources (Si, Al, and P) to the mother-liquors without adding extra HF and TEA. 16
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Table 1. Product composition, gel composition, pH of the synthesis systems and the product yield. Samples
Product compositiona
Gel composition
pH
Yield
M0
Si0.10Al0.46P0.44O2
0.40 SiO2: 1.00 Al2O3: 1.10 P2O5: 4.70 TEA: 1.9HF: 70H2O
8.16
34.0%
M1
Si0.11Al0.46P0.43O2
(0.27b+0.13c) SiO2: (0.66b +0.34c) Al2O3: (0.78b +0.32c) P2O5: 4.36 TEAd: ∼1.9HFe: 70H2O
7.70
33.7%
M2
Si0.11Al0.48P0.41O2
(0.25b +0.15c) SiO2: (0.68b +0.32c) Al2O3: (0.81b +0.29c) P2O5: 4.12 TEAd: ∼1.9HFe: 70H2O
7.50
30.0%
M3
Si0.11Al0.48P0.41O2
(0.26b +0.14c) SiO2: (0.67b +0.33c) Al2O3: (0.82b +0.28c) P2O5: 3.91 TEAd: ∼1.9HFe: 70H2O
7.25
30.0%
a
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Measured by inductively coupled plasma (ICP). b The residual inorganic sources in the mother-liquors. c Supplemented inorganic sources to the motherliquors based on those consumed for the product crystallization. d The residual amount of TEA in the mother-liquors based on product TG analysis (Fig. S1, ESI†).e Nearly no change is assumed for HF because only less HF is involved in the products.
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[journal], [year], [vol], 00–00 | 1
ChemComm Accepted Manuscript
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Recyclable Synthesis of Hierarchical Zeolite SAPO-34 with Excellent MTO Catalytic Performance
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Scheme 1. A series of chart illustrating the mother-liquor recyclable synthesis of SAPO-34 (M0, M1, M2, and M3). 30
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repeated 3 times and the products were named as M1, M2, and M3, respectively. The detailed synthesis information and procedure are presented in Table 1 and Scheme 1. At each recycling process, we got the similar product yield of approximately 30% based on the alumina. After three recycles, the utilization ratio of TEA reached up to 22%. The XRD patterns of samples M0, M1, and M2 show typical diffraction peaks of the CHA structure (Fig. 1), while the XRD pattern of the sample M3 reveals that SAPO-5 coexists with SAPO-34 as a minor phase due to the decreased pH value of the reaction gel caused by the consumption of TEA. All of the XRD patterns suggest high crystallinity of the synthesized products. Fig. 2 shows the SEM images of the samples M0-M3. The morphology of samples M1 and M2 obtained by recycling mother-liquors (Fig. 2b, 2c) is almost the same as that of the initial M0 (Fig. 2a). All of these crystals present center-hollowed rhombohedral morphology. The intracrystalline macropores resulting from the dissolution of defect regions as described in our previous work26 is shown in Fig. S2 (ESI†). In the sample M3, a little amount of SAPO-5 zeolite crystals with hexagonal prism morphology is also observed (Fig. 2d).
Fig. 1. XRD patterns of SAPO-34 samples M0, M1, M2, and M3. M3 is co-crystallized with SAPO-5(*).
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Fig. 3. Argon adsorption/desorption isotherms of SAPO-34 samples M0, M1, M2, and M3.
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Fig. 2. SEM images of SAPO-34 samples M0 (a), M1 (b), M2 (c), and M3 (d). 10
For example, when we did the first recycle for the synthesis of SAPO-34 (M1), we added inorganic Si, Al, and P sources the same amount as those included in the solid product M0 (calculated by ICP) to the mother-liquors. These procedures were
This journal is © The Royal Society of Chemistry [year]
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Figure 3 shows the Ar adsorption/desorption isotherms of the resulting SAPO-34 samples. All of the samples exhibit the characteristic Type I adsorption isotherms, while a little uptake near saturation pressure in the isotherms of the resulting materials is observed, which indicates that secondary mesopores or macropores are presented in the crystals.27, 28 All of the assynthesized samples show similar surface areas (~500-540 m2/g) and micropore volumes (0.20-0.23 cm3/g). Solid-state 29Si MAS NMR spectra of the calcined samples of M0 to M3 are shown in Fig. S3 (ESI†). The samples synthesized by recycling mother-liquors exhibit similar chemical shifts compared to the initial SAPO-34 crystals, which indicates that all of the samples possess the similar coordination states of Si atoms.29 Fig. S4 (ESI†) shows the NH3-TPD profiles of all samples. Samples M1 and M2 synthesized by recycling motherliquors have almost the same acidic strength and concentration in strong acid sites compared to the sample M0, while the sample M3 possesses slightly higher acidity due to the existence of a little amount of SAPO-5 crystals. [journal], [year], [vol], 00–00 | 2
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Fig. 4. Methanol conversion variation and selectivities with time-onstream over M0 to M3 catalysts. Experimental conditions: WHSV = 2 h-1, T = 673 K, catalyst weight = 300 mg.
In summary, hierarchical silicoaluminophosphate SAPO-34 zeolites have been successfully synthesized by a facile and green route via recycling waste mother-liquors. The synthesized catalysts show high MTO catalytic performance after three recycles of mother-liquors, which is comparable to the initially prepared catalyst. The recycling mother-liquor route can effectively decrease the wastes of raw materials and environmental pollution, proving to be cost-effective and environment-friendly for the synthesis of industrially important zeolite catalysts. We thank the State Basic Research Project of China (Grant No. 2011CB808703) and National Natural Science Foundation of China (Grant Nos: 91122029, 21401067 and 21320102001) for supporting this work.
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China [email protected] † Electronic Supplementary Information (ESI) available: More details of experimental and characterization processes, 29Si MAS NMR and NH3TPD, and the MTO catalytic results. See DOI: 10.1039/b000000x/
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Catalytic tests of methanol conversion were performed in a fixed bed reactor at 673 K over the resulting hierarchical SAPO34 catalysts. Fig. 4, Fig. S5 (ESI†) and Table S1 (ESI†) show the conversions versus time-on-stream (TOS) and selectivities of products over the catalysts. The catalytic lifetimes of hierarchical SAPO-34 M0 to M3 are 506, 446, 466, and 486 min, respectively. Due to the enhanced mass transfer within the macrochannels and reduced coke deposition, the lifetimes of the hierarchical SAPO34 catalysts synthesized by recycling mother-liquors are much higher than that of 226 min for the conventional SAPO-34 synthesized without adding HF.26 Although the sample M3 synthesized by the third recycle contains a little amount of SAPO-5, the lifetime can also reach up to 486 min, indicating that after three recycles, the catalysts still have excellent MTO activity. The selectivities of ethylene and propylene versus TOS over the hierarchical SAPO-34 catalysts M0 to M3 are 84.8%, 83.6%, 84.7%, and 83.7%, respectively, which are evidently higher than that of the conventional SAPO-34 without adding HF (77.0%).24 According to the catalytic test, it can be seen that the catalysts synthesized after three recycles of mother-liquors can still keep high MTO performance, proving the successfulness of the recycling mother-liquors route to synthesize the hierarchical SAPO-34 catalysts with high performance.
ChemComm
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DOI: 10.1039/C5CC03904E
Table of Contents (ToC) graphic:
ChemComm Accepted Manuscript
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Hierarchical zeolite SAPO-34 is obtained via a facile and green route by recycling waste mother-liquors, which shows high MTO catalytic activity and selectivity.
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[journal], [year], [vol], 00–00 | 4
