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| Hierarchical SAPO-34 templated by amphiphilic single-quaternary-ammonium surfactants |
| Author Name | Affiliation | E-mail | | SHEN Xue-Feng | SINOPEC Shanghai Research Institute of Petrochemical Technology Co., Ltd, Shanghai 201208, China
State Key Laboratory of Green Chemical Engineering and Industrial Catalysis, Shanghai 201208, China | | | DING Jia-Jia | SINOPEC Shanghai Research Institute of Petrochemical Technology Co., Ltd, Shanghai 201208, China
State Key Laboratory of Green Chemical Engineering and Industrial Catalysis, Shanghai 201208, China | | | LIU Hong-Xing | SINOPEC Shanghai Research Institute of Petrochemical Technology Co., Ltd, Shanghai 201208, China
State Key Laboratory of Green Chemical Engineering and Industrial Catalysis, Shanghai 201208, China | liuhx.sshy@sinopec.com |
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| Abstract: The introduction of mesopores and downsizing of the crystals of SAPO-34 can enhance its diffusion efficiency, leading to high catalytic activity in methanol-to-olefin (MTO) reactions. Amphiphilic single-quaternary-ammonium molecules with different lengths of carbon chains ([N+(CH2CH3)3-CnH2n+1] [Br-], Cn-1N (n=4, 6, 8)) were designed and synthesized as co-structure directing agents. Due to the electrostatic interaction, amphiphilic molecules acted as crystal growth inhibitors or pore-forming agents, which resulted in the formation of hierarchical SAPO-34 (HS) zeolite with a smaller crystal size. When the carbon chain length was four (C4-1N), the hierarchical SAPO-34 zeolite (HS-4) was synthesized with a smaller crystal size and without other crystal phases. SAPO-34 zeolites with high mesopore volume (HS-6 and HS-8) were synthesized with C6-1N and C8-1N as co-structure directing agents. Without adding a co-structure directing agent, conventional SAPO-34 (CS) was synthesized. There were many tetrahedral particles in CS, which is the early morphology of the cubic particles. The results of the X-ray fluorescence spectrometer (XRF) and 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) indicated that Cn-1N molecules restrain Si atoms from incorporating into the AlPO4 framework. The results of NH3-temperature-programmed desorption (NH3-TPD) proved the strong acid gradually decreases in the order of CS > HS-8 > HS-6 > HS-4. The diffusion behaviors of methanol molecules in HS-4, HS-6, and HS-8 were better than in CS. HS-4 showed excellent catalytic performance in MTO reaction:the selectivity of ethylene (C2H4) and propylene (C3H6) (84.4%) has improved by about 4% compared to that of CS (80.5%), and the catalyst lifetime of HS-4 was about two times the lifetime of CS. HS-6 also exhibited high selectivity of C2H4 and C3H6 (83.5%), and its lifetime was almost the same as HS-4. HS-8 had a high mesopore volume, but the higher strong acidity promoted hydrogen transfer reactions, leading to alkanes, aromatics, and coke, so the lifetime of HS-8 in MTO reaction was slightly prolonged. |
| Keywords: SAPO-34 amphiphilic molecules hierarchical pores methanol-to-olefin reaction |
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| SHEN Xue-Feng,DING Jia-Jia,LIU Hong-Xing.Hierarchical SAPO-34 templated by amphiphilic single-quaternary-ammonium surfactants[J].Chinese Journal of Inorganic Chemistry,2023,39(11):2065-2073. |
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